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Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis
The Journal of Physiology
Abstract
Key points
A single bolus of ∼20 g of protein after a bout of resistance exercise provides a maximal anabolic stimulus during the early post‐exercise recovery period (∼5 h), but the effect of various protein feeding strategies on skeletal muscle protein synthesis during an extended recovery period (12 h) is unknown.
We compared three different patterns of ingestion of 80 g of protein during 12 h recovery after resistance exercise and the associated anabolic response in human skeletal muscle. Protein was ingested in 10, 20 or 40 g feedings using a pulsed, intermediate or bolus ingestion regimen, respectively.
Our results indicate that repeated ingestion of 20 g of protein was superior for stimulating muscle protein synthesis during the 12 h experimental period.
The three dietary treatments induced differential phosphorylation of signalling proteins and changes in mRNA abundance.
This study shows that the distribution of protein intake is an important variable to promote attainment and maintenance of peak muscle mass.
Abstract Quantity and timing of protein ingestion are major factors regulating myofibrillar protein synthesis (MPS). However, the effect of specific ingestion patterns on MPS throughout a 12 h period is unknown. We determined how different distributions of protein feeding during 12 h recovery after resistance exercise affects anabolic responses in skeletal muscle. Twenty‐four healthy trained males were assigned to three groups ( n = 8/group) and undertook a bout of resistance exercise followed by ingestion of 80 g of whey protein throughout 12 h recovery in one of the following protocols: 8 × 10 g every 1.5 h (PULSE); 4 × 20 g every 3 h (intermediate: INT); or 2 × 40 g every 6 h (BOLUS). Muscle biopsies were obtained at rest and after 1, 4, 6, 7 and 12 h post exercise. Resting and post‐exercise MPS ( l ‐[ ring ‐ ¹³ C 6 ] phenylalanine), and muscle mRNA abundance and cell signalling were assessed. All ingestion protocols increased MPS above rest throughout 1–12 h recovery (88–148%, P < 0.02), but INT elicited greater MPS than PULSE and BOLUS (31–48%, P < 0.02). In general signalling showed a BOLUS>INT>PULSE hierarchy in magnitude of phosphorylation. MuRF‐1 and SLC38A2 mRNA were differentially expressed with BOLUS. In conclusion, 20 g of whey protein consumed every 3 h was superior to either PULSE or BOLUS feeding patterns for stimulating MPS throughout the day. This study provides novel information on the effect of modulating the distribution of protein intake on anabolic responses in skeletal muscle and has the potential to maximize outcomes of resistance training for attaining peak muscle mass.
... Nevertheless, a recent systematic review analyzing 147 studies found that dietary inadequacies are present in both plant-based diet followers (vegans and vegetarians) and meat-eaters [82]. According to the study, individuals following plant-based diets showed a lower intake and status of vitamin B12 and D, as well as EPA, DHA, calcium, zinc, iodine, and iron (especially in women) compared to meat-eaters, thereby increasing their risk of deficiency. ...
... However, despite higher intakes among meat-eaters, they were still at risk of deficiency in certain nutrients. Interestingly, vegans and vegetarians consumed higher amounts of other nutrients such as PUFA, ALA, fiber, folate, magnesium, vitamin E, B1, B6, and vitamin C [82]. ...
... Dietary plant protein has been linked to reduced cardiovascular risk factors, such as lower blood pressure, improved lipid profiles, and better glucose control [15]. Conversely, although epidemiological studies have focused on the potential adverse effects of animal protein on risks such as elevated blood pressure and central obesity [83,84], individuals following plant-based diets may still be at risk of nutrient deficiencies [82]. ...
The environmental impact of unhealthy diets and the obese population is becoming clearer. However, little is known about the impact of 'healthy' diets related to 'fitness' lifestyles, such as diets directed to gain muscle mass and lose body fat, or the diets of the physically active population. This paper aims to evaluate the Dietary Water Footprint (DWF) of a representative sample of the Guadalajara Metropolitan Area, Mexico, identifying differences according to body composition (levels of fat and muscle) and physical activity (type and intensity), with a focus on contrasting active, healthy lifestyles (i.e., fitness) with sedentary and obesogenic patterns and examining protein consumption. A validated and adapted Food Frequency Questionnaire (FFQ) was applied to 400 adults (18-74 years) from the Guadalajara Metropolitan Area. The participants were grouped according to their body fat and muscle mass levels and physical activity type and intensity. DWF, food and nutrient intake, and adequacy were calculated. The DWF of the sample with a low body fat, a high muscle mass, moderate to intense exercise, and anaerobic exercise (i.e., 'fitness' lifestyle) was up to 800 L per person per day (L/p/d) higher than the sedentary/obese populations. Risks of a high DWF were found as protein intake increases (OR = 6; p < 0.0001). Although unhealthy diets linked to obesity are a major environmental problem, 'fitness' lifestyles can have serious environmental implications.
... g/kg/day, an amount considered sufficient for increasing and maintaining muscle mass through a positive protein balance (Jäger et al., 2017). To guarantee the pool of blood amino acids and optimize the effects of protein in the sports context, protein intake should be distributed between 4 and 5 meals/day (Areta et al., 2013). The response of muscle protein synthesis, during a period of 12 h after exercise, seems to be maximized when four doses of 20 g of high biological value protein are ingested every 3 h after exercise (Areta et al., 2013;Churchward-Venne et al., 2013;Jäger et al., 2017). ...
... To guarantee the pool of blood amino acids and optimize the effects of protein in the sports context, protein intake should be distributed between 4 and 5 meals/day (Areta et al., 2013). The response of muscle protein synthesis, during a period of 12 h after exercise, seems to be maximized when four doses of 20 g of high biological value protein are ingested every 3 h after exercise (Areta et al., 2013;Churchward-Venne et al., 2013;Jäger et al., 2017). Another more precise way of expressing this recommendation is to make it relative to the athlete's body mass, that is, from 0.25 to 0.3 g/kg of the athlete's weight Shaw et al., 2014). ...
... Protein intake was expressed in grams (g) and relative to body mass (g/kg) or meal (g/meal). Protein intake was compared to current sports nutrition recommendations as follows: total daily protein intake (1.4-2.0 g/kg/ d) (Jäger et al., 2017); distribution of protein intake in each meal throughout the day (20-25 g/meal) (Areta et al., 2013;Jäger et al., 2017); post-exercise (i.e. after swimming sessions) protein intake (≤ 3 h post-training; 0.25-0.30 g/kg) Shaw et al., 2014); and pre-sleep protein intake (up to 2 h before sleep; 30-40 g) (Holwerda et al., 2016;Trommelen and Loon, 2016). ...
Background: Proteins are essential for the maintenance, repair, and growth of muscle mass. This is particularly important for master athletes because aging has been associated with loss of muscle mass, function, and strength. Moreover, the timing of intake has been shown important for the best protein utilization. Aim: To analyze timing, quantity, and source of dietary protein in competitive master athletes according to current recommendations. Methods: Twenty-one male master swimmers (47.9 ± 10.0 years; 79.2 ± 6.5 kg; 179.1 ± 5.5 cm; 23.5 ± 4.9% body fat; 73.3 ± 4.2% lean mass) participated in this cross-sectional study. Protein intake was analyzed based on 7-day food records, regarding quantity, timing, and sources of intake. Protein intake was evaluated according to current international sports nutrition guidelines, including the International Society of Sports Nutrition Position Stand. Body fat (%) and lean mass (%) were evaluated using dual-energy X-ray absorptiometry. Results: Participants' mean protein intakes were 1.9 ± 0.5 g/kg/day, 0.6 ± 0.2 g/kg/ meal post-training, and 33.5 ± 23.9 g during the pre-sleep period. Daily intake was within the recommended values of 1.4 and 2.0 g/kg/day (p = 0.01 and 0.147, respectively). Mean pre-sleep intake was within the recommendation values of 30-40 g (p = 0.28 and 0.147, respectively). Most of the daily protein intake was consumed at lunch (66.7 ± 6.9 g) and dinner (48.0 ± 4.5 g). Regarding protein sources, intakes from animal, vegetal, and supplements were, respectively, 65.7%, 29.2%, and 5.1%. Conclusion: Master swimmers presented a total protein intake within the recommendations for a daily basis, but the majority of intake was at lunch and dinner. Protein intake could be better distributed throughout the day to optimize protein synthesis. Guidance on daily protein intake distribution should be reinforced in clinical practice.
... Specifically, to consider what these findings mean: (a) for the importance of daily protein distribution for muscle anabolism and metabolic health, and (b) for the upper limit (or lack thereof) in resistance-trained young women. Trommelen et al. (2023) challenge the generally accepted viewpoint that protein meal distribution represents an important nutritional variable in modulating the anabolic response to ingested protein when combined with resistance exercise (Areta et al., 2013;Loenneke et al., 2016;Moore et al., 2012). This assertion stems from the dosedependent (100PRO > 25PRO) increase in magnitude and duration of hyperaminoacidemia, and the subsequent MPS response to ingested protein following exercise that was observed in the absence of a notable increase in amino acid oxidation rates. ...
... Over a decade ago, the study design of Areta et al. (2013) distributed 80 g of protein as either 8× 10 g boluses spaced 1.5 hr apart (PULSE), 4× 20 g boluses spaced 3 hr apart (INTERMEDIATE), or 2× 40 g boluses spaced 6 hr apart (BOLUS) in resistance-trained young men. Aligned with Trommelen et al. (2023), the temporal response of MPS was measured over a 12-hr postprandial period, albeit following an acute bout of leg-only, rather than whole-body resistance exercise. ...
... Aligned with Trommelen et al. (2023), the temporal response of MPS was measured over a 12-hr postprandial period, albeit following an acute bout of leg-only, rather than whole-body resistance exercise. Areta et al. (2013) reported a greater cumulative 12-hr MPS response in INTERMEDIATE than BOLUS or PULSE that was primarily driven during the intermediate (4-6 hr) and later (6-12 hr) postprandial phases, rather than the early (1-4 hr) postprandial period. Unfortunately, this study did not include a 1× 80 g bolus arm; hence, a similar feast-like comparison to Trommelen et al. (2023) was not possible. ...
A comprehensive recent study by Trommelen et al. demonstrated that muscle tissue exhibits a greater capacity to incorporate exogenous exogenous protein-derived amino acids into bound muscle protein than was previously appreciated, at least when measured in “anabolically sensitive,” recreationally active (but not resistance-trained), young men following resistance exercise. Moreover, this study demonstrated that the duration of the postprandial period is modulated by the dose of ingested protein contained within a meal, that is, the postexercise muscle protein synthesis response to protein ingestion was more prolonged in 100PRO than 25PRO. Both observations represent important scientific advances in the field of protein metabolism. However, we respectfully caution that the practical implications of these findings may have been misinterpreted, at least in terms of dismissing the concept of protein meal distribution as an important factor in optimizing muscle tissue anabolism and/or metabolic health. Moreover, based on emerging evidence, this idea that the anabolic response to protein ingestion has no upper limit does not appear to translate to resistance-trained young women.
... Some evidence suggests that evenly distributing protein intake across meals helps sustain MPS and overall protein utilisation. [75] For example, during breakfast, incorporating protein sources such as eggs, yogurt, or dairy products can provide a solid foundation of protein intake, and during lunch and dinner, including around 200 g of lean meat or fish. These animal protein sources are rich in essential amino acids, crucial for muscle repair and growth. ...
... Some evidence suggests that evenly distributing protein intake across meals helps sustain MPS and overall protein utilization. [75] For example, during breakfast, incorporating protein sources such as eggs, yogurt, or dairy products can provide a solid foundation of protein intake, and during lunch and dinner, including around 200 g of lean meat or fish. These animal protein sources are rich in essential amino acids, crucial for muscle repair and growth. ...
Sarcopenia typically presents in people older than 65 years with signs and symptoms of low muscle strength and low physical performance, such as falls, feeling weak, walking slowly, difficulty rising from a chair, and loss of weight and muscle mass.
The five-item SARC-F patient questionnaire and assessing gait speed are recommended for screening people for suspected sarcopenia. A SARC-F score ≥4 and/or a low usual gait speed indicate low muscle function. Use hand grip or the sit-stand test to assess muscle strength.
Use imaging, such as computed tomography (CT), magnetic resonance imaging (MRI), or dual x-ray absorptiometry (DXA) to assess muscle quality/quantity. Bioimpedance analysis is another diagnostic option, but is less accurate.
In people with confirmed sarcopenia, initiate an exercise or rehabilitation program that focuses on resistance training and balance exercises, combined with dietary intervention to increase protein intake and improve overall calorie intake and quality.
... Furthermore, many studies have shown timing of caloric intake pre-vs. post-exercise to have heterogenous effects on muscle protein breakdown and synthesis, which could, in turn, also influence glucose homeostasis [34,[66][67][68]. For instance, consuming a balanced meal following exercise may mitigate muscle protein breakdown early in the day [68], whereas others have found that ingesting protein every three hours was the best way to stimulate muscle protein synthesis [13,67]. ...
... post-exercise to have heterogenous effects on muscle protein breakdown and synthesis, which could, in turn, also influence glucose homeostasis [34,[66][67][68]. For instance, consuming a balanced meal following exercise may mitigate muscle protein breakdown early in the day [68], whereas others have found that ingesting protein every three hours was the best way to stimulate muscle protein synthesis [13,67]. Despite strides in nutrition research, little work has been conducted related to exercise-diet combined interventions; thus, more combined intervention studies, as in this pilot intervention, should be conducted. ...
Background: The role of protein in glucose homeostasis has demonstrated conflicting results. However, little research exists on its impact following weight loss. This study examined the impact of protein supplementation on glucose homeostasis in older adults >65 years with obesity seeking to lose weight. Methods: A 12-week, nonrandomized, parallel group intervention of protein (PG) and nonprotein (NPG) arms for 28 older rural adults (body mass index (BMI) ≥ 30 kg/m2) was conducted at a community aging center. Both groups received twice weekly physical therapist-led group strength training classes. The PG consumed a whey protein supplement three times per week, post-strength training. Primary outcomes included pre/post-fasting glucose, insulin, inflammatory markers, and homeostasis model assessment of insulin resistance (HOMA-IR). Results: Mean age and baseline BMI were 72.9 ± 4.4 years and 37.6 ± 6.9 kg/m2 in the PG and 73.0 ± 6.3 and 36.6 ± 5.5 kg/m2 in the NPG, respectively. Mean weight loss was −3.45 ± 2.86 kg in the PG and −5.79 ± 3.08 kg in the NPG (p < 0.001). There was a smaller decrease in pre- vs. post-fasting glucose levels (PG: −4 mg ± 13.9 vs. NPG: −12.2 ± 25.8 mg/dL; p = 0.10), insulin (−7.92 ± 28.08 vs. −46.7 ± 60.8 pmol/L; p = 0.01), and HOMA-IR (−0.18 ± 0.64 vs. −1.08 ± 1.50; p = 0.02) in the PG compared to the NPG. Conclusions: Protein supplementation during weight loss demonstrated a smaller decrease in insulin resistance compared to the NPG, suggesting protein may potentially mitigate beneficial effects of exercise on glucose homeostasis.
... Meanwhile, (Trommelen & van Loon, 2016) state that 40g casein protein intake 30 minutes prior to sleep, a period lacking in nutritional supply, can bring a number of advantages for recovery (Trommelen & van Loon, 2016). Research findings of (Areta et al., 2013) showed that, for recovery, 20-25g of protein (as part of a meal or snack) should be consumed every 3-5 hours in general (Areta, et al., 2013). To maximize protein synthesis, the intake of casein protein before sleeping is recommended (Res, et al., 2012). ...
... Meanwhile, (Trommelen & van Loon, 2016) state that 40g casein protein intake 30 minutes prior to sleep, a period lacking in nutritional supply, can bring a number of advantages for recovery (Trommelen & van Loon, 2016). Research findings of (Areta et al., 2013) showed that, for recovery, 20-25g of protein (as part of a meal or snack) should be consumed every 3-5 hours in general (Areta, et al., 2013). To maximize protein synthesis, the intake of casein protein before sleeping is recommended (Res, et al., 2012). ...
The aim of the study was to analyze the contribution of protein intake and exercise frequency to the cardiovascular endurance of rowing athletes in the Student Sports Education and Training Center, known as PPLP, in Kendari. The research sample consisted of 50 athletes, including 25 junior PPLP rowing athletes aged 16-19 years and 25 formers senior PPLP rowing athletes aged 25-30 years. This research included an observational study with a cross-sectional design. The collected data were analyzed using the Pearson and Spearman correlation statistics tests. The instrument for measuring protein intake was the Nutrition Adequacy Rate based on WNPG VII 2019. Exercise frequency data were obtained through interviews using a questionnaire. Cardiovascular endurance was measured by the athlete’s maximum mileage from a 15-minute running test. The results of the Spearman correlation test between exercise frequency and cardiovascular endurance showed no significant results (p 0.05). Exercise frequency had a significant positive relationship with cardiovascular endurance (p = 0.004, r = 0.395). It showed that there was a significant relationship between protein intake and cardiovascular endurance (p = 0.003, r = 0.415). The junior rowing athlete group generally had moderate cardiovascular endurance (80.0%), while the former senior rowing athlete group generally had sufficient (48.0%) and less (44.0%) cardiovascular endurance. On average, the cardiovascular endurance of the junior rowing athlete group (40.1 ml O2/kg BW/min) was higher and significantly different (p 0.05) compared to the former senior rowing athlete group (36.2 ml O2/kg BW/min). Athletes with normal protein intake (75%) had a good cardiovascular endurance. Most athletes with normal protein intake had sufficient cardiovascular endurance (45.4%). Meanwhile, the athlete with a severe protein deficiency had less cardiovascular endurance (38.4%). This study concludes that the higher the sports activity, the higher the need for protein consumption, which eventually increases the work function of the heart, especially in rowing athletes in PPLP Kendari.
... Indeed, a common proposal based on the 'refractory period' (or 'muscle full effect') of MPS (39) and that there is no inactive compartment to serve as a reservoir for protein, is that an even daily protein intake distribution across feeding events is superior to an uneven skewed distribution. However, conflicting findings have been reported from studies in older adults that have measured the response of MPS and lean mass outcomes to the manipulation of protein meal pattern (85)(86)(87)(88)(89) , with some indications that meal 1 (i.e. breakfast) is when muscle seems to be the most receptive to protein provision, as during sleep recycled AA are directed towards more critical organs and away from skeletal muscle (85)(86)(87)(88)(89) . ...
... However, conflicting findings have been reported from studies in older adults that have measured the response of MPS and lean mass outcomes to the manipulation of protein meal pattern (85)(86)(87)(88)(89) , with some indications that meal 1 (i.e. breakfast) is when muscle seems to be the most receptive to protein provision, as during sleep recycled AA are directed towards more critical organs and away from skeletal muscle (85)(86)(87)(88)(89) . Accumulating evidence, though, also suggests that bedtime protein feeding may increase overnight MPS rates and enhance skeletal muscle remodelling (90) . ...
This review explores the evolution of dietary protein intake requirements and recommendations, with a focus on skeletal muscle remodelling to support healthy ageing based on presentations at the 2023 Nutrition Society summer conference. In this review, we describe the role of dietary protein for metabolic health and ageing muscle, explain the origins of protein and amino acid (AA) requirements and discuss current recommendations for dietary protein intake, which currently sits at about 0⋅8 g/kg/d. We also critique existing (e.g. nitrogen balance) and contemporary (e.g. indicator AA oxidation) methods to determine protein/AA intake requirements and suggest that existing methods may underestimate requirements, with more contemporary assessments indicating protein recommendations may need to be increased to >1⋅0 g/kg/d. One example of evolution in dietary protein guidance is the transition from protein requirements to recommendations. Hence, we discuss the refinement of protein/AA requirements for skeletal muscle maintenance with advanced age beyond simply the dose (e.g. source, type, quality, timing, pattern, nutrient co-ingestion) and explore the efficacy and sustainability of alternative protein sources beyond animal-based proteins to facilitate skeletal muscle remodelling in older age. We conclude that, whilst a growing body of research has demonstrated that animal-free protein sources can effectively stimulate and support muscle remodelling in a manner that is comparable to animal-based proteins, food systems need to sustainably provide a diversity of both plant and animal source foods, not least for their protein content but other vital nutrients. Finally, we propose some priority research directions for the field of protein nutrition and healthy ageing.
... In addition to total protein intakes, the timing and frequency of protein feedings over the day has been shown to enhance recovery [38]. Throughout the day the body can switch between MPS and muscle protein breakdown (MPB), depending on fed and exercise states, and the aim of recovery nutrition would be to spend most of the day in a muscle-building state more so than degradation [38]. ...
... In addition to total protein intakes, the timing and frequency of protein feedings over the day has been shown to enhance recovery [38]. Throughout the day the body can switch between MPS and muscle protein breakdown (MPB), depending on fed and exercise states, and the aim of recovery nutrition would be to spend most of the day in a muscle-building state more so than degradation [38]. Evidence has shown that consuming 20-40 g of protein at a sitting, spread across 4-5 meals per day, is optimal for muscle growth and recovery [19]. ...
Golf is predominantly a skill-based sport where technical aspects are regarded as a priority area for improving performance. At present, most of the existing literature has focused on improving a player’s physicality, endurance and technical attributes in an effort to enhance performance. While important, the role of nutrition in elite golf has received little attention to date. The energy demands of the sport can vary depending on the level of the individual (recreational–professional), with distances of up to 20 km being covered and the time spent on the course ranging approximately 4–8 h each day. Like other sports, a focus on pre-game, during and post-game nutrition, including hydration, is integral to ensuring that individuals are adequately fuelled, hydrated and optimally recovered. For the elite athletes who travel extensively to international tournaments, it is important to understand the additional impact of travel on the body and consider the role nutrition can play in preventing illness and ensuring minimal disruption to golf performance. Lastly, the role of dietary supplements to enhance the performance of golfers is also important to consider. This review aims to consolidate the findings of the existing research focusing on nutrition strategies for golf performance and identify areas for potential future research.
... In people with overweight/obesity around 25 % of weight loss with daily energyrestricted diets is loss of FFM (33) . IER could lead to greater reductions in FFM for a given weight loss as a result of spontaneous decreases in physical activity during energy-restricted periods (34) , insufficient protein intakes (35) , or sub-optimal regularity of protein intake to optimise muscle protein synthesis (36) ; the latter being particularly relevant with TRE. Greater losses of FFM with energy restriction are seen amongst subjects with lower fat mass, that is, lean compared to those with overweight/obesity, men compared to Fast (no food or energy containing drinks) for 12-18 hours a day and eat normally 6-12 hours a day Usually ad-lib / normal eating in the eating window (ad-lib TRE) but can be an energy restricted diet (Energy restricted TRE). ...
Intermittent energy restricted diets are used amongst women with overweight and obesity and a healthy weight. For those with overweight and obesity weight control is typically achieved through daily energy restriction (DER) which has reduced adherence and attenuated metabolic benefits over time. Several intermittent energy restriction (IER) regimens have been developed aiming to promote maintained weight loss and additional weight independent metabolic benefits including the 5:2 diet, alternate day fasting (ADF) and time restricted eating (TRE). This review summarises the potential benefits or harms of these regimens for managing women’s health. 5:2 and ADF diets have equivalent long term (≥6-month) adherence, weight loss and metabolic benefits to DER. Current limited evidence suggests IER is a safe weight loss intervention for women which does not affect reproductive or bone health, increase eating disorders or disturb sleep. Adherence and weight loss with both IER and DER are lower amongst younger women compared to older women and men. Weight loss with ADF and TRE have respectively improved symptoms of polycystic ovarian syndrome and premenstrual syndrome but there is no evidence of weight independent effects of IER on these conditions. There is little evidence of the benefits and/or harms of IER amongst healthy weight women in whom there is a greater potential for adverse effects on reproductive and bone health, fat free mass, eating disorders and sleep. Further research benefits of IER for weight control and metabolic health as well as harms is required.
... В дополнение к количественному содержанию белка, значимую роль в поддержании мышечного здоровья и состава тела играют и другие компоненты здорового питания, включая витамины, антиоксиданты, качество белка, временной интервал его потребления, а также общее качество диеты [67][68][69][70][71]. ...
Sarcopenic obesity is a complex condition characterized by a combination of obesity and sarcopenia. This pathology has a significant impact on the health and quality of life of the elderly and old people, increasing the risk of chronic diseases and impairing physical functions. Nutritional status plays a key role in maintaining the health and functional ability of older people, influencing the development of sarcopenia and obesity. Understanding the relationship between sarcopenic obesity and nutritional status is critical for developing prevention and treatment strategies. Our scientific article covers the various mechanisms of development of sarcopenic obesity and the influence of nutritional status on sarcopenic obesity, and also examines the role of various nutrients and dietary supplements in the management of this condition. Our scientific article highlights the need for a comprehensive approach to the treatment and prevention of sarcopenic obesity among elderly and elderly patients to improve overall health and quality of life.
... g/kg body weight (or 15-25 g for most athletes) is recommended following exercise, with high-quality sources like dairy, lean meat, eggs, and soy being ideal options. [9,10] Micronutrient intake is equally critical. Iron is essential for oxygen transport, particularly for endurance athletes, with women requiring 18 mg/day and men requiring 8 mg/day. ...
Introduction Since 2019, private equity (PE) investment in sports franchises, media rights, and stadium infrastructure has grown significantly due to league bylaw changes. These assets attract PE firms with their strong returns and diversification benefits, especially in economic uncertainty. PE provides long-term value through franchise ownership, media rights monetization, and infrastructure investments. However, challenges include limited governance control and illiquid assets, complicating exit strategies. Despite this, PE remains a growing and appealing sector for investment. Materials and Methods A literature review was conducted using sources like the IMF eLibrary and PubMed, focusing on studies from 2019–2024. Keywords included “private equity,” “sport,” and “investment.” Criteria included analyses of sports financing trends and investment impacts on global markets. Results PE in sports grows yearly due to strong financial returns and diversification benefits. Challenges include governance limits and illiquidity, but PE provides liquidity and operational expertise to underfunded franchises, maximizing revenues and valuations. This aligns sports investments with macroeconomic strategies, boosting their market appeal. Conclusions Private equity's rise in sports marks a shift in financing since 2019, offering liquidity, expertise, and valuation growth. While governance challenges exist, PE investments address underfunding and position themselves as vital players in the financial evolution of professional sports.
... Omega-3s are a class of long chain polyunsaturated fatty acids known for their beneficial effects on human health [135], post-exercise protein [239], pre-sleep protein [240], protein spread [241], protein source [242,243], protein form [244][245][246], intact protein foods [247] and meal versus individual protein foods [248] such as enhanced cognitive function [187], reduced inflammatory mediators [188] and improved blood lipid profiles [189]. Most research on omega-3 fatty acids has utilised eicosapentaenoic acid (EPA)-and docosahexaenoic acid (DHA)-containing supplements, with current recommended daily intake, by the National Academy of Medicine and the Australian National Heart Foundation, being approximately 250-500 mg/day [190]. ...
Following anterior cruciate ligament (ACL) injury, quadriceps muscle atrophy persists despite rehabilitation, leading to loss of lower limb strength, osteoarthritis, poor knee joint health and reduced quality of life. However, the molecular mechanisms responsible for these deficits in hypertrophic adaptations within the quadriceps muscle following ACL injury and reconstruction are poorly understood. While resistance exercise training stimulates skeletal muscle hypertrophy, attenuation of these hypertrophic pathways can hinder rehabilitation following ACL injury and reconstruction, and ultimately lead to skeletal muscle atrophy that persists beyond ACL reconstruction, similar to disuse atrophy. Numerous studies have documented beneficial roles of nutritional support, including nutritional supplementation, in maintaining and/or increasing muscle mass. There are three main mechanisms by which nutritional supplementation may attenuate muscle atrophy and promote hypertrophy: (1) by directly affecting muscle protein synthetic machinery; (2) indirectly increasing an individual’s ability to work harder; and/or (3) directly affecting satellite cell proliferation and differentiation. We propose that nutritional support may enhance rehabilitative responses to exercise training and positively impact molecular machinery underlying muscle hypertrophy. As one of the fastest growing knee injuries worldwide, a better understanding of the potential mechanisms involved in quadriceps muscle deficits following ACL injury and reconstruction, and potential benefits of nutritional support, are required to help restore quadriceps muscle mass and/or strength. This review discusses our current understanding of the molecular mechanisms involved in muscle hypertrophy and disuse atrophy, and how nutritional supplements may leverage these pathways to maximise recovery from ACL injury and reconstruction.
... [19] Whey protein can also be consumed in the form of supplements, which has proved to enhance muscle strength, reduce fatigue, and accelerate recovery. [20], [21] Another application of whey protein is in the food packaging industry as an edible coating due to its mechanical, optical, and barrier properties in addition to its natural ability to biodegrade. [22] The physical recovery of whey protein is a complex process that has gone through many stages. ...
A significant quantity of waste is generated by food processing industries worldwide leading to severe environmental and social challenges. Within the milk processing industry, the coagulation of insoluble proteins results in the production of copious amounts of effluents. This latter yields liquid rich in soluble proteins known as whey proteins. Various techniques, including the use of organic solvents, heat treatment, and lyophilization, are employed to extract these proteins. The objective of this research is to compare the extracted substances obtained with the commercially available product. Fourier-transform infrared spectroscopy (FT-IR) is employed as the analytical technique in this study. The FT-IR spectra of the extracted whey proteins exhibit characteristic peaks similar to those reported in the literature and the commercial product. These findings validate the effectiveness of the utilized extraction methods, and further steps should be considered to enhance the yield and quality of the extracted material. The findings provided insights into the suitability and quality of the extracted substances, paving the way for improvements in the extraction process. By maximizing the utilization of waste streams from the food transformation industry, this research aims to contribute to resource optimization and sustainability in line with environmental and societal considerations.
... The remaining two doses were provided once every 3 h on two occasions (25 g of protein/placebo at +3 h and 25 g of protein/placebo at +6 h) after the game. This supplementation scheme was previously shown to optimize muscle protein synthesis over a 12 h recovery period following resistance exercise [31,32]. On practice days, supplements were consumed as a single dose (20 g of protein/placebo) after performance testing. ...
Background/objectives:
Despite being widely promoted, protein supplementation's overall effectiveness during demanding basketball schedules remains unclear. This study investigated whether increased protein intake can accelerate recovery of muscle function during a 6-day congested basketball microcycle consisting of three consecutive games while accounting for the impact of playing time.
Methods:
In a randomized, two-trial, cross-over, double-blind repeated measures design, eighteen male basketball players were assigned to a high (High PT) or a moderate (Mod PT) playing time group and participated in two trials, receiving daily either milk protein (PRO trial) or an isoenergetic amount of carbohydrates. Each trial included three consecutive games (days 1-3) and a 72 h recovery period following Game 3 (days 4-6), during which players participated in low-load practice sessions. Isometric and isokinetic peak torque of knee extensors and flexors in the dominant limb, serum creatine kinase (CK) concentration, and erythrocyte glutathione (GSH) levels were assessed prior to each game and practice session.
Results:
CK increased (p < 0.01) on game days in both groups but recovered earlier in Mod PT compared to High PT. Both eccentric and concentric peak torque was impaired (p < 0.01) up to 24-48 h post-G3 in a velocity-dependent manner. Eccentric peak torque of knee flexors at 60°/s declined to a greater extent in High PT compared to Mod PT (p < 0.01). Protein supplementation resulted in higher erythrocyte GSH concentration at pre-G2 (p < 0.05) and pre-G3 (p < 0.05) compared to placebo in both groups but did not affect any of the study outcomes.
Conclusions:
Increased protein intake during a congested basketball schedule increases erythrocyte GSH concentration but does not accelerate recovery of muscle function.
... However, this does not entirely explain the training-based differences, given that trained individuals also consumed higher relative protein intakes. Mechanistic work has shown equally distributing dietary protein boluses (∼≥20 g) throughout the day can optimize daily MPS rates compared with the same amount of protein consumed in a more typically skewed pattern (Areta et al., 2013;Mamerow et al., 2014), though long-term studies do not always confirm the assumed adaptive advantage (MacKenzie-Shalders et al., 2016). In the present work, we confirm previous findings (Gillen et al., 2017;Hone et al., 2020) that young adults consume their protein in a skewed manner, with dinner, lunch, and breakfast providing an amount of protein that likely robustly stimulates MPS . ...
We characterized daily dietary protein intakes, focusing on protein source (animal and nonanimal) and form (whole-foods and supplemental) in young (18–40 years) resistance trained (training ≥ 3×/week for ≥ 6 months; TRA; male, n = 30; female, n = 14) and recreationally active (no structured training; REC; male, n = 30; female, n = 30) individuals. Using 3-day weighed food diaries from 10 previous studies, we assessed macronutrient intakes using dietary analysis software. Energy intakes trended greater in TRA compared with REC ( p = .056) and were greater in males than females ( p = .006). TRA consumed greater ( p = .002) proportions of daily energy intake as protein than REC (23 ± 6 vs. 19 ± 5%Energy), which also trended greater in males compared with females (22 ± 3 vs. 20 ± 2%Energy; p = .060). Absolute ( p < .001) and relative (to body mass [BM]; p < .001) protein intakes were greater in TRA (males, 159 ± 54 g/day or 1.6 ± 0.7 g·kg ⁻¹ BM·day ⁻¹ ; females, 105 ± 40 g/day or 2.0 ± 0.6 g·kg ⁻¹ BM·day ⁻¹ ; p < .001) than REC (males, 103 ± 37 g/day or 1.3 ± 0.5 g·kg ⁻¹ BM·day ⁻¹ ; females, 85 ± 23 g/day or 1.3 ± 0.4 g·kg ⁻¹ BM·day ⁻¹ ; p < .001), with absolute ( p = .025), but not relative ( p = .129) intakes greater in males. A greater proportion of total protein was consumed from animal compared with nonanimal in TRA (68% vs. 32%, respectively; p < .001) and REC (64% vs. 36%, respectively; p < .001); the skew driven exclusively by males (72% vs. 28%, respectively; p < .001). A greater proportion (∼92%) of total protein was consumed as whole-foods compared with supplemental, irrespective of training status or sex ( p < .001). We show animal and whole-food–derived proteins contribute the majority to daily dietary protein intakes in TRA and REC young males and females.
... −1 for three consecutive days during energy repletion, with an increase in sodium and water on the day of competition to accentuate vascularity and muscle volume (32). The athlete consumed five protein-rich meals (0.25-0.5 g.kg −1 per meal) spaced evenly throughout the day to optimize muscle anabolism and protein balance (33). Before training, the athlete consumed a carbohydrate and protein-rich meal (~2 h before) to increase carbohydrate availability and a further 0.5 g.kg −1 of protein within 90 min of training finishing to potentiate the post-exercise muscle protein synthetic response (34). ...
Natural bodybuilding competitions involve periods of low energy availability (EA) combined with resistance training and high-protein diets to achieve extreme leanness. This study tracked a drug-free bodybuilder adopting evidence-based nutrition practices during 18 weeks of contest preparation. We measured endocrine function, resting energy expenditure, respiratory exchange ratio, body composition, resting heart rate, oral temperature, mood, and strength performance. Endocrine function was remeasured after 2 days of energy repletion. From baseline to week 18, free triiodothyronine (T3) and total testosterone (TT) fell into clinically low (2.7 pmol/L⁻¹) and sub-clinically low (9.1 nmol/L⁻¹) ranges. Resting energy expenditure decreased by −519 kcal (REEratio 0.78), and respiratory exchange ratio decreased from 0.95 to 0.85. Body mass reduced by −5.1 kg, with a sum of eight skinfold loss of −15.7 mm. Correlations were observed between body mass and decreases in oral temperature (r = 0.674, p = 0.002) and resting heart rate (r = 0.560, p = 0.016). Mood remained stable until the final 2 weeks and relative one-repetition maximum decreased in the squat (−5.4%), bench (−2.6%), and deadlift (−3.6%). Following 2 days of modest energy repletion, free T3 increased (18.5%), returning to sub-clinically low values (3.2 pmol/L⁻¹), whereas TT fell (−20.9%), reaching clinically low values (7.2 nmol/L⁻¹). These results offer insight into the dynamics of T3 and TT following a short-term period of modest energy repletion and further information on indicators of low EA during chronic energy restriction.
... The greater sensitivity of acute metabolic studies can in part be explained by the fact that such studies are typically performed under highly controlled and standardized experimental conditions, whereas long-term measurements are prone to variation due to differences in daily-life conditions between subjects. Besides consistently showing that protein ingestion augments MPS rates following resistance exercise [22,46,47], acute MPS studies have effectively been applied to define the impact of protein dose [22], protein type [48,49], and protein intake timing strategies [50] as well as different exercise training modalities [51] on MPS rates. ...
... Another explanation for the increased loss of muscle mass during intermittent fasting could be a difference in the protein intake distribution. Some studies suggest that distributing protein consumption throughout the day has a positive influence on the muscle protein synthesis [39,40]. This is due to of discovery that the anabolic effect of protein dosage is saturable [41]. ...
... Regarding timing, consumption of EAAs before, during, or immediately after exercise has been shown to enhance the anabolic response by potentiating intracellular signaling and MPS [51][52][53][54]. Greater MPS rates were also reported when protein intake was distributed evenly throughout the day (i.e., 4 x 20 g servings every 3 h) compared to less frequent higher volume servings (2 x 40 g every 6 h) [55], as is seen in the typical American dietary pattern where protein intake is heavily skewed toward the evening with a large meal [56]. ...
Obesity is a public health crisis, with prevalence rates tripling over the past 60 y. Although lifestyle modifications, such as diet and physical activity, remain the first-line treatments, recent anti-obesity medications (AOMs) have been shown to achieve greater reductions in body weight and fat mass. However, AOMs also reduce fat-free mass, including skeletal muscle, which has been demonstrated to account for 20% to 50% of total weight loss. This can equate to ∼6 kg or 10% of total lean mass after 12–18 mo, a loss comparable to a decade of human aging. Despite questions surrounding the clinical relevance of weight loss-induced muscle loss, the importance of adopting lifestyle behaviors such as eating a protein-rich diet and incorporating regular resistance training to support skeletal muscle health, long-term weight loss maintenance, and overall well-being among AOM users should be encouraged. Herein, we provide a rationale for the clinical significance of minimizing weight-loss-induced lean mass loss and emphasize the integration of diet and physical activity into AOM clinical care. Owing to a lack of published findings on diet and physical activity supporting skeletal muscle health with AOMs, specifically, we lean on findings from large-scale clinical weight loss and diet and exercise trials to draw evidence-based recommendations for strategies to protect skeletal muscle. We conclude by identifying gaps in the literature and emphasizing the need for future experimental research to optimize skeletal muscle and whole-body health through a balance of pharmacotherapy and healthy habits.
... It possesses excellent AA composition with a large content of branched-chain AA which are essential for muscle hypertrophy (Farup et al., 2014). Whey protein supplement ingestion helps to increase muscle strength, muscle mass, reduce their fatigue and fasten recovery (Areta et al., 2013). In addition, whey protein is a major source of bioactive peptides and has antihyperlipidemic, antioxidant, and antihypertensive effects (Auestad and Layman, 2021). ...
... Perhaps more important than the timing of the first protein feed relative to a RE bout is to take full advantage of the enhanced anabolic window within this 48-72 h post-exercise period with repeated protein feeds. As already highlighted, there is a refractory period in response to protein feeding following RE in young, trained individuals which is approximately 3 h in duration (86). These findings should be considered in the context of nutritional practices and recommendations, as a large proportion of the population will typically consume three protein-containing meals a day with upwards of 6 h between protein feeds, which is clearly suboptimal. ...
Protein nutrition is critical for the maintenance of skeletal muscle mass across the lifecourse and for the growth of muscle in response to resistance exercise – both acting via the stimulation of protein synthesis. The transient anabolic response to protein feeding may vary in magnitude and duration, depending on, e.g., timing, dose, amino acid composition and delivery mode, which are in turn influenced by physical activity and age. This review aims to: (i) summarise the fundamental metabolic responses of muscle to protein feeding, (ii) discuss key variables regulating muscle anabolic responses to protein feeding, and (iii) explore how these variables can be optimised for muscle anabolism in response to physical activity and ageing.
... Witard and Mettler discuss work by Areta et al. (2013) and Mallinson et al. (2023) as data to support the concept of protein intake distribution and how our recent work may not translate to trained females, respectively. For brevity, we cannot provide a more detailed discussion of the strengths and limitations of the referred work and how they relate to our recent work. ...
... It has been suggested that whey protein isolate is one of the purest sources of protein (>90% protein concentration, removed fat, removed lactose) [70]. Protein consumption is recommended at 20-30 g boluses to maximally stimulate muscle protein synthesis [51,71,72]. Many of the benefits of protein supplementation may be attributable to their essential amino acid (EAA) content. ...
The fire service suffers from high rates of cardiovascular disease and poor overall health, and firefighters often suffer fatal and non-fatal injuries while on the job. Most fatal injuries result from sudden cardiac death, while non-fatal injuries are to the musculoskeletal system. Previous works suggest a mechanistic link between several health and performance variables and injury risk. In addition, studies have suggested physical activity and nutrition can improve overall health and occupational performance. This review offers practical applications for exercise via feasible training modalities as well as nutritional recommendations that can positively impact performance on the job. Time-efficient training modalities like high-intensity interval training and feasible modalities such as resistance training offer numerous benefits for firefighters. Also, modifying and supplementing the diet and can be advantageous for health and body composition in the fire service. Firefighters have various schedules, making it difficult for planned exercise and eating while on shift. The practical training and nutritional aspects discussed in this review can be implemented on-shift to improve the overall health and performance in firefighters.
... The distribution of dietary protein intake throughout the day also represents an important consideration for optimizing protein intake in resistance-trained athletes. Prior work in this area has reported consuming a balanced distribution of protein throughout the day, consisting of 4-5 evenly spaced feedings to be optimal for maximizing post-prandial muscle protein synthesis (MPS) rates and muscle hypertrophy outcomes (12,13). ...
Background
It is unclear whether resistance training in combination with different timing of protein intake might have differential effects on muscle hypertrophy, strength, and performance. Therefore, we compared the effects of 8 weeks of resistance training combined with two different high-protein diet strategies (immediately pre-and after, or 3 h pre and after exercise) in resistance-trained males.
Methods
Forty resistance-trained males (24 ± 4 years) performed 8 weeks of resistance training combined with 2 g kg⁻¹ d⁻¹ protein. Body composition, muscular performance, and biochemical markers were assessed pre and post-intervention.
Results
Nine participants (four from 3 h group and five from the immediate group) withdrew from the study. Therefore, 31 participants completed the study. All measures of skeletal muscle mass, Australian pull-up, and muscle strength, significantly increased post-intervention in both groups (p < 0.05). The biochemical marker urea also significantly increased from pre to post in both groups (p < 0.05). There were no significant between-group differences (p > 0.05).
Conclusion
High-protein diet enhances muscular performance and skeletal muscle mass in resistance-trained males, irrespective of intake time. Consequently, the total daily protein intake appears to be the primary factor in facilitating muscle growth induced by exercise.
... The United States-Canadian dietary guidelines recommended dietary allowance (RDA) for protein intake remains the same for all adults (0.8 g/kg/d), regardless of age, with little reference to source or pattern of intake [11]. Several factors have been proposed to affect older adults' MPS response, including quantity (per-meal protein "dose") [8], quality [12], and distribution [13] of protein intake. MPS is a graded, saturable process, and the stimulation of MPS is directly related to the protein dose and subsequent aminoacidemia, reliant on essential amino acids (EAAs) and, in particular, leucine. ...
... When these inputs are optimally balanced, mTORC1 activates the downstream factors eIF4 and rpS6 (S6 ribosomal protein) to initiate MPS. These two regulatory factors serve to enhance MPS by selecting mRNAs to increase the capacity for MPS and to specifically increase the synthesis of myofibrillar proteins (17). It is important to note that the mTORC1 regulation in skeletal muscle differs from other tissues because it is sensitive to exercise (11,18). ...
The importance of meal distribution of dietary protein to optimize muscle mass and body remains unclear, and the findings are intertwined with age, physical activity, and the total quantity and quality of protein consumed. The concept of meal distribution evolved from multiple discoveries about regulating protein synthesis in skeletal muscle. The most significant was the discovery of the role of the branched-chain amino acid leucine as a metabolic signal to initiate a post-meal anabolic period of muscle protein synthesis (MPS) in older adults. Aging is often characterized by loss of muscle mass and function associated with a decline in protein synthesis. The age-related changes in protein synthesis and subsequent muscle atrophy were generally considered inevitable until the discovery of the unique role of leucine for the activation of the mTOR signal complex for the initiation of MPS. Clinical studies demonstrated that older adults (>60 years) require meals with at least 2.8 g of leucine (~30 g of protein) to stimulate MPS. This meal requirement for leucine is not observed in younger adults (<30 years), who produce a nearly linear response of MPS in proportion to the protein content of a meal. These findings suggest that while the efficiency of dietary protein to stimulate MPS declines with aging, the capacity for MPS to respond is maintained if a meal provides adequate protein. While the meal response of MPS to total protein and leucine is established, the long-term impact on muscle mass and body composition remains less clear, at least in part, because the rate of change in muscle mass with aging is small. Because direct diet studies for meal distribution during aging are impractical, research groups have applied meal distribution and the leucine threshold to protein-sparing concepts during acute catabolic conditions such as weight loss. These studies demonstrate enhanced MPS at the first meal after an overnight fast and net sparing of lean body mass during weight loss. While the anabolic benefits of increased protein at the first meal to stimulate MPS are clear, the benefits to long-term changes in muscle mass and body composition in aging adults remain speculative.
... Daily protein supplementation is associated with increased protein synthesis, [25][26][27][28][29][30][31] which may be related to reduced fatigue and soreness, 32 and a potential increase in satiety hormones and amino acids. 33 Previous studies have reported increased protein synthesis and the attenuated decline in postprandial protein synthesis with just two weeks of protein supplementation. ...
Introduction: Benefits of protein consumption are established, yet athletes often consume insufficient protein. The effect of protein supplementation timing on self- reported wellness measures (SRWM) is unknown. The purpose was to examine the effect of protein supplementation timing on overall protein intake and SRWM. Methods: Collegiate athletes (men: n=13; body mass: 76.1 ± 6.6 kg; body fat %: 14.8 ± 2.3%) (women: n=16; body mass: 72.5 ± 10.8 kg; body fat %: 24.9 ± 4.6%), defined as protein-insufficient (daily intake <1.5 g/kg body weight) participated. Protein supplementation occurred over two 2-week periods (morning, evening) separated by a 2-week washout. Daily SRWM (fatigue, soreness, sleep, stress, mood, energy, recovery, satiety) were collected. ANOVA assessed differences in total protein intake and SRWM measures across conditions. Spearman correlations assessed relationships between protein intake and SRWM.Results: No sex difference existed in protein intake based on supplementation timing. Compared to baseline, morning and evening supplementation led to an increase (p<0.05) in absolute and relative protein intake for men and women. Satiety was increased during morning and evening conditions compared to washout for men (p=0.004) and women (p=0.012), but other SRWM did not differ. Correlations existed for relative protein intake and satiety (r=0.499, p<0.001) and stress (r=-0.321, p=0.019).Conclusions: Protein supplementation enabled participants to achieve the recommended protein intake and provided a greater feeling of satiety. Satiety did not differ between morning and evening, providing flexibility as to when to ingest a daily supplement.
... Some amino acids, like alanin, are directly involved in gluconeogenesis. Others like leucine represent surrogate metabolic fuel for skeletal muscle, especially when lacking carbohydrates as a condition of restricted intake or in an insulin deficient state [71]. Even if protein catabolism minimally contributes to PA in terms of energy, correct intake of protein appears fundamental to enhancing recovery periods thus indirectly improving physical performance. ...
Type 1 diabetes mellitus (T1DM) represents a complex clinical challenge for health systems. The autoimmune destruction of pancreatic beta cells leads to a complete lack of insulin production, exposing people to a lifelong risk of acute (DKA, coma) and chronic complications (macro and microvascular). Physical activity (PA) has widely demonstrated its efficacy in helping diabetes treatment. Nutritional management of people living with T1DM is particularly difficult. Balancing macronutrients, their effects on glycemic control, and insulin treatment represents a complex clinical challenge for the diabetologist. The effects of PA on glycemic control are largely unpredictable depending on many individual factors, such as intensity, nutrient co-ingestion, and many others. Due to this clinical complexity, we have reviewed the actual scientific literature in depth to help diabetologists, sport medicine doctors, nutritionists, and all the health figures involved in diabetes care to ameliorate both glycemic control and the nutritional status of T1DM people engaging in PA. Two electronic databases (PubMed and Scopus) were searched from their inception to January 2024. The main recommendations for carbohydrate and protein ingestion before, during, and immediately after PA are explained. Glycemic management during such activity is widely reviewed. Micronutrient needs and nutritional supplement effects are also highlighted in this paper.
... It is well known that a single bout of resistance exercise in untrained volunteers increases muscle FSR above baseline up to 48 h post-exercise 16 and in trained men, alongside PRO feeding, muscle FSR is elevated up to 24 h post-exercise. 8,15,34 In addition, in trained individuals it has been shown that the magnitude of increase in MyoPS to resistance exercise and PRO feeding is similar to untrained individuals. 35 However, there are limited studies in women looking at the MPS response longer than 12 h to exercise and feeding. ...
Studies examining the effect of protein (PRO) feeding on post resistance exercise (RE) muscle protein synthesis (MPS) have primarily been performed in men, and little evidence is available regarding the quantity of PRO required to maximally stimulate MPS in trained women following repeated bouts of RE. We therefore quantified acute (4 h and 8 h) and extended (24 h) effects of two bouts of resistance exercise, alongside protein‐feeding, in women, and the PRO requirement to maximize MPS. Twenty‐four RE trained women (26.6 ± 0.7 years, mean ± SEM) performed two bouts of whole‐body RE (3 × 8 repetitions/maneuver at 75% 1‐repetition maximum) 4 h apart, with post‐exercise ingestion of 15 g, 30 g, or 60 g whey PRO (n = 8/group). Saliva, venous blood, and a vastus lateralis muscle biopsy were taken at 0 h, 4 h, 8 h, and 24 h post‐exercise. Plasma leucine and branched chain amino acids were quantified using gas chromatography mass spectrometry (GC–MS) after ingestion of D2O. Fifteen grams PRO did not alter plasma leucine concentration or myofibrillar synthetic rate (MyoFSR). Thirty and sixty grams PRO increased plasma leucine concentration above baseline (105.5 ± 5.3 μM; 120.2 ± 7.4 μM, respectively) at 4 h (151.5 ± 8.2 μM, p < 0.01; 224.8 ± 16.0 μM, p < 0.001, respectively) and 8 h (176.0 ± 7.3 μM, p < 0.001; 281.7 ± 21.6 μM, p < 0.001, respectively). Ingestion of 30 g PRO increased MyoFSR above baseline (0.068 ± 0.005%/h) from 0 to 4 h (0.140 ± 0.021%/h, p < 0.05), 0 to 8 h (0.121 ± 0.012%/h, p < 0.001), and 0 to 24 h (0.099 ± 0.011%/h, p < 0.01). Ingestion of 60 g PRO increased MyoFSR above baseline (0.063 ± 0.003%/h) from 0 to 4 h (0.109 ± 0.011%/h, p < 0.01), 0 to 8 h (0.093 ± 0.008%/h, p < 0.01), and 0 to 24 h (0.086 ± 0.006%/h, p < 0.01). Post‐exercise ingestion of 30 g or 60 g PRO, but not 15 g, acutely increased MyoFSR following two consecutive bouts of RE and extended the anabolic window over 24 h. There was no difference between the 30 g and 60 g responses.
... Although this is an approximation to the daily intake, which needs consideration when interpreting the results, this strategy should not have affected the outcome of this study. Considering protein intake in athletes, the recent focus has not only been on quantity, but also the timing of ingestion relative to exercise (Areta et al., 2013;Macnaughton et al., 2016;Res et al., 2012) to optimize recovery and muscle anabolism. The current recommendation for athletes is to consume 0.3 g·kg −1 BM·day −1 or 20-25 g of protein per meal, four to five times per day Phillips & Van Loon, 2011), some of which is likely to be consumed postexercise in the form of a snack (Abbey et al., 2017;Parnell et al., 2016;Whitehouse & Lawlis, 2017). ...
... Although this is an approximation to the daily intake, which needs consideration when interpreting the results, this strategy should not have affected the outcome of this study. Considering protein intake in athletes, the recent focus has not only been on quantity, but also the timing of ingestion relative to exercise (Areta et al., 2013;Macnaughton et al., 2016;Res et al., 2012) to optimize recovery and muscle anabolism. The current recommendation for athletes is to consume 0.3 g·kg −1 BM·day −1 or 20-25 g of protein per meal, four to five times per day Phillips & Van Loon, 2011), some of which is likely to be consumed postexercise in the form of a snack (Abbey et al., 2017;Parnell et al., 2016;Whitehouse & Lawlis, 2017). ...
... La síntesis muscular óptima sucede hasta 24 horas después del ejercicio, entonces se recomienda fraccionar la dosis proteica diaria en 3 a 5 tomas diarias (19)(20)(21)(22)(23) Consideraciones especiales en el consumo de alimentos deportivos altos en proteína (24): ...
Los alimentos deportivos y suplementos pueden tener un papel pequeño pero importante en los planes nutricionales deportivos de los atletas de alto rendimiento. Las organizaciones deportivas, los profesionales de las ciencias del deporte y de la salud y los entrenadores deberán considerar los siguientes puntos al recomendar a un deportista el uso de un suplemento o alimento deportivo: ¿su consumo es seguro?, ¿es efectivo?, ¿está permitido su uso en el deporte? Por lo anterior, el objetivo de esta guía de suplementación deportiva, adaptada del marco establecido por el Instituto Australiano del Deporte (IAD), es ofrecer información clara, resumida y actualizada acerca del uso seguro y la evidencia científica en torno a los suplementos y alimentos deportivos. El presente documento se construyó a partir del documento original “Australian Institute of Sport Position Statement. Supplements and Sports Foods in High Performance Sport” sumado a una revisión de la literatura llevada a cabo por los autores entre los meses de febrero y mayo de 2022, incluyendo ensayos clínicos aleatorizados y metaanálisis publicados en la base de datos PubMed en los últimos 10 años. Esta guía está dividida en 4 secciones según los niveles de evidencia y seguridad en su uso. El presente documento corresponde a la primera parte de la guía, que incluye los alimentos con nivel de evidencia fuerte de un efecto ergogénico y seguro para el deporte.
Objective: To evaluate the effect of administering a high-protein diet (HP) based on whey protein isolate
(WPI) associated with ST in rats.
Methods: Twenty-two Wistar rats were fed a diet containing either 14% WPI (normoproteic) or 35% WPI (high
protein) and were subjected to stair training or kept sedentary for 12 weeks. SN = sedentary normoproteic;
SH=sedentary high protein; TN = trained normoproteic; TH = trained high protein.
Results: HP decreases food intake (P < 0.0001). The SH group showed a significant reduction in plasma trigly
cerides (P = 0.03). Quadriceps weight was greatest in TH, followed by SH and TN (P < 0.0001). Kidney weight
was greater in TH, followed by SH and TN, and was greater than in SN (P < 0.0001). Urea levels were lowest
in the SN group (P < 0.001). The urinary space was larger in the TH and SH groups. HP and ST increased the
cross-sectional area (CSA) of the gastrocnemius (P < 0.0001) and quadriceps (P < 0.0001) muscles. Hepatic
glycogen deposits were highest in the SH group (P < 0.0001).
Conclusions: HP with 35% whey promoted satiety and increased hepatic glycogen content without affecting
glycemia. Its combination with ST was more efficient in increasing muscle hypertrophy, altering plasma urea
levels, and enlarging the urinary space. These findings may be related to the adaptive process of renal physi
ology stimulated by HP.
Natural boosters like methi and pumpkin seeds, increase the levels of testosterone and creatine. They benefit health and fitness by utilizing traditional herbs and nutrient-dense foods as safer and more holistic alternatives to synthetic supplements. It is reflective of a larger momentum toward sustainable, healthier lifestyle choices in avoiding synthetic products' possible side effects.
In line with emerging trends, the sports nutrition industry actively seeks cost-effective and health-promoting protein ingredients to replace animal-derived products and transition toward more sustainable practices. Protein concentrates derived from legumes, including peas, have attracted consumer interest due to their rich amino acid profiles and favourable functional properties. Our research aimed to develop and optimise an enzymatic technology for producing protein hydrolysates from locally adapted pea varieties in Kazakhstan. Based on the research findings, optimal technological conditions for protein extraction from peas via enzymatic methods were established: pea flour-to-water ratio (hydromodule) 25%; duration of water extraction 24 hours; concentration of added pepsin enzyme 4.0%; pepsin fermentation time 24 hours; concentration of added pancreatin enzyme 4.0%; pancreatin fermentation time - 5 hours. A pilot batch of enzymatically hydrolysed pea protein concentrate was produced under laboratory conditions, and analyses were performed on the resulting concentrate derived from the Aksary pea variety. The protein concentrate contained 8.92% crude protein and 5.38 ± 0.02 mg/mL amino nitrogen. Notably, due to the amino acid L-arginine at 0.540±0.216% and lysine at 0.587±0.199%, the hydrolysate can be utilised as a component of sports supplements to support muscle mass development. This work was conducted as part of the project "Development of a technology for producing protein-vitamin concentrates based on plant raw materials for sports nutrition" within the framework of the scientific-technical program BR22886613, titled "Development of Innovative technologies for the processing and storage of agricultural crop production and raw materials". The project is funded under the 267-budget program "Enhancing the accessibility of knowledge and scientific research", subprogram 101 "Program-targeted financing of scientific research and activities" of the Ministry of Agriculture of the Republic of Kazakhstan for 2024–2026.
The Dairy Academy 2024, an event held as a part of the EU Erasmus+ project ‘European Excellence in Dairy Learning’ (AEDIL Dairy CoVE), gathered 40 early career researchers with different backgrounds and from different career levels at the University of Copenhagen, Denmark on 24–28 June 2024. In the mornings, the participants engaged in interactive training sessions under the theme ‘Future Dairy Processing Challenges’, while in the afternoons, the online Dairy Science and Technology Symposium could be joined by everyone interested worldwide. On several evenings, social and networking events were offered to the participants. The event received highly positive feedback from the attendees and will be repeated with a new programme at the Agricultural University of Athens, Greece in 2025. The aim of this report is to provide a detailed summary of the summer school and symposium contents as well as an excerpt of the course evaluation to promote the upcoming Dairy Academies and inspire and guide future learning events and conferences.
Sports-related injuries have profound implications for athletes, encompassing their physical and mental health, a fact that must be acknowledged in light of the incidence of such incidents. In addition, organizations and sports federations bear significant financial burdens due to these injuries. The aforementioned expenditures comprise a wide range of medical interventions, including treatment, surgery, and the lengthy periods of rehabilitation that follow. A meticulously planned and precise nutritional plan implemented during the rehabilitation phase can substantially reduce costs by promoting speedy recovery and mitigating the likelihood of re-injuries. Protein is essential for tissue repair and preventing muscle degeneration during rehabilitation. A daily protein intake of 1.2 to 2 g/kg of body weight is strongly advised, with leucine being particularly crucial. Due to their status as the primary energy source, carbohydrates play a crucial role in facilitating the process of recovery. It is advised that approximately 3 to 5 g/kg of body weight, or 55% of caloric intake, comprise complex carbohydrates. It is crucial to emphasize that lipids should constitute approximately 20 to 25% of one's daily caloric intake. This equates to 0.8 to 2 g fat/kg of body weight per day. Empirical evidence supports the notion that integrating nourishing components into one's dietary plan, such as fish, avocado, and olive oil, is advantageous. It has been discovered that these nutrients reduce inflammation and promote tissue repair effectively. Coaches, athletes, and sports administrators can develop and implement effective nutrition programs by collaborating with sports nutrition specialists. This collaborative effort mitigates the financial strain of sports injuries while concurrently expediting the recuperation process. A balanced and concentrated dietary plan, comprising adequate quantities of protein, complex carbohydrates, and nourishing fats, is the foundation for athletes to reestablish their highest performance levels rapidly. Additionally, this dietary plan contributes to reducing recovery periods and relevant costs.
In this alphabetically arranged chapter, supplements from wallflower through zinc are discussed in detail. For each supplement, this chapter defines what it is and how it works in the body. Further, this chapter discusses the supplement’s recommended dosage as well as the evidence for or against its different usages. Safety concerns, side effects, and precautions are next discussed as well as any potential interactions with other medications. References are provided for the data provided. The goal is for the healthcare provider to be able to reference each supplement and come away with a full, balanced, evidence-based understanding of these topics.
Sarcopenia is characterized by a decline in muscle strength, generalized loss of skeletal muscle mass, and impaired physical performance, which are common outcomes used to screen, diagnose, and determine severity of sarcopenia in older adults. These outcomes are associated with poor quality of life, increased risk of falls, hospitalization, and mortality in this population. The development of sarcopenia is underpinned by aging, but other factors can lead to sarcopenia, such as chronic diseases, physical inactivity, inadequate dietary energy intake, and reduced protein intake (nutrition‐related sarcopenia), leading to an imbalance between muscle protein synthesis and muscle protein breakdown. Protein digestion and absorption are also modified with age, as well as the reduced capacity of metabolizing protein, hindering older adults from achieving ideal protein consumption (i.e., 1–1.5 g/kg/day). Nutritional supplement strategies, like animal (i.e., whey protein) and plant‐based protein, leucine, and creatine have been shown to play a significant role in improving outcomes related to sarcopenia. However, the impact of other supplements (e.g., branched‐chain amino acids, isolated amino acids, and omega‐3) on sarcopenia and related outcomes remain unclear. This narrative review will discuss the evidence of the impact of these nutritional strategies on sarcopenia outcomes in older adults.
This article pursuits to provide a comprehensive expertise of galaxy morphology, its significance in information the structure and evolution of galaxies, and the studies methodologies employed in analyzing galaxy morphology. Galaxy morphology refers to the observe of the structural characteristics and visual appearances of galaxies, which play a essential function in unraveling the formation, evolution, and dynamics of these cosmic entities. via analyzing the shapes, sizes, and spatial distributions of stars, fuel, and dust within galaxies, researchers can benefit insights into the complicated tactics that form their morphological diversity and shed light on the underlying mechanisms using galaxy evolution. this article explores the special morphological
styles of galaxies, which includes spirals, ellipticals, and irregulars, and discusses the significance of information their morphological diversity for classifying and categorizing these cosmic entities. additionally, the item highlights the function of galaxy morphology in investigating the physical techniques, including gravitational interactions, mergers, and environmental elements, that form the systems and spatial distributions of stars and gas inside galaxies. the thing also discusses the improvements in observational strategies, together with excessive-resolution imaging and spectroscopy, and the mixing of theoretical models and simulations in reading galaxy morphology. universal, this article presents precious insights into the field of galaxy morphology and its research methodologies.
Protein supplementation often refers to increasing the intake of this particular macronutrient through dietary supplements in the form of powders, ready-to-drink shakes, and bars. The primary purpose of protein supplementation is to augment dietary protein intake, aiding individuals in meeting their protein requirements, especially when it may be challenging to do so through regular food (i.e. chicken, beef, fish, pork, etc.) sources alone. A large body of evidence shows that protein has an important role in exercising and sedentary individuals. A PubMed search of "protein and exercise performance" reveals thousands of publications. Despite the considerable volume of evidence, it is somewhat surprising that several persistent questions and misconceptions about protein exist. The following are addressed: 1) Is protein harmful to your kidneys? 2) Does consuming "excess" protein increase fat mass? 3) Can dietary protein have a harmful effect on bone health? 4) Can vegans and vegetarians consume enough protein to support training adaptations? 5) Is cheese or peanut butter a good protein source? 6) Does consuming meat (i.e., animal protein) cause unfavorable health outcomes? 7) Do you need protein if you are not physically active? 8) Do you need to consume protein ≤ 1 hour following resistance training sessions to create an anabolic environment in skeletal muscle? 9) Do endurance athletes need additional protein? 10) Does one need protein supplements to meet the daily requirements of exercise-trained individuals? 11) Is there a limit to how much protein one can consume in a single meal? To address these questions, we have conducted a thorough scientific assessment of the literature concerning protein supplementation.
The proteins in our body are constantly being rebuilt, i.e. they are constantly being built up and broken down. This simultaneous synthesis and breakdown of protein forms the basis for the qualitative and quantitative maintenance of body protein, because “old” and/or damaged proteins must be continuously replaced by new ones in order to ensure protein functions. Protein synthesis and breakdown are influenced by various factors such as age, physical activity or physical activity level.
Nasogastric feeding of protein-rich liquids is a nutritional support therapy that attenuates muscle mass loss. However, whether administration via a nasogastric tube per se augments whole-body or muscle protein anabolism compared with oral administration is unknown. Healthy participants were administered a protein-rich drink (225 mL containing 21 g protein) orally (ORAL; n=13; age 21±1 yr; BMI 22.2±0.6 kg·m-2) or via a nasogastric tube (NG; 32 n=13; age 21±1 yr; BMI 23.9±0.9 kg·m-2) in a parallel group design, balanced for sex. L-[ring-2H5]-phenylalanine and L-[3,3-2H2]-tyrosine were infused to measure postabsorptive and postprandial whole-body protein turnover. Skeletal muscle biopsies were collected at -120, 0, 120 and 300 min relative to drink administration to quantify temporal myofibrillar fractional synthetic rates (myoFSR). Drink administration increased serum insulin and plasma amino acid concentrations, and to a greater extent and duration in NG versus ORAL (all interactions P<0.05). Drink administration increased whole-body protein synthesis (P<0.01), suppressed protein breakdown (P<0.001), and created positive net protein balance (P<0.001), but to a similar degree in ORAL and NG (interactions P>0.05). Drink administration increased myoFSR from the postabsorptive state (P<0.01), regardless of route of administration in ORAL and in NG (interaction P>0.05). Nasogastric bolus administration of a protein-rich drink induces insulinaemia and aminoacidaemia to a greater extent than oral administration, but the postprandial increase in whole-body protein turnover and muscle protein synthesis was equivalent between administration routes. Nasogastric administration is a potent intervention to increase postprandial amino acid availability. Future work should assess its utility in overcoming impaired sensitivity to protein feeding, such as that seen in ageing, disuse, and critical care.
Skeletal muscle protein levels are governed by the relative rates of muscle protein synthesis (MPS) and breakdown (MPB). The mechanisms controlling these rates are complex, and their integrated behaviors are challenging to study through experiments alone. The purpose of this study was to develop and analyze a kinetic model of leucine-mediated mTOR signaling and protein metabolism in the skeletal muscle of young adults. Our model amalgamates published cellular-level models of the IRS1-PI3K-Akt-mTORC1 signaling system and of skeletal-muscle leucine kinetics with physiological-level models of leucine digestion and transport and insulin dynamics. The model satisfactorily predicts experimental data from diverse leucine feeding protocols. Model analysis revealed that total levels of p70S6K are a primary determinant of MPS, insulin signaling substantially affects muscle net protein balance via its effects on MPB, and p70S6K-mediated feedback of mTORC1 signaling reduces MPS in a dose-dependent manner.
Background: Resistance exercise leads to net muscle protein accretion through a synergistic interaction of exercise and feeding. Proteins from different sources may differ in their ability to support muscle protein accretion because of different patterns of postprandial hyperaminoacidemia.
Objective: We examined the effect of consuming isonitrogenous, isoenergetic, and macronutrient-matched soy or milk beverages (18 g protein, 750 kJ) on protein kinetics and net muscle protein balance after resistance exercise in healthy young men. Our hypothesis was that soy ingestion would result in larger but transient hyperaminoacidemia compared with milk and that milk would promote a greater net balance because of lower but prolonged hyperaminoacidemia.
Design: Arterial-venous amino acid balance and muscle fractional synthesis rates were measured in young men who consumed fluid milk or a soy-protein beverage in a crossover design after a bout of resistance exercise.
Results: Ingestion of both soy and milk resulted in a positive net protein balance. Analysis of area under the net balance curves indicated an overall greater net balance after milk ingestion (P < 0.05). The fractional synthesis rate in muscle was also greater after milk consumption (0.10 ± 0.01%/h) than after soy consumption (0.07 ± 0.01%/h; P = 0.05).
Conclusions: Milk-based proteins promote muscle protein accretion to a greater extent than do soy-based proteins when consumed after resistance exercise. The consumption of either milk or soy protein with resistance training promotes muscle mass maintenance and gains, but chronic consumption of milk proteins after resistance exercise likely supports a more rapid lean mass accrual.
In this study, the interaction of mTORC1 with its downstream targets p70S6K1 and 4E-BP1 was evaluated in both mouse liver
and mouse embryonic fibroblasts following combined disruption of the genes encoding 4E-BP1 and 4E-BP2. Phosphorylation of
p70S6K1 was dramatically elevated in the livers of mice lacking 4E-BP1 and 4E-BP2 following feeding-induced activation of
mTORC1. Immunoprecipitation of mTORC1 suggested that elevated phosphorylation was the result of enhanced interaction of p70S6K1
with raptor. These findings were extended to a cell culture system wherein loss of 4E-BP1 and 4E-BP2 resulted in elevated
interaction of p70S6K1 with IGF1-induced activation of mTORC1 in conjunction with an enhanced rate of p70S6K1 phosphorylation
at Thr-389. Furthermore, cotransfecting HA-p70S6K1 with 4E-BP1, but not 4E-BP1(F114A), reduced recovery of mTORC1 in HA-p70S6K1
immunoprecipitates. Together, these findings support the conclusion that, in the absence of 4E-BP proteins, mTORC1-mediated
phosphorylation of p70S6K1 is elevated by a reduction in competition between the two substrates for interaction with raptor.
We have previously shown that the aminoacidemia caused by the consumption of a rapidly digested protein after resistance exercise enhances muscle protein synthesis (MPS) more than the amino acid (AA) profile associated with a slowly digested protein. Here, we investigated whether differential feeding patterns of a whey protein mixture commencing before exercise affect postexercise intracellular signaling and MPS.
Twelve resistance-trained males performed leg resistance exercise 45 min after commencing each of three volume-matched nutrition protocols: placebo (PLAC, artificially sweetened water), BOLUS (25 g of whey protein + 5 g of leucine dissolved in artificially sweetened water; 1× 500 mL), or PULSE (15× 33-mL aliquots of BOLUS drink every 15 min).
The preexercise rise in plasma AA concentration with PULSE was attenuated compared with BOLUS (P < 0.05); this effect was reversed after exercise, with two-fold greater leucine concentrations in PULSE compared with BOLUS (P < 0.05). One-hour postexercise, phosphorylation of p70 S6K and rpS6 was increased above baseline with BOLUS and PULSE, but not PLAC (P < 0.05); furthermore, PULSE > BOLUS (P < 0.05). MPS throughout 5 h of recovery was higher with protein ingestion compared with PLAC (0.037 ± 0.007), with no differences between BOLUS or PULSE (0.085 ± 0.013 vs. 0.095 ± 0.010%·h, respectively, P = 0.56).
Manipulation of aminoacidemia before resistance exercise via different patterns of intake of protein altered plasma AA profiles and postexercise intracellular signaling. However, there was no difference in the enhancement of the muscle protein synthetic response after exercise. Protein sources producing a slow AA release, when consumed before resistance exercise in sufficient amounts, are as effective as rapidly digested proteins in promoting postexercise MPS.
We determined the effect of muscle glycogen concentration and postexercise nutrition on anabolic signaling and rates of myofibrillar protein synthesis after resistance exercise (REX). Sixteen young, healthy men matched for age, body mass, peak oxygen uptake (Vo(2peak)) and strength (one repetition maximum; 1RM) were randomly assigned to either a nutrient or placebo group. After 48 h diet and exercise control, subjects undertook a glycogen-depletion protocol consisting of one-leg cycling to fatigue (LOW), whereas the other leg rested (NORM). The next morning following an overnight fast, a primed, constant infusion of l-[ring-(13)C(6)] phenylalanine was commenced and subjects completed 8 sets of 5 unilateral leg press repetitions at 80% 1RM. Immediately after REX and 2 h later, subjects consumed a 500 ml bolus of a protein/CHO (20 g whey + 40 g maltodextrin) or placebo beverage. Muscle biopsies from the vastus lateralis of both legs were taken at rest and 1 and 4 h after REX. Muscle glycogen concentration was higher in the NORM than LOW at all time points in both nutrient and placebo groups (P < 0.05). Postexercise Akt-p70S6K-rpS6 phosphorylation increased in both groups with no differences between legs (P < 0.05). mTOR(Ser2448) phosphorylation in placebo increased 1 h after exercise in NORM (P < 0.05), whereas mTOR increased ~4-fold in LOW (P < 0.01) and ~11 fold in NORM with nutrient (P < 0.01; different between legs P < 0.05). Post-exercise rates of MPS were not different between NORM and LOW in nutrient (0.070 ± 0.022 vs. 0.068 ± 0.018 %/h) or placebo (0.045 ± 0.021 vs. 0.049 ± 0.017 %/h). We conclude that commencing high-intensity REX with low muscle glycogen availability does not compromise the anabolic signal and subsequent rates of MPS, at least during the early (4 h) postexercise recovery period.
The nature of the deficit underlying age-related muscle wasting remains controversial. To test whether it could be due to a poor anabolic response to dietary amino acids, we measured the rates of myofibrillar and sarcoplasmic muscle protein synthesis (MPS) in 44 healthy young and old men, of similar body build, after ingesting different amounts of essential amino acids (EAA). Basal rates of MPS were indistinguishable, but the elderly showed less anabolic sensitivity and responsiveness of MPS to EAA, possibly due to decreased intramuscular expression, and activation (phosphorylation) after EAA, of amino acid sensing/signaling proteins (mammalian target of rapamycin, mTOR; p70 S6 kinase, or p70(S6k); eukaryotic initiation factor [eIF]4BP-1; and eIF2B). The effects were independent of insulin signaling since plasma insulin was clamped at basal values. Associated with the anabolic deficits were marked increases in NFkappaB, the inflammation-associated transcription factor. These results demonstrate first, EAA stimulate MPS independently of increased insulin availability; second, in the elderly, a deficit in MPS in the basal state is unlikely; and third, the decreased sensitivity and responsiveness of MPS to EAA, associated with decrements in the expression and activation of components of anabolic signaling pathways, are probably major contributors to the failure of muscle maintenance in the elderly. Countermeasures to maximize muscle maintenance should target these deficits.
Sarcopenia, the loss of skeletal muscle mass during aging, increases the risk for falls and dependency. Resistance exercise (RE) training is an effective treatment to improve muscle mass and strength in older adults, but aging is associated with a smaller amount of training-induced hypertrophy. This may be due in part to an inability to stimulate muscle-protein synthesis (MPS) after an acute bout of RE. We hypothesized that older adults would have impaired mammalian target of rapamycin complex (mTORC)1 signaling and MPS response compared with young adults after acute RE.
We measured intracellular signaling and MPS in 16 older (mean 70 ± 2 years) and 16 younger (27 ± 2 years) subjects. Muscle biopsies were sampled at baseline and at 3, 6 and 24 hr after exercise. Phosphorylation of regulatory signaling proteins and MPS were determined on successive muscle biopsies by immunoblotting and stable isotopic tracer techniques, respectively.
Increased phosphorylation was seen only in the younger group (P< 0.05) for several key signaling proteins after exercise, including mammalian target of rapamycin (mTOR), ribosomal S6 kinase (S6K)1, eukaryotic initiation factor 4E-binding protein (4E-BP)1 and extracellular signal-regulated kinase (ERK)1/2, with no changes seen in the older group (P >0.05). After exercise, MPS increased from baseline only in the younger group (P< 0.05), with MPS being significantly greater than that in the older group (P <0.05).
We conclude that aging impairs contraction-induced human skeletal muscle mTORC1 signaling and protein synthesis. These age-related differences may contribute to the blunted hypertrophic response seen after resistance-exercise training in older adults, and highlight the mTORC1 pathway as a key therapeutic target to prevent sarcopenia.
Amino acid transporters and mammalian target of rapamycin complex 1 (mTORC1) signaling are important contributors to muscle protein anabolism. Aging is associated with reduced mTORC1 signaling following resistance exercise, but the role of amino acid transporters is unknown. Young (n = 13; 28 ± 2 yr) and older (n = 13; 68 ± 2 yr) subjects performed a bout of resistance exercise. Skeletal muscle biopsies (vastus lateralis) were obtained at basal and 3, 6, and 24 h postexercise and were analyzed for amino acid transporter mRNA and protein expression and regulators of amino acid transporter transcription utilizing real-time PCR and Western blotting. We found that basal amino acid transporter expression was similar in young and older adults (P > 0.05). Exercise increased L-type amino acid transporter 1/solute-linked carrier (SLC) 7A5, CD98/SLC3A2, sodium-coupled neutral amino acid transporter 2/SLC38A2, proton-assisted amino acid transporter 1/SLC36A1, and cationic amino acid transporter 1/SLC7A1 mRNA expression in both young and older adults (P < 0.05). L-type amino acid transporter 1 and CD98 protein increased only in younger adults (P < 0.05). eukaryotic initiation factor 2 α-subunit (S52) increased similarly in young and older adults postexercise (P < 0.05). Ribosomal protein S6 (S240/244) and activating transcription factor 4 nuclear protein expression tended to be higher in the young, while nuclear signal transducer and activator of transcription 3 (STAT3) (Y705) was higher in the older subjects postexercise (P < 0.05). These results suggest that the rapid upregulation of amino acid transporter expression following resistance exercise may be regulated differently between the age groups, but involves a combination of mTORC1, activating transcription factor 4, eukaryotic initiation factor 2 α-subunit, and STAT3. We propose an increase in amino acid transporter expression may contribute to enhanced amino acid sensitivity following exercise in young and older adults. In older adults, the increased nuclear STAT3 phosphorylation may be indicative of an exercise-induced stress response, perhaps to export amino acids from muscle cells.
We previously showed that human muscle protein synthesis (MPS) increased during infusion of amino acids (AAs) and peaked at ≈120 min before returning to baseline rates, despite elevated plasma AA concentrations.
We tested whether a protein meal elicited a similar response and whether signaling responses that regulate messenger RNA translation matched MPS changes.
Eight postabsorptive healthy men (≈21 y of age) were studied during 8.5 h of primed continuous infusion of [1,2-¹³C₂]leucine with intermittent quadriceps biopsies for determination of MPS and anabolic signaling. After 2.5 h, subjects consumed 48 g whey protein.
At 45-90 min after oral protein bolus, mean (± SEM) myofibrillar protein synthesis increased from 0.03 ± 0.003% to 0.10 ± 0.01%/h; thereafter, myofibrillar protein synthesis returned to baseline rates even though plasma essential AA (EAA) concentrations remained elevated (+130% at 120 min, +80% at 180 min). The activity of protein kinase B (PKB) and phosphorylation of eukaryotic initiation factor 4G preceded the rise of MPS and increases in phosphorylation of ribosomal protein kinase S6 (S6K1), and 4E-binding protein 1 (4EBP1) was superimposable with MPS responses until 90 min. However, although MPS decreased thereafter, all signals, with the exception of PKB activity (which mirrored insulin responses), remained elevated, which echoed the slowly declining plasma EAA profile. The phosphorylation of eukaryotic initiation factor 2α increased only at 180 min. Thus, discordance existed between MPS and the mammalian target of rapamycin complex 1 (mTORC1) and signaling (ie, S6K1 and 4EBP1 phosphorylation).
We confirm our previous findings that MPS responses to AAs are transient, even with oral protein bolus. However, changes in MPS only reflect elevated mTORC1 signaling during the upswing in MPS.
Regular performance of resistance exercise induces an increase in skeletal muscle mass, however, the molecular mechanisms underlying this effect are not yet fully understood. The purpose of the present investigation was to examine acute changes in molecular signalling in response to resistance exercise involving different training volumes. Eight untrained male subjects carried out one, three and five sets of 6 repetition maximum (RM) in leg press exercise in a random order. Muscle biopsies were taken from the vastus lateralis both prior to and 30 min after each training session and the effect on protein signalling was studied. Phosphorylation of Akt was not altered significantly after any of the training protocols, whereas that of the mammalian target of rapamycin was enhanced to a similar extent by training at all three volumes. The phosphorylation of p70S6 kinase (p70(S6k)) was elevated threefold after 3 × 6 RM and sixfold after 5 × 6 RM, while the phosphorylation of S6 was increased 30- and 55-fold following the 3 × 6 RM and 5 × 6 RM exercises, respectively. Moreover, the level of the phosphorylated form of the gamma isoform of p38 MAPK was enhanced three to fourfold following each of the three protocols, whereas phosphorylation of ERK1/2 was unchanged 30 min following exercise. These findings indicate that when exercise is performed in a fasted state, the increase in phosphorylation of signalling molecules such as p70(S6k) and the S6 ribosomal protein in human muscle depends on the exercise volume.
We aimed to determine if any mechanistic differences exist between a single set (1SET) and multiple sets (i.e. 3 sets; 3SET) of resistance exercise by utilizing a primed constant infusion of [ring-13C6]phenylalanine to determine myofibrillar protein synthesis (MPS) and Western blot analysis to examine anabolic signalling molecule phosphorylation following an acute bout of resistance exercise. Eight resistance-trained men (24+/-5 years, BMI=25+/-4 kg m2) were randomly assigned to perform unilateral leg extension exercise at 70% concentric one repetition maximum (1RM) until volitional fatigue for 1SET or 3SET. Biopsies from the vastus lateralis were taken in the fasted state (Fast) and fed state (Fed; 20 g of whey protein isolate) at rest, 5 h Fed, 24 h Fast and 29 h Fed post-exercise. Fed-state MPS was transiently elevated above rest at 5 h for 1SET (2.3-fold) and returned to resting levels by 29 h post-exercise. However, the exercise induced increase in MPS following 3SET was superior in amplitude and duration as compared to 1SET at both 5 h (3.1-fold above rest) and 29 h post-exercise (2.3-fold above rest). Phosphorylation of 70 kDa S6 protein kinase (p70S6K) demonstrated a coordinated increase with MPS at 5 h and 29 h post-exercise such that the extent of p70S6K phosphorylation was related to the MPS response (r=0.338, P=0.033). Phosphorylation of 90 kDa ribosomal S6 protein kinase (p90RSK) and ribosomal protein S6 (rps6) was similar for 1SET and 3SET at 24 h Fast and 29 h Fed, respectively. However, 3SET induced a greater activation of eukaryotic translation initiation factor 2B (eIF2B) and rpS6 at 5 h Fed. These data suggest that 3SET of resistance exercise is more anabolic than 1SET and may lead to greater increases in myofibrillar protein accretion over time.
Essential amino acids (EAA) stimulate skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis. It has recently been reported that an increase in amino acid (AA) transporter expression during anabolic conditions is rapamycin-sensitive. The purpose of this study was to determine whether an increase in EAA availability increases AA transporter expression in human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis of seven young adult subjects (3 male, 4 female) before and 1-3 h after EAA ingestion (10 g). Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques. Quantitative RT-PCR, and immunoblotting were used to determine the mRNA and protein expression, respectively, of AA transporters and members of the general AA control pathway [general control nonrepressed (GCN2), activating transcription factor (ATF4), and eukaryotic initiation factor (eIF2) alpha-subunit (Ser(52))]. EAA ingestion increased blood leucine concentration, delivery of leucine to muscle, transport of leucine from blood into muscle, intracellular muscle leucine concentration, ribosomal protein S6 (Ser(240/244)) phosphorylation, and muscle protein synthesis. This was followed with increased L-type AA transporter (LAT1), CD98, sodium-coupled neutral AA transporter (SNAT2), and proton-coupled amino acid transporter (PAT1) mRNA expression at 1 h (P < 0.05) and modest increases in LAT1 protein expression (3 h post-EAA) and SNAT2 protein expression (2 and 3 h post-EAA, P < 0.05). Although there were no changes in GCN2 expression and eIF2 alpha phosphorylation, ATF4 protein expression reached significance by 2 h post-EAA (P < 0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle AA transporter expression, perhaps in an mTORC1-dependent manner, which may be an adaptive response necessary for improved AA intracellular delivery.
The mammalian target of rapamycin (mTOR) is a highly conserved atypical serinethreonine kinase that controls numerous functions essential for cell homeostasis and adaptation in mammalian cells via 2 distinct protein complex formations. Moreover, mTOR is a key regulatory protein in the insulin signalling cascade and has also been characterized as an insulin-independent nutrient sensor that may represent a critical mediator in obesity-related impairments of insulin action in skeletal muscle. Exercise characterizes a remedial modality that enhances mTOR activity and subsequently promotes beneficial metabolic adaptation in skeletal muscle. Thus, the metabolic effects of nutrients and exercise have the capacity to converge at the mTOR protein complexes and subsequently modify mTOR function. Accordingly, the aim of the present review is to highlight the role of mTOR in the regulation of insulin action in response to overnutrition and the capacity for exercise to enhance mTOR activity in skeletal muscle.
Dietary Guidelines for Americans provide nutrition advice aimed at promoting healthy dietary choices for life-long health and reducing risk of chronic diseases. With the advancing age of the population, the 2010 Dietary Guidelines confront increasing risks for age-related problems of obesity, osteoporosis, type 2 diabetes, Metabolic Syndrome, heart disease, and sarcopenia. New research demonstrates that the meal distribution and amount of protein are important in maintaining body composition, bone health and glucose homeostasis. This editorial reviews the benefits of dietary protein for adult health, addresses omissions in current nutrition guidelines, and offers concepts for improving the Dietary Guidelines.
The purpose of this study was to investigate the magnitude and time course for changes in muscle protein synthesis (MPS) after a single bout of resistance exercise. Two groups of six male subjects performed heavy resistance exercise with the elbow flexors of one arm while the opposite arm served as a control. MPS from exercised (ex) and control (con) biceps brachii was assessed 4 (group A) and 24 h (group B) postexercise by the increment in L-[1-13C]leucine incorporation into muscle biopsy samples. In addition, RNA capacity and RNA activity were determined to assess whether transcriptional and/or translational processes affected MPS. MPS was significantly elevated in biceps of the ex compared with the con arms of both groups (group A, ex 0.1007 +/- 0.0330 vs. con 0.067 +/- 0.0204%/h; group B ex 0.0944 +/- 0.0363 vs. con 0.0452 +/- 0.0126%/h). RNA capacity was unchanged in the ex biceps of both groups relative to the con biceps, whereas RNA activity was significantly elevated in the ex biceps of both groups (group A, ex 0.19 +/- 0.10 vs. con 0.12 +/- 0.05 micrograms protein.h-1.microgram-1 total RNA; group B, ex 0.18 +/- 0.06 vs. con 0.08 +/- 0.02 micrograms protein.h-1.microgram-1 total RNA). The results indicate that a single bout of heavy resistance exercise can increase biceps MPS for up to 24 h postexercise. In addition, these increases appear to be due to changes in posttranscriptional events.
1. Measurements have been made of whole-body and skeletal muscle protein synthesis in fed and fasted adults with l-[1-13C]leucine.
2. The marked increase in whole-body synthesis on feeding largely reflects the changes in protein synthesis in muscle, which doubles on feeding, compared with a 40% increase in that of the rest of the body.
3. Skeletal muscle in fed man contributes more than half to total protein synthesis occurring in the whole body.
High-resistance exercise training results in an increase in muscle wet mass and protein content. To begin to address the acute changes following a single bout of high-resistance exercise, a new model has been developed. Training rats twice a week for 6 wk resulted in 13.9 and 14.4% hypertrophy in the extensor digitorum longus (EDL) and tibialis anterior (TA) muscles, respectively. Polysome profiles after high-resistance lengthening contractions suggest that the rate of initiation is increased. The activity of the 70-kDa S6 protein kinase (p70(S6k)), a regulator of translation initiation, is also increased following high-resistance lengthening contractions (TA, 363 +/- 29%; EDL, 353 +/- 39%). Furthermore, the increase in p70(S6k) activity 6 h after exercise correlates with the percent change in muscle mass after 6 wk of training (r = 0.998). The tight correlation between the activation of p70(S6k) and the long-term increase in muscle mass suggests that p70(S6k) phosphorylation may be a good marker for the phenotypic changes that characterize muscle hypertrophy and may play a role in load-induced skeletal muscle growth.
The purpose of this study was to determine if the acute anabolic muscle response to resistance exercise and essential amino acids (EAA) reflects the response over 24 h. Seven subjects participated in the following two 24-h studies: 1) resting (REST) and 2) rest plus resistance exercise and consumption of EAA (ES). Net balance (NB) across the leg was determined for four amino acids. [(13)C(6)]phenylalanine was infused to determine mixed muscle fractional synthetic rate (FSR). Twenty-four-hour FSR was significantly greater for ES than for REST (P = 0.003). Exchange of phenylalanine across the leg was -194 +/- 74 (SE) mg for ES and -371 +/- 88 mg for REST (P = 0.07) over 24 h and 229 +/- 42 mg (ES) and 28 +/- 15 mg (REST; P < 0.01) over 3 h corresponding to exercise and EAA consumption for ES. The difference in phenylalanine exchange between REST and ES was not different for measurements over 24 and 3 h. Increases in NB during ES were primarily the result of increases in protein synthesis. Results for other amino acids were similar. The acute anabolic response of muscle to EAA intake and exercise is additive to the response at rest and thus reflects the 24-h response.
The nature of the deficit underlying age-related muscle wasting remains controversial. To test whether it could be due to a poor anabolic response to dietary amino acids, we measured the rates of myofibrillar and sarcoplasmic muscle protein synthesis (MPS) in 44 healthy young and old men, of similar body build, after ingesting different amounts of essential amino acids (EAA). Basal rates of MPS were indistinguishable, but the elderly showed less anabolic sensitivity and responsiveness of MPS to EAA, possibly due to decreased intramuscular expression, and activation (phosphorylation) after EAA, of amino acid sensing/signaling proteins (mammalian target of rapamycin, mTOR; p70 S6 kinase, or p70(S6k); eukaryotic initiation factor [eIF]4BP-1; and eIF2B). The effects were independent of insulin signaling since plasma insulin was clamped at basal values. Associated with the anabolic deficits were marked increases in NFkappaB, the inflammation-associated transcription factor. These results demonstrate first, EAA stimulate MPS independently of increased insulin availability; second, in the elderly, a deficit in MPS in the basal state is unlikely; and third, the decreased sensitivity and responsiveness of MPS to EAA, associated with decrements in the expression and activation of components of anabolic signaling pathways, are probably major contributors to the failure of muscle maintenance in the elderly. Countermeasures to maximize muscle maintenance should target these deficits.
Physiologically important cell-signalling networks are complex, and contain several points of regulation, signal divergence and crosstalk with other signalling cascades. Here, we use the concept of 'critical nodes' to define the important junctions in these pathways and illustrate their unique role using insulin signalling as a model system.
... Moreover, by promoting Akt-mediated glucose uptake, mTORC2 fuels the metabolism of cancer cells. ... loops to counteract the action of rapamycin, dampening its effectiveness in cancer models and ... of rapamycin or its prolonged delivery can block mTORC2 in some cell lines 20 ...
• The aim of this study was to describe the time course of the response of human muscle protein synthesis (MPS) to a square wave increase in availability of amino acids (AAs) in plasma. We investigated the responses of quadriceps MPS to a ≈1.7-fold increase in plasma AA concentrations using an intravenous infusion of 162 mg (kg body weight)−1 h−1 of mixed AAs. MPS was estimated from D3-leucine labelling in protein after a primed, constant intravenous infusion of D3-ketoisocaproate, increased appropriately during AA infusion. • Muscle was separated into myofibrillar, sarcoplasmic and mitochondrial fractions. MPS, both of mixed muscle and of fractions, was estimated during a basal period (2.5 h) and at 0.5-4 h intervals for 6 h of AA infusion. • Rates of mixed MPS were not significantly different from basal (0.076 ± 0.008 % h−1) in the first 0.5 h of AA infusion but then rose rapidly to a peak after 2 h of ≈2.8 times the basal value. Thereafter, rates declined rapidly to the basal value. All muscle fractions showed a similar pattern. • The results suggest that MPS responds rapidly to increased availability of AAs but is then inhibited, despite continued AA availability. These results suggest that the fed state accretion of muscle protein may be limited by a metabolic mechanism whenever the requirement for substrate for protein synthesis is exceeded.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-DeltaDeltaCr) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-DeltaDeltaCr) method. In addition, we present the derivation and applications of two variations of the 2(-DeltaDeltaCr) method that may be useful in the analysis of real-time, quantitative PCR data. (C) 2001 Elsevier science.
Key points
Essential amino acids (EAAs) stimulate increased rates of myofibrillar protein synthesis (MPS).
Leucine is a key regulator of MPS in rodents; however, its importance relative to the other EAAs is not clear.
About 20 g of protein maximally stimulates MPS after resistance exercise in young men, but we do not know if smaller doses can be made better by adding certain amino acids.
We report that a suboptimal dose of whey protein (6.25 g) supplemented with either leucine or a mixture of EAAs without leucine stimulates MPS similar to 25 g of whey protein under resting conditions; however, only 25 g of whey sustains exercise‐induced rates of MPS.
Adding leucine or a mixture of EAAs without leucine to a suboptimal dose of whey is as effective as 25 g whey at stimulating fed rates of MPS; however, 25 g of whey is better suited to increase resistance exercise‐induced muscle anabolism.
We made sex-based comparisons of rates of myofibrillar protein synthesis (MPS) and anabolic signaling after a single bout of high-intensity resistance exercise. Eight men (20 ± 10 yr, BMI = 24.3 ± 2.4) and eight women (22 ± 1.8 yr, BMI = 23.0 ± 1.9) underwent primed constant infusions of l-[ring-(13)C(6)]phenylalanine on consecutive days with serial muscle biopsies. Biopsies were taken from the vastus lateralis at rest and 1, 3, 5, 24, 26, and 28 h after exercise. Twenty-five grams of whey protein was ingested immediately and 26 h after exercise. We also measured exercise-induced serum testosterone because it is purported to contribute to increases in myofibrillar protein synthesis (MPS) postexercise and its absence has been hypothesized to attenuate adaptative responses to resistance exercise in women. The exercise-induced area under the testosterone curve was 45-fold greater in men than women in the early (1 h) recovery period following exercise (P < 0.001). MPS was elevated similarly in men and women (2.3- and 2.7-fold, respectively) 1-5 h postexercise and after protein ingestion following 24 h recovery. Phosphorylation of mTOR(Ser2448) was elevated to a greater extent in men than women acutely after exercise (P = 0.003), whereas increased phosphorylation of p70S6K1(Thr389) was not different between sexes. Androgen receptor content was greater in men (main effect for sex, P = 0.049). Atrogin-1 mRNA abundance was decreased after 5 h recovery in both men and women (P < 0.001), and MuRF-1 expression was elevated in men after protein ingestion following 24 h recovery (P = 0.003). These results demonstrate minor sex-based differences in signaling responses and no difference in the MPS response to resistance exercise in the fed state. Interestingly, our data demonstrate that exercise-induced increases in MPS are dissociated from postexercise testosteronemia and that stimulation of MPS occurs effectively with low systemic testosterone concentrations in women.
Whey protein ingestion has been shown to effectively stimulate postprandial muscle protein accretion in older adults. However, the impact of the amount of whey protein ingested on protein digestion and absorption kinetics, whole body protein balance, and postprandial muscle protein accretion remains to be established. We aimed to fill this gap by including 33 healthy, older men (73 ± 2 yr) who were randomly assigned to ingest 10, 20, or 35 g of intrinsically l-[1-¹³C]phenylalanine-labeled whey protein (n = 11/treatment). Ingestion of labeled whey protein was combined with continuous intravenous l-[ring-²H₅]phenylalanine and l-[ring-²H₂]tyrosine infusion to assess the metabolic fate of whey protein-derived amino acids. Dietary protein digestion and absorption rapidly increased following ingestion of 10, 20, and 35 g whey protein, with the lowest and highest (peak) values observed following 10 and 35 g, respectively (P < 0.05). Whole body net protein balance was positive in all groups (19 ± 1, 37 ± 2, and 58 ± 2 μmol/kg), with the lowest and highest values observed following ingestion of 10 and 35 g, respectively (P < 0.05). Postprandial muscle protein accretion, assessed by l-[1-¹³C]phenylalanine incorporation in muscle protein, was higher following ingestion of 35 g when compared with 10 (P < 0.01) or 20 (P < 0.05) g. We conclude that ingestion of 35 g whey protein results in greater amino acid absorption and subsequent stimulation of de novo muscle protein synthesis compared with the ingestion of 10 or 20 g whey protein in healthy, older men.
Opinion on the role of protein in promoting athletic performance is divided along the lines of how much aerobic-based versus resistance-based activity the athlete undertakes. Athletes seeking to gain muscle mass and strength are likely to consume higher amounts of dietary protein than their endurance-trained counterparts. The main belief behind the large quantities of dietary protein consumption in resistance-trained athletes is that it is needed to generate more muscle protein. Athletes may require protein for more than just alleviation of the risk for deficiency, inherent in the dietary guidelines, but also to aid in an elevated level of functioning and possibly adaptation to the exercise stimulus. It does appear, however, that there is a good rationale for recommending to athletes protein intakes that are higher than the RDA. Our consensus opinion is that leucine, and possibly the other branched-chain amino acids, occupy a position of prominence in stimulating muscle protein synthesis; that protein intakes in the range of 1.3-1.8 g · kg(-1) · day(-1) consumed as 3-4 isonitrogenous meals will maximize muscle protein synthesis. These recommendations may also be dependent on training status: experienced athletes would require less, while more protein should be consumed during periods of high frequency/intensity training. Elevated protein consumption, as high as 1.8-2.0 g · kg(-1) · day(-1) depending on the caloric deficit, may be advantageous in preventing lean mass losses during periods of energy restriction to promote fat loss.
Resistance exercise and amino acids are two major factors that influence muscle protein turnover. Here, we examined the effects of resistance exercise and branched-chain amino acids (BCAA), individually and in combination, on the expression of anabolic and catabolic genes in human skeletal muscle. Seven subjects performed two sessions of unilateral leg press exercise with randomized supplementation with BCAA or flavored water. Biopsies were collected from the vastus lateralis muscle of both the resting and exercising legs before and repeatedly after exercise to determine levels of mRNA, protein phosphorylation, and amino acid concentrations. Intake of BCAA reduced (P < 0.05) MAFbx mRNA by 30 and 50% in the resting and exercising legs, respectively. The level of MuRF-1 mRNA was elevated (P < 0.05) in the exercising leg two- and threefold under the placebo and BCAA conditions, respectively, whereas MuRF-1 total protein increased by 20% (P < 0.05) only in the placebo condition. Phosphorylation of p70(S6k) increased to a larger extent (∼2-fold; P < 0.05) in the early recovery period with BCAA supplementation, whereas the expression of genes regulating mTOR activity was not influenced by BCAA. Muscle levels of phenylalanine and tyrosine were reduced (13-17%) throughout recovery (P < 0.05) in the placebo condition and to a greater extent (32-43%; P < 0.05) following BCAA supplementation in both resting and exercising muscle. In conclusion, BCAA ingestion reduced MAFbx mRNA and prevented the exercise-induced increase in MuRF-1 total protein in both resting and exercising leg. Further-more, resistance exercise differently influenced MAFbx and MuRF-1 mRNA expression, suggesting both common and divergent regulation of these two ubiquitin ligases.
We aimed to determine if the time that muscle is under loaded tension during low intensity resistance exercise affects the synthesis of specific muscle protein fractions or phosphorylation of anabolic signalling proteins. Eight men (24 ± 1 years (sem), BMI = 26.5 ± 1.0 kg m(-2)) performed three sets of unilateral knee extension exercise at 30% of one-repetition maximum strength involving concentric and eccentric actions that were 6 s in duration to failure (SLOW) or a work-matched bout that consisted of concentric and eccentric actions that were 1 s in duration (CTL). Participants ingested 20 g of whey protein immediately after exercise and again at 24 h recovery. Needle biopsies (vastus lateralis) were obtained while fasted at rest and after 6, 24 and 30 h post-exercise in the fed-state following a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine. Myofibrillar protein synthetic rate was higher in the SLOW condition versus CTL after 24-30 h recovery (P < 0.001) and correlated to p70S6K phosphorylation (r = 0.42, P = 0.02). Exercise-induced rates of mitochondrial and sarcoplasmic protein synthesis were elevated by 114% and 77%, respectively, above rest at 0-6 h post-exercise only in the SLOW condition (both P < 0.05). Mitochondrial protein synthesis rates were elevated above rest during 24-30 h recovery in the SLOW (175%) and CTL (126%) conditions (both P < 0.05). Lastly, muscle PGC-1α expression was increased at 6 h post-exercise compared to rest with no difference between conditions (main effect for time, P < 0.001). These data show that greater muscle time under tension increased the acute amplitude of mitochondrial and sarcoplasmic protein synthesis and also resulted in a robust, but delayed stimulation of myofibrillar protein synthesis 24-30 h after resistance exercise.
Ingestion of whey or casein yields divergent patterns of aminoacidemia that influence whole-body and skeletal muscle myofibrillar protein synthesis (MPS) after exercise. Direct comparisons of the effects of contrasting absorption rates exhibited by these proteins are confounded by their differing amino acid contents.
Our objective was to determine the effect of divergent aminoacidemia by manipulating ingestion patterns of whey protein alone on MPS and anabolic signaling after resistance exercise.
In separate trials, 8 healthy men consumed whey protein either as a single bolus (BOLUS; 25-g dose) or as repeated, small, "pulsed" drinks (PULSE; ten 2.5-g drinks every 20 min) to mimic a more slowly digested protein. MPS and phosphorylation of signaling proteins involved in protein synthesis were measured at rest and after resistance exercise.
BOLUS increased blood essential amino acid (EAA) concentrations above those of PULSE (162% compared with 53%, P < 0.001) 60 min after exercise, whereas PULSE resulted in a smaller but sustained increase in aminoacidemia that remained elevated above BOLUS amounts later (180-220 min after exercise, P < 0.05). Despite an identical net area under the EAA curve, MPS was elevated to a greater extent after BOLUS than after PULSE early (1-3 h: 95% compared with 42%) and later (3-5 h: 193% compared with 121%) (both P < 0.05). There were greater changes in the phosphorylation of the Akt-mammalian target of rapamycin pathway after BOLUS than after PULSE.
Rapid aminoacidemia in the postexercise period enhances MPS and anabolic signaling to a greater extent than an identical amount of protein fed in small pulses that mimic a more slowly digested protein. A pronounced peak aminoacidemia after exercise enhances protein synthesis. This trial was registered at clinicaltrials.gov as NCT01319513.
Non-technical summary A single bout of exercise stimulates the production of new muscle proteins. Furthermore, ingesting protein in close proximity to exercise enhances the metabolic response. Long-term exercise training promotes muscle adaptation, and the mode of exercise performed determines the type of proteins that are made. To date, the types of proteins that are made when protein is ingested after endurance exercise are not known. We report that when well-trained male cyclists ingest protein with a carbohydrate drink after a high-intensity ride, production of proteins responsible for muscle contraction is increased. Proteins responsible for aerobic energy production are not responsive to protein feeding. Furthermore, specific signals within the muscle that control protein synthesis are responsive to protein ingestion, providing a potential mechanism to underpin our primary findings. These results suggest that protein feeding after intense endurance exercise may be important in maintaining the structural quality and power generating capacity of the muscle.
We aimed to determine whether an exercise-mediated enhancement of muscle protein synthesis to feeding persisted 24 h after resistance exercise. We also determined the impact of different exercise intensities (90% or 30% maximal strength) or contraction volume (work-matched or to failure) on the response at 24 h of recovery. Fifteen men (21 ± 1 y, BMI = 24.1 ± 0.8 kg · m(-2)) received a primed, constant infusion of l-[ring-(13)C(6)]phenylalanine to measure muscle protein synthesis after protein feeding at rest (FED; 15 g whey protein) and 24 h after resistance exercise (EX-FED). Participants performed unilateral leg exercises: 1) 4 sets at 90% of maximal strength to failure (90FAIL); 2) 30% work-matched to 90FAIL (30WM); or 3) 30% to failure (30FAIL). Regardless of condition, rates of mixed muscle protein and sarcoplasmic protein synthesis were similarly stimulated at FED and EX-FED. In contrast, protein ingestion stimulated rates of myofibrillar protein synthesis above fasting rates by 0.016 ± 0.002%/h and the response was enhanced 24 h after resistance exercise, but only in the 90FAIL and 30FAIL conditions, by 0.038 ± 0.012 and 0.041 ± 0.010, respectively. Phosphorylation of protein kinase B on Ser473 was greater than FED at EX-FED only in 90FAIL, whereas phosphorylation of mammalian target of rapamycin on Ser2448 was significantly increased at EX-FED above FED only in the 30FAIL condition. Our results suggest that resistance exercise performed until failure confers a sensitizing effect on human skeletal muscle for at least 24 h that is specific to the myofibrillar protein fraction.
The effect of nutrient availability on the acute molecular responses following repeated sprint exercise is unknown. The aim of this study was to determine skeletal muscle cellular and protein synthetic responses following repeated sprint exercise with nutrient provision. Eight healthy young male subjects undertook two sprint cycling sessions (10 × 6 s, 0.75 N m torque kg(-1), 54 s recovery) with either pre-exercise nutrient (24 g whey, 4.8 g leucine, 50 g maltodextrin) or non-caloric placebo ingestion. Muscle biopsies were taken from vastus lateralis at rest, and after 15 and 240 min post-exercise recovery to determine muscle cell signalling responses and protein synthesis by primed constant infusion of L: -[ring-(13)C(6)] phenylalanine. Peak and mean power outputs were similar between nutrient and placebo trials. Post-exercise myofibrillar protein synthetic rate was greater with nutrient ingestion compared with placebo (~48%, P < 0.05) but the rate of mitochondrial protein synthesis was similar between treatments. The increased myofibrillar protein synthesis following sprints with nutrient ingestion was associated with coordinated increases in Akt-mTOR-S6K-rpS6 phosphorylation 15 min post-exercise (~200-600%, P < 0.05), while there was no effect on these signalling molecules when exercise was undertaken in the fasted state. For the first time we report a beneficial effect of nutrient provision on anabolic signalling and muscle myofibrillar protein synthesis following repeated sprint exercise. Ingestion of protein/carbohydrate in close proximity to high-intensity sprint exercise provides an environment that increases cell signalling and protein synthesis.
In all eukaryotes, the target of rapamycin (TOR) signalling pathway couples energy
and nutrient abundance to the execution of cell growth and division, owing to the ability of TOR protein kinase to simultaneously sense energy, nutrients and stress and, in metazoans, growth factors. Mammalian TOR complex 1 (mTORC1) and mTORC2 exert their actions by regulating other important kinases, such as S6 kinase (S6K) and Akt. In the past few years, a significant advance in our understanding of the regulation and functions of mTOR has revealed the crucial involvement of this signalling pathway in the onset and progression of diabetes, cancer and ageing.
Feeding protein after resistance exercise enhances the magnitude and duration of myofibrillar protein synthesis (MPS) over that induced by feeding alone. We hypothesized that the underlying mechanism for this would be a greater and prolonged phosphorylation of signalling involved in protein translation.
Seven healthy young males performed unilateral resistance exercise followed immediately by the ingestion of 25 g of whey protein to maximally stimulate MPS in a rested and exercised leg.
Phosphorylation of p70 ribosomal protein S6 kinase (p70S6K) was elevated (P<0.05) above fasted at 1 h at rest whereas it was elevated at 1, 3 and 5 h after exercise with protein ingestion and displayed a similar post-exercise time course to that shown by MPS. Extracellular regulated kinase1/2 (ERK1/2) and p90 ribosomal S6 kinase (p90RSK) phosphorylation were unaltered after protein ingestion at rest but were elevated (P < 0.05) above fasted early in recovery (1 h) and were greater for the exercised-fed leg than feeding alone (main effect; P < 0.01). Eukaryotic elongation factor 2 (eEF2) phosphorylation was also less (main effect; P<0.05) in the exercised-fed leg than in the rested leg suggesting greater activity after exercise. Eukaryotic initiation 4E binding protein-1 (4EBP-1) phosphorylation was increased (P<0.05) above fasted to the same extent in both conditions.
Our data suggest that resistance exercise followed by protein feeding stimulates MPS over that induced by feeding alone in part by enhancing the phosphorylation of select proteins within the mammalian target of rapamycin (p70S6K, eEF2) and by activating proteins within the mitogen-activated protein kinase (ERK1/2, p90RSK) signalling.
The aim of this study was to determine the early time course of exercise-induced signaling after divergent contractile activity associated with resistance and endurance exercise.
Sixteen male subjects were randomly assigned to either a cycling (CYC; n = 8, 60 min, 70% V˙O2peak) or resistance (REX; n = 8, 8 x 5 leg extension, 80% one-repetition maximum, 3-min recovery) exercise group. Serial muscle biopsies were obtained from vastus lateralis at rest before, immediately after, and after 15, 30, and 60 min of passive recovery to determine early signaling responses after exercise.
There were comparable increases from rest in Akt(Thr308/Ser473) and mTOR(Ser2448) phosphorylation during the postexercise time course that peaked 30-60 min after both CYC and REX (P < 0.05). There were also similar patterns in p70S6K(Thr389) and 4E-BP1(Thr37/46) phosphorylation, but a greater magnitude of effect was observed for REX and CYC, respectively (P < 0.05). However, AMPK(Thr172) phosphorylation was only significantly elevated after CYC (P < 0.05), and we observed divergent responses for glycogen synthase(Ser641) and AS160 phosphorylation that were enhanced after CYC but not REX (P < 0.05).
We show a similar time course for Akt-mTOR-S6K phosphorylation during the initial 60-min recovery period after divergent contractile stimuli. Conversely, enhanced phosphorylation status of proteins that promote glucose transport and glycogen synthesis only occurred after endurance exercise. Our results indicate that endurance and resistance exercise initiate translational signaling, but high-load, low-repetition contractile activity failed to promote phosphorylation of pathways regulating glucose metabolism.
We aimed to determine whether there is a differential stimulation of the contractile myofibrillar and the cellular sarcoplasmic proteins after ingestion of protein and how this is affected by resistance exercise. Fasted (FAST) muscle protein synthesis was measured in seven healthy young men with a primed constant infusion of L-[ring-(13)C(6)]phenylalanine. Participants then performed an intense bout of unilateral resistance exercise followed by the consumption of 25 g of whey protein to maximally stimulate protein synthesis. In the rested (FED) leg myofibrillar (MYO) protein synthesis was elevated (P < 0.01) above FAST at 3 h (approximately 163%) but not at 1 and 5 h (P > 0.05). In contrast, MYO protein synthesis in the exercised (FED-EX) leg was stimulated above FAST at 1, 3 and 5 h (approximately 100, 216, and 229%, respectively; P < 0.01) with the increase at 5 h being greater than FED (P < 0.01). Thus, the synthesis of muscle contractile proteins is stimulated by both feeding and resistance exercise early (1 h) but has a greater duration and amplitude after resistance exercise. Sarcoplasmic (SARC) protein synthesis was similarly elevated (P < 0.01) above FAST by approximately 104% at 3 h in both FED and FED-EX suggesting SARC protein synthesis is stimulated by feeding but that this response is not augmented by resistance exercise. In conclusion, myofibrillar and sarcoplasmic protein synthesis are similarly, but transiently, stimulated with protein feeding. In contrast, resistance exercise rapidly stimulates and sustains the synthesis of only the myofibrillar protein fraction after protein ingestion. These data highlight the importance of measuring the synthetic response of specific muscle protein fractions when examining the effects of exercise and nutrition.
To draw attention to recent work on the role of protein and the amount of protein needed with each meal to preserve skeletal muscle mass in ageing.
Ageing does not inevitably reduce the anabolic response to a high-quality protein meal. Ingestion of approximately 25-30 g of protein per meal maximally stimulates muscle protein synthesis in both young and older individuals. However, muscle protein synthesis is blunted in elderly when protein and carbohydrate are coingested or when the quantity of protein is less than approximately 20 g per meal. Supplementing regular mixed-nutrient meals with leucine may also enhance the muscle protein synthetic response in elders.
On the basis of recent work, we propose a novel and specific dietary approach to prevent or slow down muscle loss with ageing. Rather than recommending a large, global increase in the recommended dietary allowance (RDA) for protein for all elderly individuals, clinicians should stress the importance of ingesting a sufficient amount of protein with each meal. To maximize muscle protein synthesis while being cognizant of total energy intake, we propose a dietary plan that includes 25-30 g of high quality protein per meal.
The anabolic effect of resistance exercise is enhanced by the provision of dietary protein.
We aimed to determine the ingested protein dose response of muscle (MPS) and albumin protein synthesis (APS) after resistance exercise. In addition, we measured the phosphorylation of candidate signaling proteins thought to regulate acute changes in MPS.
Six healthy young men reported to the laboratory on 5 separate occasions to perform an intense bout of leg-based resistance exercise. After exercise, participants consumed, in a randomized order, drinks containing 0, 5, 10, 20, or 40 g whole egg protein. Protein synthesis and whole-body leucine oxidation were measured over 4 h after exercise by a primed constant infusion of [1-(13)C]leucine.
MPS displayed a dose response to dietary protein ingestion and was maximally stimulated at 20 g. The phosphorylation of ribosomal protein S6 kinase (Thr(389)), ribosomal protein S6 (Ser(240/244)), and the epsilon-subunit of eukaryotic initiation factor 2B (Ser(539)) were unaffected by protein ingestion. APS increased in a dose-dependent manner and also reached a plateau at 20 g ingested protein. Leucine oxidation was significantly increased after 20 and 40 g protein were ingested.
Ingestion of 20 g intact protein is sufficient to maximally stimulate MPS and APS after resistance exercise. Phosphorylation of candidate signaling proteins was not enhanced with any dose of protein ingested, which suggested that the stimulation of MPS after resistance exercise may be related to amino acid availability. Finally, dietary protein consumed after exercise in excess of the rate at which it can be incorporated into tissue protein stimulates irreversible oxidation.
We investigated how myofibrillar protein synthesis (MPS) and muscle anabolic signalling were affected by resistance exercise at 20-90% of 1 repetition maximum (1 RM) in two groups (25 each) of post-absorptive, healthy, young (24 +/- 6 years) and old (70 +/- 5 years) men with identical body mass indices (24 +/- 2 kg m(-2)). We hypothesized that, in response to exercise, anabolic signalling molecule phosphorylation and MPS would be modified in a dose-dependant fashion, but to a lesser extent in older men. Vastus lateralis muscle was sampled before, immediately after, and 1, 2 and 4 h post-exercise. MPS was measured by incorporation of [1,2-(13)C] leucine (gas chromatography-combustion-mass spectrometry using plasma [1,2-(13)C]alpha-ketoisocaparoate as surrogate precursor); the phosphorylation of p70 ribosomal S6 kinase (p70s6K) and eukaryotic initiation factor 4E binding protein 1 (4EBP1) was measured using Western analysis with anti-phosphoantibodies. In each group, there was a sigmoidal dose-response relationship between MPS at 1-2 h post-exercise and exercise intensity, which was blunted (P < 0.05) in the older men. At all intensities, MPS fell in both groups to near-basal values by 2-4 h post-exercise. The phosphorylation of p70s6K and 4EBP1 at 60-90% 1 RM was blunted in older men. At 1 h post-exercise at 60-90% 1 RM, p70s6K phosphorylation predicted the rate of MPS at 1-2 h post-exercise in the young but not in the old. The results suggest that in the post-absorptive state: (i) MPS is dose dependant on intensity rising to a plateau at 60-90% 1 RM; (ii) older men show anabolic resistance of signalling and MPS to resistance exercise.
We tested the hypothesis that increasing blood amino acid (AA) availability would counter the physical inactivity-induced reduction in muscle protein synthesis. We determined how 14 days of unilateral knee immobilization affected quadriceps myofibrillar protein synthesis (MPS) in young healthy subjects (10 men, 2 women, 21 +/- 1 years; 80.2 +/- 4.0 kg, mean +/- S.E.M.) in the post-absorptive state and after infusing AA (10% Primene) at low or high doses (43 and 261 mg kg(-1) h(-1)). Muscle cross-sectional area (MRI) and peak isometric torque declined in the immobilized leg (-5.0 +/- 1.2% and -25 +/- 3%, respectively, both P < 0.005), but were unchanged (all P > 0.6) in the non-immobilized leg. Immobilization induced a 27% decline in the rate of post-absorptive MPS (immobilized, 0.027 +/- 0.003: non-immobilized, 0.037 +/- 0.003% h(-1); P < 0.001). Regardless of dose, AA infusion stimulated a greater rise in MPS in the non-immobilized legs; at 4 h MPS was greater by +54 +/- 12% with low dose and +68 +/- 17% with high dose AA infusion (both P < 0.001). There was some evidence of delayed responsiveness of phosphorylation of Akt to high doses of AA and p70S6k at both doses but no marked differences in that of mTOR, GSK3beta or eEF2. Phosphorylation of focal adhesion kinase (Tyr(576/577)) was reduced (P < 0.05) with immobilization. We observed no change in polyubiquitinated protein content after immobilization. We confirm that 14 days of immobilization reduces MPS in the post-absorptive state and this diminution is reduced but not abolished by increased provision of AA, even at high rates. The immobilization-induced decline in post-absorptive MPS with the 'anabolic resistance' to amino acids can account for much of immobilization-induced muscle atrophy.
The rates of protein synthesis and degradation and of amino acid transport were determined in the leg muscle of untrained postabsorptive normal volunteers at rest and approximately 3 h after a resistance exercise routine. The methodology involved use of stable isotopic tracers of amino acids, arteriovenous catheterization of the femoral vessels, and biopsy of the vastus lateralis muscle. During postexercise recovery, the rate of intramuscular phenylalanine utilization for protein synthesis increased above the basal value by 108 +/- 18%, whereas the rate of release from proteolysis increased by 51 +/- 17%. Muscle protein balance improved (P < 0.05) after exercise but did not become positive (from -15 +/- 12 to -6 +/- 3 nmol phenylalanine.min-1.100 ml leg volume-1). After exercise, rates of inward transport of leucine, lysine, and alanine increased (P < 0.05) above the basal state from 132 +/- 16 to 208 +/- 29, from 122 +/- 8 to 260 +/- 8, and from 384 +/- 71 to 602 +/- 89 nmol.min-1.100 ml leg-1, respectively. Transport of phenylalanine did not change significantly. These results indicate that, during recovery after resistance exercise, muscle protein turnover is increased because of an acceleration of synthesis and degradation. A postexercise acceleration of amino acid transport may contribute to the relatively greater stimulation of protein synthesis.
Six normal untrained men were studied during the intravenous infusion of a balanced amino acid mixture (approximately 0.15 g.kg-1.h-1 for 3 h) at rest and after a leg resistance exercise routine to test the influence of exercise on the regulation of muscle protein kinetics by hyperaminoacidemia. Leg muscle protein kinetics and transport of selected amino acids (alanine, phenylalanine, leucine, and lysine) were isotopically determined using a model based on arteriovenous blood samples and muscle biopsy. The intravenous amino acid infusion resulted in comparable increases in arterial amino acid concentrations at rest and after exercise, whereas leg blood flow was 64 +/- 5% greater after exercise than at rest. During hyperaminoacidemia, the increases in amino acid transport above basal were 30-100% greater after exercise than at rest. Increases in muscle protein synthesis were also greater after exercise than at rest (291 +/- 42% vs. 141 +/- 45%). Muscle protein breakdown was not significantly affected by hyperminoacidemia either at rest or after exercise. We conclude that the stimulatory effect of exogenous amino acids on muscle protein synthesis is enhanced by prior exercise, perhaps in part because of enhanced blood flow. Our results imply that protein intake immediately after exercise may be more anabolic than when ingested at some later time.
Mixed muscle protein fractional synthesis rate (FSR) and fractional breakdown rate (FBR) were examined after an isolated bout of either concentric or eccentric resistance exercise. Subjects were eight untrained volunteers (4 males, 4 females). Mixed muscle protein FSR and FBR were determined using primed constant infusions of [2H5]phenylalanine and 15N-phenylalanine, respectively. Subjects were studied in the fasted state on four occasions: at rest and 3, 24, and 48 h after a resistance exercise bout. Exercise was eight sets of eight concentric or eccentric repetitions at 80% of each subject's concentric 1 repetition maximum. There was no significant difference between contraction types for either FSR, FBR, or net balance (FSR minus FBR). Exercise resulted in significant increases above rest in muscle FSR at all times: 3 h = 112%, 24 h = 65%, 48 h = 34% (P < 0.01). Muscle FBR was also increased by exercise at 3 h (31%; P < 0.05) and 24 h (18%; P < 0.05) postexercise but returned to resting levels by 48 h. Muscle net balance was significantly increased after exercise at all time points [(in %/h) rest = -0.0573 +/- 0.003 (SE), 3 h = -0.0298 +/- 0.003, 24 h = -0.0413 +/- 0.004, and 48 h = -0.0440 +/- 0.005], and was significantly different from zero at all time points (P < 0.05). There was also a significant correlation between FSR and FBR (r = 0.88, P < 0.001). We conclude that exercise resulted in an increase in muscle net protein balance that persisted for up to 48 h after the exercise bout and was unrelated to the type of muscle contraction performed.
We examined the response of net muscle protein synthesis to ingestion of amino acids after a bout of resistance exercise. A primed, constant infusion of L-[ring-2H5]phenylalanine was used to measure net muscle protein balance in three male and three female volunteers on three occasions. Subjects consumed in random order 1 liter of 1) a mixed amino acid (40 g) solution (MAA), 2) an essential amino acid (40 g) solution (EAA), and 3) a placebo solution (PLA). Arterial amino acid concentrations increased approximately 150-640% above baseline during ingestion of MAA and EAA. Net muscle protein balance was significantly increased from negative during PLA ingestion (-50 +/- 23 nmol. min-1. 100 ml leg volume-1) to positive during MAA ingestion (17 +/- 13 nmol. min-1. 100 ml leg volume-1) and EAA (29 +/- 14 nmol. min-1. 100 ml leg volume-1; P < 0.05). Because net balance was similar for MAA and EAA, it does not appear necessary to include nonessential amino acids in a formulation designed to elicit an anabolic response from muscle after exercise. We concluded that ingestion of oral essential amino acids results in a change from net muscle protein degradation to net muscle protein synthesis after heavy resistance exercise in humans similar to that seen when the amino acids were infused.
1. The aim of this study was to describe the time course of the response of human muscle protein synthesis (MPS) to a square wave increase in availability of amino acids (AAs) in plasma. We investigated the responses of quadriceps MPS to a approximately 1.7-fold increase in plasma AA concentrations using an intravenous infusion of 162 mg (kg body weight)(-1) h(-1) of mixed AAs. MPS was estimated from D3-leucine labelling in protein after a primed, constant intravenous infusion of D3-ketoisocaproate, increased appropriately during AA infusion. 2. Muscle was separated into myofibrillar, sarcoplasmic and mitochondrial fractions. MPS, both of mixed muscle and of fractions, was estimated during a basal period (2.5 h) and at 0.5-4 h intervals for 6 h of AA infusion. 3. Rates of mixed MPS were not significantly different from basal (0.076 +/- 0.008 % h(-1)) in the first 0.5 h of AA infusion but then rose rapidly to a peak after 2 h of approximately 2.8 times the basal value. Thereafter, rates declined rapidly to the basal value. All muscle fractions showed a similar pattern. 4. The results suggest that MPS responds rapidly to increased availability of AAs but is then inhibited, despite continued AA availability. These results suggest that the fed state accretion of muscle protein may be limited by a metabolic mechanism whenever the requirement for substrate for protein synthesis is exceeded.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-Delta Delta C(T)) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-Delta Delta C(T)) method. In addition, we present the derivation and applications of two variations of the 2(-Delta Delta C(T)) method that may be useful in the analysis of real-time, quantitative PCR data.
Resistance exercise is a potent stimulator of muscle protein synthesis and muscle cell growth, with the increase in protein synthesis being detected within 2-3 h post-exercise and remaining elevated for up to 48 h. However, during exercise, muscle protein synthesis is inhibited. An increase in AMP-activated protein kinase (AMPK) activity has recently been shown to decrease mammalian target of rapamycin (mTOR) signalling to key regulators of translation initiation. We hypothesized that the cellular mechanism for the inhibition of muscle protein synthesis during an acute bout of resistance exercise in humans would be associated with an activation of AMPK and an inhibition of downstream components of the mTOR pathway (4E-BP1 and S6K1). We studied 11 subjects (seven men, four women) before, during, and for 2 h following a bout of resistance exercise. Muscle biopsy specimens were collected at each time point from the vastus lateralis. We utilized immunoprecipitation and immunoblotting methods to measure muscle AMPKalpha2 activity, and mTOR-associated upstream and downstream signalling proteins, and stable isotope techniques to measure muscle fractional protein synthetic rate (FSR). AMPKalpha2 activity (pmol min(-1) (mg protein)(-1)) at baseline was 1.7 +/- 0.3, increased immediately post-exercise (3.0 +/- 0.6), and remained elevated at 1 h post-exercise (P < 0.05). Muscle FSR decreased during exercise and was significantly increased at 1 and 2 h post-exercise (P < 0.05). Phosphorylation of 4E-BP1 at Thr37/46 was significantly reduced immediately post-exercise (P < 0.05). We conclude that AMPK activation and a reduced phosphorylation of 4E-BP1 may contribute to the inhibition of muscle protein synthesis during resistance exercise. However, by 1-2 h post-exercise, muscle protein synthesis increased in association with an activation of protein kinase B, mTOR, S6K1 and eEF2.