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Enhanced Amino Acid Sensitivity of Myofibrillar Protein Synthesis Persists for up to 24 h after Resistance Exercise in Young Men
Abstract
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.
... On the other hand, several studies [9,10] suggested that MPS can be maintained at a constant level for 24-hours when participants consumed protein or amino acid and exercised. These findings [9,10] indicated that nutrition intake was independent of the time of the day if participants exercised if participants exercised at the same time each day. ...
... On the other hand, several studies [9,10] suggested that MPS can be maintained at a constant level for 24-hours when participants consumed protein or amino acid and exercised. These findings [9,10] indicated that nutrition intake was independent of the time of the day if participants exercised if participants exercised at the same time each day. A recent systematic review was inconclusive regarding the desirable timing of protein intake in healthy adults. ...
Background
In recent years, prevention of sarcopenia and frailty is a matter of concern for community dwelling older persons. The recommended protein daily intake is not fulfilled by 10% of community-dwelling elderly and 35% of residents in aged-care facilities. Furthermore, the optimum time of protein consumption is unclear because of the varying combinations of intake timing and exercise. Although it is desirable to increase protein intake at breakfast and lunch without reducing intake at supper to maximize muscle protein synthesis, this is not clear for older people. Therefore, before considering whether protein consumption at breakfast is superior to other times of the day, its effectiveness needs to be clarified in older adults.
Methods
The inclusion criterion will be healthy or frail adults older than 60 years. This protocol of systematic review adhered to the PRISMA 2020 statement. A comprehensive study strategy is designed for PubMed, EMBASE, CENTRAL, and Clinical Trials.gov. Search strategies will be made using Boolean Search Logic by an experienced librarian in systematic review search formula design. Two authors will carry out independent screening of titles, abstracts, and data extraction for randomized controlled trials. Statistical heterogeneity will be assessed by meta-analysis. Assessment of the risk of bias will be conducted using the Risk-of-bias 2 tool. Integrated data will be analyzed using Review Manager software to create summary tables. Findings summary tables for primary and secondary outcomes will be produced in accordance with the procedures in the Cochrane Handbook.
Results
We believe that the effects of protein or BCAA intake at breakfast in older people analysed in this review will provide evidence that contributes to the establishment of treatment strategies to prevent frailty and sarcopenia.
Conclusion
The benefits of protein intake at breakfast for the elderly will be clarified. This will encourage hospitals and elderly care facilities to review the content of the diet and encourage the elderly to change their own behavior. This is expected to ultimately reduce healthcare costs.
... Resistance exercise (RE) increases the utilization of amino acids from dietary protein for MyoPS in older adults (Pennings et al., 2011;Shad et al., 2016;Yang et al., 2012), a response that may persist for up to 72 h of post-exercise recovery (Burd et al., 2011;McKendry et al., 2019;Miller et al., 2005;Phillips et al., 1997). This is noteworthy as impairments in muscle protein stasis (particularly MyoPS) and the rate of muscle atrophy are most pronounced in the initial days of bed-rest (Di Girolamo et al., 2021;Hardy et al., 2022;Marusic et al., 2021;Tanner et al., 2015). ...
... RE can robustly increase aMyoPS in both the postabsorptive (Biolo et al., 1995;Kumar et al., 2012) and the postprandial state through increasing the utilization of dietary-derived amino acids (Pennings et al., 2011;Yang et al., 2012). RE-induced increases in aMyoPS are reportedly sustained for 24-72 h after exercise (Burd et al., 2011;McKendry et al., 2019;Miller et al., 2005). We and others have previously shown that a single bout of unilateral RE, similar to that used herein, increased iMyoPS rates over 48 h after exercise in older adults (McKendry et al., 2019). ...
Impairments in myofibrillar protein synthesis (MyoPS) during bed rest accelerate skeletal muscle loss in older adults, increasing the risk of adverse secondary health outcomes. We investigated the effect of prior resistance exercise (RE) on MyoPS and muscle morphology during a disuse event in 10 healthy older men (65–80 years). Participants completed a single bout of unilateral leg RE the evening prior to 5 days of in‐patient bed‐rest. Quadriceps cross‐sectional area (CSA) was determined prior to and following bed‐rest. Serial muscle biopsies and dual stable isotope tracers were used to determine rates of integrated MyoPS (iMyoPS) over a 7 day habitual ‘free‐living’ phase and the bed‐rest phase, and rates of acute postabsorptive and postprandial MyoPS (aMyoPS) at the end of bed rest. Quadriceps CSA at 40%, 60% and 80% of muscle length significantly decreased in exercised (EX) and non‐exercised control (CTL) legs with bed‐rest. The decline in quadriceps CSA at 40% and 60% of muscle length was attenuated in EX compared with CTL. During bed‐rest, iMyoPS rates decreased from habitual values in CTL, but not EX, and were significantly different between legs. Postprandial aMyoPS rates increased above postabsorptive values in EX only. The change in iMyoPS over bed‐rest correlated with the change in quadriceps CSA in CTL, but not EX. A single bout of RE attenuated the decline in iMyoPS rates and quadriceps atrophy with 5 days of bed‐rest in older men. Further work is required to understand the functional and clinical implications of prior RE in older patient populations. image
Key points
Age‐related skeletal muscle deterioration, linked to numerous adverse health outcomes, is driven by impairments in muscle protein synthesis that are accelerated during periods of disuse.
Resistance exercise can stimulate muscle protein synthesis over several days of recovery and therefore could counteract impairments in this process that occur in the early phase of disuse.
In the present study, we demonstrate that the decline in myofibrillar protein synthesis and muscle atrophy over 5 days of bed‐rest in older men was attenuated by a single bout of unilateral resistance exercise performed the evening prior to bed‐rest.
These findings suggest that concise resistance exercise intervention holds the potential to support muscle mass retention in older individuals during short‐term disuse, with implications for delaying sarcopenia progression in ageing populations.
... Resistance exercise in the fasted state can stimulate MPS alone 11 however, resistance exercise alongside hyperaminoacidaemia further stimulates MPS 12,13 and post resistance exercise PRO intake represents an important component of maximizing skeletal muscle adaptation to resistance exercise training. 14 The time course of this enhanced exercise-mediated sensitisation of PRO intake on MPS is poorly defined, but it is reported to be evident in trained participants 24 h after a single bout of resistance exercise 15 and up to 48 h 16 and 72 h 17 after resistance exercise in untrained subjects. ...
... 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.
... A single (or 'acute') exercise session directly increases skeletal muscle transport of amino acids 6 and glucose 7 . These effects appear somewhat specific to the contracted musculature, and they enhance postprandial muscle protein synthesis 8 and insulin-stimulated glucose disposal 9,10 in the recovery period after exercise. Consistent exercise training (over weeks, months and years) further augments skeletal muscle mass 11-13 , peripheral insulinsensitivity 12 , maximal oxygen consumption (V . ...
... The stress imposed by a single bout of resistance exercise upregulates amino acid transporters and sensors in muscle at least in part through activating transcription factor 4 (ATF4) 6 . Synergizing with the mammalian target of rapamycin (mTOR) (see the section 'Skeletal muscle responses to acute exercise') ( Fig. 3), this sensitizes muscle to amino acids for ≥24-48 h after resistance exercise 6,8 , and dietary protein intakes of ≥1.2-1.6 g per kg body mass daily modestly complement the hypertrophic response to resistance training 291 . ...
Viewing metabolism through the lens of exercise biology has proven an accessible and practical strategy to gain new insights into local and systemic metabolic regulation. Recent methodological developments have advanced understanding of the central role of skeletal muscle in many exercise-associated health benefits and have uncovered the molecular underpinnings driving adaptive responses to training regimens. In this Review, we provide a contemporary view of the metabolic flexibility and functional plasticity of skeletal muscle in response to exercise. First, we provide background on the macrostructure and ultrastructure of skeletal muscle fibres, highlighting the current understanding of sarcomeric networks and mitochondrial subpopulations. Next, we discuss acute exercise skeletal muscle metabolism and the signalling, transcriptional and epigenetic regulation of adaptations to exercise training. We address knowledge gaps throughout and propose future directions for the field. This Review contextualizes recent research of skeletal muscle exercise metabolism, framing further advances and translation into practice.
... Resistance exercise [1][2][3] and dietary protein ingestion [4][5][6][7] both increase mixed (MPS) and myofibrillar (MyoPS) protein synthesis rates. The additive effect of these two anabolic stimuli repeated over time allows for substantive muscle protein accrual and, therefore, an increase in muscle fiber size [8]. ...
... Dietary protein intake and resistance exercise are the key drivers of skeletal muscle hypertrophy, achieved physiologically by additively stimulating MyoPS rates and thereby facilitating periods of positive net protein balance [1,2,50]. The summative impact of nutrition and resistance exercise has been shown in the hours after a bout of exercise [50], and recent data show that the magnitude of post-exercise daily MyoPS rates are predictive of the level of hypertrophy if training persists (once initial perturbations to novel training stimuli have been accounted for) [8,51,52]. ...
Background:
It remains unclear whether non-animal-derived dietary protein sources (and therefore vegan diets) can support resistance training-induced skeletal muscle remodeling to the same extent as animal-derived protein sources.
Methods:
In Phase 1, 16 healthy young adults (m = 8, f = 8; age: 23 ± 1 y; BMI: 23 ± 1 kg/m2) completed a 3-d dietary intervention (high protein, 1.8 g·kg bm-1·d-1) where protein was derived from omnivorous (OMNI1; n = 8) or exclusively non-animal (VEG1; n = 8) sources, alongside daily unilateral leg resistance exercise. Resting and exercised daily myofibrillar protein synthesis (MyoPS) rates were assessed using deuterium oxide. In Phase 2, 22 healthy young adults (m = 11, f = 11; age: 24 ± 1 y; BMI: 23 ± 0 kg/m2) completed a 10 wk, high-volume (5 d/wk), progressive resistance exercise program while consuming an omnivorous (OMNI2; n = 12) or non-animal-derived (VEG2; n = 10) high-protein diet (∼2 g·kg bm-1·d-1). Muscle fiber cross-sectional area (CSA), whole-body lean mass (via DXA), thigh muscle volume (via MRI), muscle strength, and muscle function were determined pre, after 2 and 5 wk, and postintervention.
Objectives:
To investigate whether a high-protein, mycoprotein-rich, non-animal-derived diet can support resistance training-induced skeletal muscle remodeling to the same extent as an isonitrogenous omnivorous diet.
Results:
Daily MyoPS rates were ∼12% higher in the exercised than in the rested leg (2.46 ± 0.27%·d-1 compared with 2.20 ± 0.33%·d-1 and 2.62 ± 0.56%·d-1 compared with 2.36 ± 0.53%·d-1 in OMNI1 and VEG1, respectively; P < 0.001) and not different between groups (P > 0.05). Resistance training increased lean mass in both groups by a similar magnitude (OMNI2 2.6 ± 1.1 kg, VEG2 3.1 ± 2.5 kg; P > 0.05). Likewise, training comparably increased thigh muscle volume (OMNI2 8.3 ± 3.6%, VEG2 8.3 ± 4.1%; P > 0.05), and muscle fiber CSA (OMNI2 33 ± 24%, VEG2 32 ± 48%; P > 0.05). Both groups increased strength (1 repetition maximum) of multiple muscle groups, to comparable degrees.
Conclusions:
Omnivorous and vegan diets can support comparable rested and exercised daily MyoPS rates in healthy young adults consuming a high-protein diet. This translates to similar skeletal muscle adaptive responses during prolonged high-volume resistance training, irrespective of dietary protein provenance. This trial was registered at clinicaltrials.gov as NCT03572127.
... Altogether, these results indicate a stronger and prolonged anabolic stimulus with RE and feeding combined compared to feeding alone. Furthermore, ingestion of 15 g of whey protein after fatiguing lower body RE increased the rate of MPS (myofibrillar fraction) compared with whey ingestion alone [149]. Song et al. [49] observed increased activation of S6K1 at 1 and 3 h after human participants performed RE with or without feeding, but the magnitude of the elevation was much greater at 1 h when feeding followed RE. ...
... Acute program variables such as volume and intensity of exercise are also important factors in the magnitude of the anabolic response to RE. Performance of 3 sets versus 1 set of lower body resistance exercise elicits a more substantial increase in myofibrillar MPS, increases rpS6 S240/244 phosphorylation 5 h after exercise, and increases the duration of enhanced sensitivity to amino acids (e.g., the following day) [161]. Similarly, 4 sets of unilateral leg extensions performed to failure at 90% and 30% of 1-repetition maximum (1RM) elicited significant increases in myofibrillar MPS and Akt S473 and mTOR S2448 phosphorylation, respectively, one day following RE, whereas performance of a work-matched leg extension protocol using 30% of 1 RM (i.e., not performed to momentary muscle failure) did not result in such increases [149]. Therefore, the load might be of less importance than achieving momentary muscular fatigue with sufficient volume. ...
Skeletal muscle mass is determined by the balance between muscle protein synthesis (MPS) and degradation. Several intracellular signaling pathways control this balance, including mammalian/mechanistic target of rapamycin (mTOR) complex 1 (C1). Activation of this pathway in skeletal muscle is controlled, in part, by nutrition (e.g., amino acids and alcohol) and exercise (e.g., resistance exercise (RE)). Acute and chronic alcohol use can result in myopathy, and evidence points to altered mTORC1 signaling as a contributing factor. Moreover, individuals who regularly perform RE or vigorous aerobic exercise are more likely to use alcohol frequently and in larger quantities. Therefore, alcohol may antagonize beneficial exercise-induced increases in mTORC1 pathway signaling. The purpose of this review is to synthesize up-to-date evidence regarding mTORC1 pathway signaling and the independent and combined effects of acute alcohol and RE on activation of the mTORC1 pathway. Overall, acute alcohol impairs and RE activates mTORC1 pathway signaling; however, effects vary by model, sex, feeding, training status, quantity, etc., such that anabolic stimuli may partially rescue the alcohol-mediated pathway inhibition. Likewise, the impact of alcohol on RE-induced mTORC1 pathway signaling appears dependent on several factors including nutrition and sex, although many questions remain unanswered. Accordingly, we identify gaps in the literature that remain to be elucidated to fully understand the independent and combined impacts of alcohol and RE on mTORC1 pathway signaling.
... Research indicates that MPS is further stimulated, and MPB rates are inhibited when individuals consume a high biological value protein that provides at least ~10 g of essential amino acids (EAAs), particularly leucine, within 2-hour post-exercise (5,8,34,45). Leucine plays a crucial role as a primary EAA in activating the mammalian target of rapamycin complex-1 (mTOR), a key protein responsible for triggering MPS (35). ...
This study examined the effects of resistance training combined with whey protein and leucine blends on muscular strength (1-RM), endurance (repetitions to failure [RTF]), cross-sectional area (CSA), perceived exertion (RPE), and body mass (BM). Thirty-nine men (age = 20.6 ± 1.5 yrs) were randomly assigned to 1 of 3 Groups: (a) 1 dose of 40 g of whey protein and 6.2 g of total leucine (1PRO+L, n = 13); (b) 2 doses of 20 g of whey protein and 6.2 g of total leucine per dose (2PRO+L, n = 12); or (c) placebo (PLA, n = 14). The dependent variables were assessed before and after 8 weeks of high-intensity resistance training 3 d·wk-1. Mixed factorial ANOVAs revealed significant (P < 0.001) increases in BP and LE 1-RM and RTF, VL CSA, a reduction in RPE, and no change in BM (P > 0.05), with no between Group differences. Individual analyses indicated that a greater proportion of the 1PRO+L Group exceeded the minimal important difference for LE 1-RM and RTF compared to those in the 2PRO+L and PLA Groups (P < 0.05). No other differences were observed for the individual responses. These findings indicate that 40 g of whey protein with 6.2 g of total leucine increased LE 1-RM and RTF more than 2 doses of 20 g of whey protein with 6.2 g of total leucine or PLA.
... Exercise stimulates muscle protein synthesis, with significant increases in both myofibrillar (1,2) as well as muscle connective protein synthesis rates (3)(4)(5)(6). The post-exercise increase in myofibrillar and muscle connective protein synthesis rates are responsible for the subsequent skeletal muscle adaptive response to exercise, resulting in the conditioning of the contractile protein and connective tissue networks, respectively (7). ...
Purpose: Ingestion of whey protein increases myofibrillar but not muscle connective protein synthesis rates. Recently, we defined a whey and collagen protein blend (5:1-ratio) to optimize post-prandial plasma amino acid availability. Here, we assessed the ability of this blend to increase myofibrillar and muscle connective protein synthesis rates at rest and during early recovery from exercise.
Methods: In a randomized, double-blind, parallel design, 28 men (age: 25 ± 5 y; BMI: 23.6 ± 2.3 kg/m ² ) were randomly allocated to ingest either 30 g of protein (25 g whey/5 g collagen; BLEND, n = 14) or a non-caloric placebo (PLA, n = 14) following a single session of unilateral leg resistance-type exercise. Participants received primed continuous L-[ ring - ¹³ C 6 ]-phenylalanine infusions with blood and muscle biopsy samples collection for 5 hours post-prandially to assess myofibrillar and muscle connective protein synthesis rates.
Results: Protein ingestion strongly increased plasma amino acid concentrations, including plasma leucine and glycine concentrations ( P < 0.001), with no changes following placebo ingestion ( P > 0.05). Post-prandial myofibrillar and muscle connective protein synthesis rates were higher in the exercised compared to the rested leg ( P < 0.001). In addition, myofibrillar protein synthesis rates were higher in BLEND compared to PLA in both the rested (0.038 ± 0.008 and 0.031 ± 0.006%·h ⁻¹ , respectively; P < 0.05) and exercised (0.052 ± 0.011 and 0.039 ± 0.009%·h ⁻¹ , respectively; P < 0.01) leg. Muscle connective protein synthesis rates were higher in BLEND compared to PLA in the rested (0.062 ± 0.013 and 0.051 ± 0.010%·h ⁻¹ , respectively; P < 0.05), but not the exercised (0.090 ± 0.021 and 0.079 ± 0.016%·h ⁻¹ , respectively; P = 0.11) leg.
Conclusions: Ingestion of a whey (25 g) plus collagen (5 g) protein blend increases both myofibrillar and muscle connective protein synthesis rates at rest and further increases myofibrillar but not muscle connective protein synthesis rates during recovery from exercise in recreationally active, young men.
... In a study, 15 guys checked out muscle growth after resistance training for 24 hours or after protein intake while resting. They did leg exercises at different intensities -30% or 90% of their max strength till failure [70]. As we age, losing muscle mass and strength shoots up the risk of falls and reliance on others. ...
This systematic review examines the synergistic and individual influences of resistance exercise, dietary protein supplementation, and sleep/recovery on muscle protein synthesis (MPS). Electronic databases such as Scopus, Google Scholar, and Web of Science were extensively used. Studies were selected based on relevance to the criteria and were ensured to be directly applicable to the objectives. Research indicates that a protein dose of 20 to 25 grams maximally stimulates MPS post-resistance training. It is observed that physically frail individuals aged 76 to 92 and middle-aged adults aged 62 to 74 have lower mixed muscle protein synthetic rates than individuals aged 20 to 32. High-whey protein and leucine-enriched supplements enhance MPS more efficiently than standard dairy products in older adults engaged in resistance programs. Similarly, protein intake before sleep boosts overnight MPS rates, which helps prevent muscle loss associated with sleep debt, exercise-induced damage, and muscle-wasting conditions like sarcopenia and cachexia. Resistance exercise is a functional intervention to achieve muscular adaptation and improve function. Future research should focus on variables such as fluctuating fitness levels, age groups, genetics, and lifestyle factors to generate more accurate and beneficial results.
... Just 1 session of resistance training can attenuate disuse muscle atrophy during bed rest in older adults [24]. Moreover, A single bout of progressive resistance training can increase the muscle protein anabolic response in older adults [25,26], and muscle protein synthesis has been shown to correlate with increased skeletal muscle thickness [24] and myofiber CSA [27]. Exercise, particularly progressive strength training, appears to mitigate disuse-induced muscle atrophy and may delay the onset or progression of sarcopenia, potentially reducing healthcare costs and enhancing the quality of life for the older population [24]. ...
Background
Hospitalization exacerbates sarcopenia and physical dysfunction in older adults. Whether tailored inpatient exercise prevents acute sarcopenia is unknown. This study aimed to examine the effect of a multicomponent exercise programme on muscle and physical function in hospitalized older adults. We hypothesized that participation in a brief tailored exercise regimen (i.e., 3–5 days) would attenuate muscle function and structure changes compared with usual hospital care alone.
Methods
This randomized clinical trial with blinded outcome assessment was conducted from May 2018 to April 2021 at Hospital Universitario de Navarra, Spain. Participants were 130 patients aged 75 years and older admitted to an acute care geriatric unit. Patients were randomized to a tailored 3‐ to 5‐day exercise programme (n = 64) or usual hospital care (control, n = 66) consisting of physical therapy if needed. The coprimary endpoints were between‐group differences in changes in short physical performance battery (SPPB) score and usual gait velocity from hospital admission to discharge. Secondary endpoints included changes in rectus femoris echo intensity, cross‐sectional area, thickness and subcutaneous and intramuscular fat by ultrasound.
Results
Among 130 randomized patients (mean [SD] age, 87.7 [4.6] years; 57 [44%] women), the exercise group increased their mean SPPB score by 0.98 points (95% CI, 0.28–1.69 points) and gait velocity by 0.09 m/s (95% CI, 0.03–0.15 m/s) more than controls (both p < 0.01). No between‐group differences were observed in any ultrasound muscle outcomes. There were no study‐related adverse events.
Conclusions
Three to 5 days of tailored multicomponent exercise provided functional benefits but did not alter muscle or fat architecture compared with usual hospital care alone among vulnerable older patients. Brief exercise may help prevent acute sarcopenia during hospitalization.
Trial Registration
ClinicalTrials.gov identifier: NCT04600453
... From these data, the muscle protein synthesis rate during the infusion period can be calculated (Figure 1). Over the last 3 decades, the use of primed, continuous, stable isotope-labeled amino acids has advanced our understanding of skeletal muscle protein metabolism, with factors such as physical (in)activity, food ingestion, aging, and disease strongly affecting muscle protein synthesis rates [3][4][5][6][7][8]. ...
... A few groups have examined the mTOR signaling axis (AKT/mTOR/p70S6K1) along with protein synthesis over longer periods (up to 24 h) after RE; however, the results are currently difficult to interpret because the data are sparsely distributed (i.e. large gaps in-between timepoints in the 24 h period) and the exercise intervention varied in loads as well as amino-acid provision [46,59,88,[207][208][209]. Mixed results of later (6< hours) mTOR signaling denotes that mTORC1-dependent signaling may play a more significant role in the early (~1-6 h) rise of protein synthesis following RE, but later time points (~18-36 h) may be regulated by rapamycin-insensitive or mTORC1 independent pathways [56,210]. ...
... Nutritional status is another important component of physical health and is in uenced by PA to some extent. After resistance exercise, enhanced amino acid sensitivity of myo brillar protein synthesis persisted for up to 24 hours [14]. It has been reported that the synergistic effects of nutrition and PA on maintaining skeletal muscle mass and strength are closely related to cognitive function [15]. ...
Background
It has been reported that the cognitive responses to physical activity (PA) in postmenopausal women vary by parity status, and women with higher parity show a significant association between PA and cognitive function. However, the potential pathways mediating the relationship between PA and cognitive function in women with higher parity remain unclear. The objective of this study was to examine this association in Chinese cohort and further investigate the mediating pathways.
Methods
A total of 2296 postmenopausal women were enrolled from the Baoshan District, from April to December 2020. All participant details were collected by interviewer-administered questionnaires, including personal information, medical history, lifestyle body mass index (BMI), cognitive function, nutritional status, and. In this cross-sectional study, generalized linear regression models and the chain-mediation analysis were used to examine the relationship between PA and cognitive function and the mediating pathways.
Results
There was a significant relationship between PA and cognitive function in the high-parity group (≥ three births). In the fully adjusted generalized linear regression model, PA was significantly associated with cognitive function [β: 0.795, 95% confidence interval (CI): 0.251–1.340, P < 0.05]. The chain-mediation analysis showed that depression and nutritional status were two significant mediators, contributing 37.96% of the indirect effect of the overall effect.
Conclusions
Our findings suggest that PA is beneficial for women at a higher risk of cognitive decline, especially those with more than two births, and these benefits are mediated by depression and nutritional status.
... The hours (or days) following a bout of exercise are of particular interest from an MPS perspective due to the synergistic manner by which muscle contraction and dietary protein promote net muscle protein accretion. A bout of exercise independently stimulates MPS, peaking~2 to 6 h postexercize [3,4]) and remaining elevated for~24 to 48 h [5][6][7], though MPB is also stimulated for around 24 h [5,7]. As such, in the postabsorptive state, muscle protein net balance remains negative postexercize [5], but protein (or amino acid) ingestion before [8,9], immediately after [10][11][12][13], or 24 h after [14][15][16], potentiates MPS and, somewhat, inhibits MPB [17] promoting a positive net protein balance. ...
The regulation of postprandial muscle protein synthesis (MPS) with or without physical activity has been an intensely studied area within nutrition and physiology. The leucine content of dietary protein and the subsequent plasma leucinemia it elicits postingestion is often considered the primary drivers of the postprandial MPS response. This concept, generally known as the leucine “trigger” hypothesis, has also been adopted within more applied aspects of nutrition. Our view is that recent evidence is driving a more nuanced picture of the regulation of postprandial MPS by revealing a compelling dissociation between ingested leucine or plasma leucinemia and the magnitude of the postprandial MPS response. Much of this lack of coherence has arisen as experimental progress has demanded relevant studies move beyond reliance on isolated amino acids and proteins to use increasingly complex protein-rich meals, whole foods, and mixed meals. Our overreliance on the centrality of leucine in this field has been reflected in 2 recent systematic reviews. In this perspective, we propose a re-evaluation of the pre-eminent role of these leucine variables in the stimulation of postprandial MPS. We view the development of a more complex intellectual framework now a priority if we are to see continued progress concerning the mechanistic regulation of postprandial muscle protein turnover, but also consequential from an applied perspective when evaluating the value of novel dietary protein sources.
... From a mechanistic perspective, Rasmussen et al. [181] found no differences in phenylalanine rate of disappearance (an indicator of muscle protein synthesis) when essential amino acids (6 g) were consumed 1 hour and 3 hours following an acute bout of resistance training in young, healthy adults (n = 6; 34 yrs.). Burd et al. [182] showed that rates of myofibrillar protein synthesis were still sensitized (responsive) to 15 grams of protein consumed 24-27 hours post-exercise in young, healthy adults (n = 15; 21 yrs.). Thus, even waiting an entire day (post-exercise) to consume a small amount of protein still has muscle anabolic effects. ...
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.
... Esta suplementação, quando alinhada ao período pós-exercício, potencializa o equilíbrio proteico do músculo, contribuindo para adaptações benéficas de longo prazo, incluindo hipertrofia. As taxas de síntese proteica, após essa ingestão, podem permanecer elevadas até 72 horas, coincidindo com a atividade máxima das proteínas que regulam a síntese muscular (Burd et al., 2011). ...
Objetivo: O consumo adequado de proteínas pós-exercício é crucial para a recuperação e o crescimento muscular. A literatura científica debate o momento ideal, quantidade e qualidade das proteínas, exigindo uma compreensão detalhada das fontes e estratégias de consumo. Esta pesquisa visa esclarecer práticas nutricionais para otimizar a performance atlética e a recuperação muscular, fornecendo orientação para atletas e praticantes de atividades físicas. Metodologia: Revisão de literatura utilizando palavras-chave relevantes, como "fonte de proteínas", "recuperação muscular", "exercício físico" e "performance muscular". Resultados: Após exercícios de resistência, a ingestão de proteínas é crucial para a recuperação muscular durante a "janela anabólica", com destaque para fontes ricas em leucina, como soro do leite, carne e ovos. Combinações de proteínas vegetais podem complementar aminoácidos, enquanto a digestibilidade e absorção rápida de proteínas como soro do leite e claras de ovos são vantajosas. Não há correlações diretas entre alto consumo de proteínas e problemas renais ou hepáticos, mas a orientação profissional é vital para otimizar resultados. Conclusão: O consumo de proteínas após o exercício é crucial para a síntese proteica muscular, redução da sua degradação e recuperação mais eficaz no pós-treino. optar por fontes proteicas de alta qualidade e a combinação das diferentes fontes proteicas.
... Subsequently, the magnitude of protein synthesis begins to decrease. 62 Current physical activity guidelines recommend that adults engage in resistance exercises at least twice a week. 1 However, with a longer interval between these bi-weekly sessions, it is hypothesized that more frequent repetitions of resistance exercise could lead to more prolonged periods of net protein accretion in skeletal muscles. 61 Resistance exercise snacks, typically performed once or twice daily, may help maintain this increase in muscle protein. ...
Physical inactivity remains a pressing global public health concern. Prolonged periods of sedentary behavior have been linked to heightened risks of non-communicable diseases such as cardiovascular diseases and type 2 diabetes, while engaging in any form of physical activity can elicit favorable effects on health. Nevertheless, epidemiological research indicates that people often struggle to meet recommended physical activity guidelines, citing time constraints, lack of exercise equipment, and environmental limitations as common barriers. Exercise snacks represents a time-efficient approach with the potential to improve physical activity levels in sedentary populations, cultivate exercise routines, and enhance the perception of the health benefits associated with physical activity. We review the existing literature on exercise snacks, and examine the effects of exercise snacks on physical function and exercise capacity, while also delving into the potential underlying mechanisms. The objective is to establish a solid theoretical foundation for the application of exercise snacks as a viable strategy for promoting physical activity and enhancing overall health, particularly in vulnerable populations who are unable to exercise routinely.
... Recommendations for daily protein intake among athletes are between 1.2 and 2.0 g/kg/day [121,122]; furthermore, the sport intensity, individual regulations, and requirements must also be considered. A higher consumption during intensive training may result in additional benefits [122,123] due to upregulated muscle protein synthesis with an increased sensitivity to protein ingestion during 24 h post-exercise [121,124]. ...
Food and fluid supply is fundamental for optimal athletic performance but can also be a risk factor for caries, dental erosion, and periodontal diseases, which in turn can impair athletic performance. Many studies have reported a high prevalence of oral diseases in elite athletes, notably dental caries 20–84%, dental erosion 42–59%, gingivitis 58–77%, and periodontal disease 15–41%, caused by frequent consumption of sugars/carbohydrates, polyunsaturated fats, or deficient protein intake. There are three possible major reasons for poor oral health in athletes which are addressed in this review: oxidative stress, sports diet, and oral hygiene. This update particularly summarizes potential sports nutritional effects on athletes’ dental health. Overall, sports diet appropriately applied to deliver benefits for performance associated with oral hygiene requirements is necessary to ensure athletes’ health. The overall aim is to help athletes, dentists, and nutritionists understand the tangled connections between sports diet, oral health, and oral healthcare to develop mitigation strategies to reduce the risk of dental diseases due to nutrition.
... Current sport nutrition recommendations advise athletes to ingest 0.3 g/kg body weight of protein post-exercise [30], as the essential amino acids derived from dietary protein are used to stimulate muscle protein synthesis and repair [31]. However, muscle protein synthesis is upregulated for at least 24 hrs following RT [32]; thus, it has been argued that a focus on protein intake in the few hours following training (referred to as the -anabolic window‖) is likely unnecessary if sufficient total daily dietary protein is consumed [33]. Indeed, there is no significant effect of protein timing on muscle hypertrophy where total daily protein intake is controlled for [34]. ...
Purpose
Nutrient timing is a concept that emphasizes the intentional ingestion of whole or fortified foods, and dietary supplements, to adequately fuel for, and recover from, acute and chronic exercise. The nutrition strategies used by powerlifters around training sessions have not been previously investigated. This study explored the self-reported peri-workout (before, during, and after) nutrition practices of competitive powerlifters, including what, why, and information source that informed practice, with comparison to current sport nutrition guidelines.
Methods
Actively competing male (n = 240) and female (n = 65) powerlifters completed a cross-sectional online survey of self-reported peri-workout nutrition practices in the pre-, intra-, and post-exercise periods, fasted training, and supplementation. Data are presented as the number (n) and percentage (%) of all powerlifters practicing a given strategy followed by a % of responses reporting various practices or beliefs within this strategy. Categorical sub-groups (sex, age, and weight class; and competitive caliber) were analyzed with a chi-square test or Fisher's exact test and denoted where significant (p ≤ 0.05).
Results
Most powerlifters reported paying specific attention to nutrition practices in the pre-exercise period (n = 261; 85.6%) by ingesting more carbohydrate (CHO) rich foods (n = 234; 89.6%) for the purpose of assisting in training performance (n = 222; 85.1%). Most powerlifters reported intra-exercise nutrition strategies (n = 211; 69.2%), of which most included ingesting more CHO rich foods (n = 159; 74.5%) for the purpose of feeling less hungry and/or boosting energy levels during training (n = 129; 61.1%). Most powerlifters reported paying attention to post-exercise nutrition (n = 244; 80%), by ingesting more protein rich foods (n = 182; 74.6%) for the purpose of recovering better for the whole day (n = 152; 62.3%) and enhancing the benefits of training (n = 149; 61.1%). Most powerlifters did not complete training sessions in the fasted state (n = 262; 85.9%). Most powerlifters reported paying attention to supplementation before training (n = 237; 77.7%), of which pre-workout formulas (n = 137; 57.8%), energy drinks (n = 101; 42.6%), creatine (n = 88; 37.1%), and caffeine pills (n = 70; 29.5%) were most reported. Supplementation was used to assist in training performance (n = 197; 83.1%) and increase wakefulness/alertness (n = 183; 77.2%). Males reported more often than females that they informed multiple elements of their nutrition practices with the information they read or watched somewhere (p = 0.002 to 0.012).
Conclusion
The peri-workout nutrition practices used by competitive powerlifters followed current sport nutrition guidelines, by using CHO sources to fuel for training and ensuring the provision of protein post-exercise. Competitive powerlifters may wish to exert caution with supplementation, as there is a risk of harm or inadvertent doping.
... The consumption of protein or EAA following resistance exercise further stimulates post-exercise MPS rates as compared with resistance exercise alone, and results in a positive NPB (42,43) . Therefore, acute exercise sensitizes skeletal muscle to the anabolic effects of protein/EAA feeding (43) , an effect that lasts for at least 24 h (44) . In young adults, protein ingestion stimulates MPS rates in a dose-dependent manner up to ∼20 g (containing ∼10 g EAA) following resistance exercise (45,46) . ...
Branched-chain amino acids (BCAA: leucine, isoleucine, and valine) are three of the nine indispensable amino acids, and are frequently consumed as a dietary supplement by athletes and recreationally active individuals alike. The popularity of BCAA supplements is largely predicated on the notion that they can stimulate rates of muscle protein synthesis (MPS) and suppress rates of muscle protein breakdown (MPB), the combination of which promotes a net anabolic response in skeletal muscle. To date, several studies have shown that BCAA (particularly leucine) increase the phosphorylation status of key proteins within the mechanistic target of rapamycin (mTOR) signalling pathway involved in the regulation of translation initiation in human muscle. Early research in humans demonstrated that BCAA provision reduced indices of whole-body and MPB; however, there was no stimulatory effect of BCAA on MPS. In contrast, recent work has demonstrated that BCAA intake can stimulate postprandial MPS rates at rest and can further increase MPS rates during recovery after a bout of resistance exercise. The purpose of this evidence-based narrative review is to critically appraise the available research pertaining to studies examining the effects of BCAA on MPS, MPB, and associated molecular signalling responses in humans. Overall, BCAA can activate molecular pathways that regulate translation initiation, reduce indices of whole-body and MPB, and transiently stimulate MPS rates. However, the stimulatory effect of BCAA on MPS rates is less than the response observed following ingestion of a complete protein source providing the full complement of indispensable amino acids.
... Following a single bout of resistance exercise the muscle is sensitized to anabolic stimuli for up to 72 hours 43 . This anabolic window potentially shortens with repeated training 44 , but it is still thought to last a considerable amount of time (~24 hours) 45 . When food is consumed in this post-exercise window, the protein synthetic response is augmented above levels in the absence of that resistance training bout and protein breakdown is suppressed 46 . ...
In this chapter we present an overview of periodisation introduceing and discussing its definition and historical development. We then consider the common argument that strength and hypertrophic adaptations are optimised through the application of periodisation, and provide alternative interpretations that we think likely reflect more parsimonious explanations than appeals to periodisation ‘theory’. Lastly, we will consider its structure as a myth vs as a scientific theory in the Popperian sense. From our perspective and analysis, it does not feel unfair to label periodisation as a myth. At the very least it has strong elements of mythos about it particularly in terms of its origin and development. If periodisation is to take a step forward into the beginnings of a scientific theory, then consensus specification and definition such that it yields clear deductively testable consequences should be the next point in its journey from mythical origins.
... The addition of carbohydrate provision offers no further anabolic effects post-exercise [116], highlighting the central role of EAA in maximising anabolic responses in protein turnover to exercise. In some cases, the enhanced MPS response due to protein  exercise interactions can last up to 24 h [117] and even 48 h [41] following exercise, although the magnitude of this response falls over time. With this in mind (i.e., the delay of muscle full lasting up to 24e48 h), the timing of protein intake pre-, during-or post-exercise may not be as crucial for muscle anabolism as first thought; rather the quantity/quality of the protein may be the most fundamental consideration [6]. ...
Muscle protein synthesis (MPS) and muscle protein breakdown (MPB) are influenced through dietary protein intake and physical (in)activity, which it follows, regulate skeletal muscle (SKM) mass across the lifespan. Following consumption of dietary protein, the bio-availability of essential amino acids (EAA), and primarily leucine (LEU), drive a transient increase in MPS with an ensuing refractory period before the next MPS stimulation is possible (due to the "muscle full" state). At the same time, MPB is periodically constrained via reflex insulin actions. Layering exercise on top of protein intake increases the sensitivity of SKM to EAA, therefore extending the muscle full set-point (∼48 h), to permit long-term remodelling (e.g., hypertrophy). In contrast, ageing and physical inactivity are associated with a premature muscle full set-point in response to dietary protein/EAA and contractile activity. Of all the EAA, LEU is the most potent stimulator of the mechanistic target of rapamycin complex 1 (mTORC1)-signalling pathway, with the phosphorylation of mTORC1 substrates increasing ∼3-fold more than with all other EAA. Furthermore, maximal MPS stimulation is also achieved following low doses of LEU-enriched protein/EAA, negating the need for larger protein doses. As a result, LEU supplementation has been of long term interest to maximise muscle anabolism and subsequent net protein accretion, especially when in tandem with resistance exercise. This review highlights current knowledge vis-à-vis the anabolic effects of LEU supplementation in isolation, and in enriched protein/EAA sources (i.e., EAA and/or protein sources with added LEU), in the context of ageing, exercise and unloading states.
... The range of protein requirement in both resistance training [28,30] and endurance athletes [18,31] may be attributed to the measurement conditions related to physical activity, such as no exercise for 48 h [30], after 8 h of exercise [18,28], and after 24 h of exercise [31]. These results have been obtained only in resistance-trained athletes; nonetheless, a single exercise session increases muscle protein synthesis 24 to 48 h later, thereby increasing sensitivity to dietary protein intake [50][51][52]. Therefore, the protein requirements for athletes and persons with high physical activity should be set using the IAAO method after considering various situations including physical activity level, during exercise, and elapsed time after exercising. ...
Background:
The indicator amino acid oxidation (IAAO) method has been accepted as an approach to evaluate habitual protein requirements under free-living conditions.
Objective:
This scoping review reports on literature that evaluated protein requirements in humans using the IAAO methods.
Methods:
Three databases (PubMed/Medline, Web of Science, and ProQuest) were systematically searched to identify studies that evaluated protein requirements using the IAAO method published in English until June 5, 2023. We evaluated the study quality using previously developed criteria. We extracted the characteristics of the study design and the results of protein requirements. Two reviewers conducted both reviews and quality assessments independently; any differences among them were resolved by consensus or agreement of all team members.
Results:
We extracted 16 articles targeting children, young adults (including pregnant women, resistance training athletes, endurance training athletes, and team sports), and older adults. For quality assessment, 14 studies were evaluated "strong", but the remaining two were "moderate". These studies were conducted in only three countries and not for all sexes or life stages. The range of the estimated average protein requirements of each life stage were 1.3 g/kg body weight/day for children, 0.87 to 2.1 (0.87 - 0.93 for general young adults, 1.22 - 1.52 for pregnant women, 1.49 - 2.0 for resistance-trained athletes, 1.65 - 2.1 for endurance athletes and 1.2 - 1.41 for team sports athletes) g/kg body weight/day for young adults, and 0.85 to 0.96 g/kg body weight/day for older adults.
Conclusions:
Protein requirements in 14 studies were higher than the current reference for each sex, life stage and physical activity that are related to protein requirement. In the future, protein requirements of various population including sex, life stage could be assessed using the IAAO methods worldwide.
... Traininginduced increases in muscle mass are mechanistically underpinned by persistent periods of positive net protein balance, and therefore protein accretion, within muscle tissue (Fujita et al., 2007). A single bout of resistance exercise stimulates muscle protein synthesis (MPS) rates, peaking in the immediate hours subsequent (~2-6 h; van Vliet et al., 2019) and remaining elevated for ~24-48 h (Biolo et al., 1995;Burd et al., 2011;Phillips et al., 1997). However, resistance exercise also stimulates muscle protein breakdown (MPB) rates such that, in the postabsorptive state, muscle protein net balance remains negative (Biolo et al., 1995). ...
Background
Dietary protein ingestion augments post (resistance) exercise muscle protein synthesis (MPS) rates. It is thought that the dose of leucine ingested within the protein (leucine threshold hypothesis) and the subsequent plasma leucine variables (leucine trigger hypothesis; peak magnitude, rate of rise, and total availability) determine the magnitude of the postprandial postexercise MPS response.
Methods
A quantitative systematic review was performed extracting data from studies that recruited healthy adults, applied a bout of resistance exercise, ingested a bolus of protein within an hour of exercise, and measured plasma leucine concentrations and MPS rates (delta change from basal).
Results
Ingested leucine dose was associated with the magnitude of the MPS response in older, but not younger, adults over acute (0–2 h, r ² = 0.64, p = 0.02) and the entire postprandial (>2 h, r ² = 0.18, p = 0.01) period. However, no single plasma leucine variable possessed substantial predictive capacity over the magnitude of MPS rates in younger or older adults.
Conclusion
Our data provide support that leucine dose provides predictive capacity over postprandial postexercise MPS responses in older adults. However, no threshold in older adults and no plasma leucine variable was correlated with the magnitude of the postexercise anabolic response.
... Das im Getränk enthaltene Protein wird im Verdauungstrakt in die einzelnen Aminosäuren aufgespalten; diese gelangen ebenfalls in den Blutkreislauf, wo sie zur Resynthese von Strukturproteinen im Körper und zum Reparieren beschädigter Gewebe verwendet werden können. Die Proteinsynthese ist 24 Stunden nach dem Training hochreguliert, was zu erhöhter Empfindlichkeit gegenüber oraler Proteinzufuhr während dieser Zeit führt [5,9]. Diese erhöhte Absorption bietet einen idealen Zeitpunkt für die Optimierung der Proteinzufuhr, um Regenerations-und Anpassungsprozesse nach einer Belastung zu optimieren, da eine längere Belastung zu einem katabolen Zustand und zu einem daraus resultierenden Muskelabbau führen kann. ...
... However, while informative for our RCT, we also recognize that our findings may not necessarily reflect the postprandial BCAA excursions that could have occurred if our study was conducted with resistance exercise. The anabolic effect of resistance exercise is strong and may persist for up to 48 h (Burd et al. 2011), and this may cause postprandial leucine/BCAA plasma concentrations to be dampened postexercise due to a concomitant increased muscle uptake of AAs for protein synthesis (Mero et al. 2009). Important future work would be to assess GY versus MILK (and/or other higher protein wholefoods) acutely with exercise and chronically in a training study with protein-matched diets, and to assess whether these foods differentially stimulate MPS acutely, as was suggested by Jakobsson (2019) in a recently published commentary on our RCT. ...
We examined postprandial branched-chain amino acid (BCAA), insulin, and glucose responses in blood for 4 h following the consumption of two isonitrogenous doses (2 × 20 g protein) of Greek-style yogurt (GY) and skimmed milk (MILK) in young males. Peak leucine and BCAA concentrations and areas under the curve were greater after GY versus MILK, and time to maximal leucine/BCAA concentrations was similar between conditions. We demonstrated that different protein-matched wholefood dairy products elicit different postprandial aminoacidemic responses.
... Dabei wird die positive Nettobilanz weniger durch eine Suppression der MGP als vielmehr eine Erhöhung der grundsätzlich wesentlich dynamischeren MPS als Reaktion auf das Krafttraining generiert(Glynn et al. 2010). Krafttraining und Proteingabe haben einen synergistischen Effekt auf die MPS, vereinfacht dargestellt erhöht Krafttraining also die Sensitivität des Skelettmuskels für AS, ein Effekt der 24-48 h anhält(Burd et al. 2011).Ungleich zum Krafttraining, bei dem die muskuläre Hypertrophie die vorherrschende Anpassung darstellt, stehen beim Ausdauertraining Veränderungen des Substratmetabolismus, mitochondriale Biogenese und Angiogenese als Anpassungserscheinungen im Vordergrund. Vergleichbar dem Krafttraining bleibt die MPS bis zu 24 h "post-exercise" signifikant erhöht. ...
Die Trainingswissenschaft greift auf mehr oder weniger elaborierte Heuristiken, Theorien, Konzepte und Modelle zur Beschreibung, Erklärung und Ergründung von Anpassungs-, Regelungs- und Steuerungsprozessen zurück. Die Erklärungskraft der jeweiligen Theorien und Modelle zu Anpassungsprozessen durch Training sowie zur Trainingssteuerung reichen dabei von einer veranschaulichenden (didaktischen) Betrachtung bis hin zu empirisch prüfbaren Modellvorstellungen mit strukturerklärendem Inhalt. Integrative Theorien und Modelle zum Training stehen jedoch vor der schwierigen bis nicht lösbaren Aufgabe, dass sie einerseits heterogene, morphologische, funktionelle Adaptationen auf unterschiedlichen Funktionsebenen erklären und andererseits Leistungsentwicklungen im koordinativen, technisch-taktischen Bereich aufgrund von informationsprozess-gestützten, handlungsregulativen Anpassungen abbilden sollen. Dieser Beitrag ist Teil der Sektion Sportmotorische Fähigkeiten und sportliches Training, herausgegeben vom Teilherausgeber Michael Fröhlich, innerhalb des Handbuchs Sport und Sportwissenschaft, herausgegeben von Arne Güllich und Michael Krüger.
... g/kg BW (corresponding to~2-3 g leucine) that results in maximum postprandial MPS in young adults. Similar findings have been reported in studies evaluating postprandial MPS responses to dietary protein following resistance training bouts, though MPS rates are further augmented as exercise enhances the sensitivity of muscle to the anabolic properties of protein [13,16,40]. Factoring in possible interindividual variability and acknowledging "real world" mixed-macronutrient meals that likely include lower quality protein sources and food matrices that modify protein digestion, absorption, and aminoacidemia, subsequent publications have advised intakes of~0.4-0.5 g protein/kg BW/meal for athletes [15,41,42], including soccer players [3]. ...
Dietary protein is required to support recovery and adaptation following exercise training. While prior research demonstrates that many athletes meet total daily protein needs, intake seems to be predominantly skewed toward the evening meal. An even distribution of protein doses of ≥0.24 g/kg BW consumed throughout the course of a day is theorized to confer greater skeletal muscle anabolism outcomes compared to a skewed pattern of intake. Protein quality is also an important dietary consideration for athletes, with the amino acid leucine seemingly serving as the primary driver of the postprandial anabolic response. The present study investigates protein consumption characteristics among a cohort of NCAA D1 soccer players and evaluates differences between male and female athletes. Athletes were instructed to complete 3-day food diaries, which were subsequently analyzed and compared to UEFA expert group-issued nutrition guidelines for soccer players. Breakfast, lunch, and dinner accounted for 81.4% of the total daily dietary protein intake. Most athletes (77.8%) ingested optimum amounts of protein at dinner but not at breakfast (11.1%) or lunch (47.2%). In addition, statistically significant sex-based differences in daily dietary protein intake, meal-specific protein amounts, and protein quality measures were detected. Findings indicate suboptimal dietary protein intake practices among the collegiate soccer athletes.
... 33 Direnç egzersizleriyle kasların diyetteki proteine 24 saat kadar duyarlı kaldığı gösterilmiş ve bu süre gelişmiş kas remodelasyonu ve adaptasyonu için "fırsat penceresi" olarak nitelendirilmiştir. 34 Ancak araştırmalar bu sürenin sporcuların antrenman düzeyine göre değiştiğini ve protein alımı zamanlamasının çok önemli olduğunu ortaya koymuştur. 35 Bu nedenle hem endurans hem de direnç egzersizleri sonrası ilk 3-4 saatte protein desteğinin sağlanması gerektiği ifade edilmektedir. ...
30 porcular temel performans parametrelerini geliştirmeye yönelik egzersizlere antrenman programlarında yer verirler. Optimal performans düzeyi için en önemli belirleyici antrenman olmakla birlikte beslenme de çok önemli ve etkili bir komponentdir. Doğru bir beslenme planı sporcuların optimal performansın gerek-tirdiği enerji düzeyine sahip olmalarını, ideal kilolarında kalmalarını ve antrenmanın programının bütün aşamalarında kendilerini iyi hissetmelerini sağlayacaktır. İdeal bir beslenme planı oluşturmak deneyimli sporcular için bile kolay bir durum değildir. 1 Sporcu Beslenmesi ve Antrenman İlişkisi Nasıl Sağlanmalı? Ö ÖZ ZE ET T Sporda başarıyı sağlayan pek çok faktör olmakla birlikte beslenme anahtar bir rol üstlen-mektedir. Araştırma sonuçları planlı ve bilimsel bir beslenme stratejisinin sportif performansı ge-liştirdiği yönünde sonuçlar vermektedir. Sporcuya özel ve antrenman periyodizasyonuna uygun bireysel beslenme stratejisinin spor türü, performans beklentisi, hedefleri, sporcunun beslenme alış-kanlıkları ve tercihlerinin dikkate alınarak oluşturulması gerekmektedir. Sporcularda egzersiz ön-cesi optimal beslenmenin sağlanması ve egzersiz sonrası toparlanmanın desteklenmesi için yeterli düzeyde günlük enerji alımı şarttır. Total enerji ihtiyacının sağlanması kaydıyla sporcunun tercih-lerine ve toleransına göre düzenleme yapılabilir. Dengeli bir beslenme fiziksel aktivite nedeniyle artan enerji ihtiyacını karşılayabilmelidir. İyi bir beslenme, yoğun antrenman programını destek-lediği gibi kassal toparlanma ve endürans egzersizlerine olan metabolik adaptasyonu kolaylaştırır. Bu derlemede, sporcu beslenmesi ve antrenman ilişkisinin öneminden bahsedilecek ve beslenme yaklaşımları ile fizyolojik yanıtlar hakkında pratik önerilere yer verilecektir. A An na ah ht ta ar r K Ke el li im me el le er r: : Sporcular; egzersiz; beslenme durumu; spor performansı A AB BS ST TR RA AC CT T A number of factors contribute to success in sport, and diet is a key component. Research findings show that a planned scientific nutritional strategy is related to better sports performance. Individualized and periodized nutritional strategy according to training program should depend on several aspects, including the sport, the athlete's goals, the environment, and practical issues. Daily energy intake is essential in athletes, and should be timed according to training sessions in order to ensure optimal pre-workout nutrition, as well as to encourage recovery post workout. If this is not possible during the day, the intake should be tailored according to individual preference and tolerance, provided that the total daily requirements are met. Maintenance of the energy balance in individuals with increased requirements because of physical activity is important. Good nutrition assists in the ability to train intensely, as well as in muscle recovery and metabolic adaptations to endurance exercise. This review will focus on the importance of the interaction between sports nutrition and training status, and discuss practical recommendations about nutritional approaches and physiological responses. K Ke ey y W Wo or rd ds s: : Athletes; exercise; nutritional status; sports performance T Tu ur rk ki iy ye e K Kl li in ni ik kl le er ri i J J S Sp po or rt ts s M Me ed d-S Sp pe ec ci ia al l T To op pi ic cs s 2 20 01 16 6; ;2 2((3 3)):
... Required sample size was calculated with differences in postprandial muscle FSR as the primary outcome measure. On the basis of the studies comparing postprandial muscle FSR at rest and after exercise in young [25] and older [26] populations, we calculated the sample size needed to show a difference in postprandial muscle protein synthesis rates between the rested and exercised leg. Using a power of 80%, a significance level of 0.05, and including potential dropouts, the final number of participants needed was calculated to be n ¼ 14 in the young group and n ¼ 15 in the older group. ...
Background:
Ingestion of protein concentrates or isolates increases muscle protein synthesis rates in young and older adults. There is far less information available on the anabolic response following the ingestion of dairy wholefoods, which are commonly consumed in a normal diet.
Objectives:
This study investigates whether ingestion of 30 g protein provided as quark increases muscle protein synthesis rates at rest and whether muscle protein synthesis rates are further increased after resistance exercise in young and older adult males.
Methods:
In this parallel-group intervention trial, 14 young (18-35 y) and 15 older (65-85 y) adult males ingested 30 g protein provided as quark after a single-legged bout of resistance exercise on leg press and leg extension machines. Primed, continuous intravenous L-[ring-13C6]-phenylalanine infusions were combined with the collection of blood and muscle tissue samples to assess postabsorptive and 4-h postprandial muscle protein synthesis rates at rest and during recovery from exercise. Data represent means ± SDs; η2 was used to measure the effect size.
Results:
Plasma total amino acid and leucine concentrations increased after quark ingestion in both groups (both time: P < 0.001; η2 > 0.8), with no differences between groups (time × group: P = 0.127 and P = 0.172, respectively; η2<0.1). Muscle protein synthesis rates increased following quark ingestion at rest in both young (from 0.030 ± 0.011 to 0.051 ± 0.011 %·h-1) and older adult males (from 0.036 ± 0.011 to 0.062 ± 0.013 %·h-1), with a further increase in the exercised leg (to 0.071 ± 0.023 %·h-1 and to 0.078 ± 0.019 %·h-1, respectively; condition: P < 0.001; η2 = 0.716), with no differences between groups (condition × group: P = 0.747; η2 = 0.011).
Conclusions:
Quark ingestion increases muscle protein synthesis rates at rest with a further increase following exercise in both young and older adult males. The postprandial muscle protein synthetic response following quark ingestion does not differ between healthy young and older adult males when an ample amount of protein is ingested. This trial was registered at the Dutch Trial register, which is accessible via trialsearch.who.int www.trialregister.nl as NL8403.
... During resistance training, frequency significantly affects the muscle strength, with a higher training frequency producing more strength and muscle mass [42][43][44]. Studies have shown that exercise-induced increases in muscle protein synthesis last approximately 24-48 h [45,46]. In addition, a higher training frequency can evenly distribute training volume throughout the week, reducing fatigue [47]. ...
We studied the effect of blood flow restriction (BFR) combined with low-intensity resistance training (LIRT) on lower-limb muscle strength and mass in post-middle-aged adults. The PubMed, OVID, ProQuest, Cochrane Library, EMBASE, Web of Science, and Scopus databases were used to obtain randomized controlled trials, and the effects of BFR and LIRT (BFRt) on muscle strength and mass in adults were examined. The Cochrane risk of bias tool assessed bias in the included trials. The combined effects of BFR and LIRT (BFRt) were calculated by meta-analysis, the association between muscle strength/mass and interventions was determined by meta-regression, and beneficial variables of intervention were explored by subgroup analysis. A total of 11 articles were included in the meta-analysis. The combined effects showed that BFRt significantly improved lower extremity muscle strength but not muscle mass gain. Meta-regression analysis indicated that the effect of BFRt on changes in muscle strength was correlated with frequency of the intervention. Subgroup analysis revealed that BFRt achieved greater muscle strength gains than normal activity, LIRT, and similar muscle strength gains compared to high-intensity resistance training. The increased muscle strength after BFRt was noticed with a frequency of three times a week, but not with a frequency of two times a week, and the difference between these subgroups was statistically significant. Our findings indicate that BFRt can increase lower-limb muscle strength in post-middle-aged adults. Frequency of intervention is a key variable; particularly, a schedule of three times a week is effective in improving muscle strength.
... Furthermore, compared to the usual gait speed, a marker of daily activity with lower frequency and intensity of exercise, fast walking speed is a better predictor of functional decline [42] because it is highly dependent on muscle strength and lower extremity functioning. A combination of walking for exercise more frequently and amino acid intake could improve the absorption response and musculoskeletal sensitivity to amino acids, thus enhancing muscle protein synthesis [43]. ...
Citation: Liao, M.; Mu, Y.; Su, X.; Zheng, L.; Zhang, S.; Chen, H.; Xu, S.; Ma, J.; Ouyang, R.; Li, W.; et al. Association between Branched-Chain Amino Acid Intake and Physical Function among Chinese Community-Dwelling Elderly Residents. Nutrients 2022, 14, 4367. https://doi.
Background
It has been reported that the cognitive responses to physical activity (PA) in postmenopausal women vary by parity status, and women with higher parity show a significant association between PA and cognitive function. However, the potential pathways mediating the relationship between PA and cognitive function in women with higher parity remain unclear. The objective of this study was to examine this association in Chinese cohort and further investigate the mediating pathways.
Methods
A total of 2296 postmenopausal women were enrolled from the Baoshan District, from April to December 2020. All participant information was collected through interviewer-administered questionnaires or measurements, including personal information, medical history, lifestyle, body mass index (BMI), cognitive function, nutritional status, and depression status. In this cross-sectional study, generalized linear regression models and the chain-mediation analysis were used to examine the relationship between PA and cognitive function and the mediating pathways.
Results
There was a significant relationship between PA and cognitive function in the high-parity group (≥ three births). In the fully adjusted generalized linear regression model, PA was significantly associated with cognitive function [β: 0.795, 95% confidence interval (CI): 0.251–1.340, P < 0.05]. The chain-mediation analysis showed that depression and nutritional status were two significant mediators, contributing 37.96% of the indirect effect of the overall effect.
Conclusions
Our findings suggest that PA is beneficial for women (≥ three births) to maintain cognitive function, and these benefits are mediated by depression and nutritional status.
Karma öğretim yöntemi ile beden eğitimi ve spor ilişkisi
A Síndrome do Envelhecimento Precoce Bucal (SEPB) é uma condição multifatorial em ascensão entre os jovens, marcada por um envelhecimento precoce das estruturas orais, como dentes, periodonto, polpa dentária, osso, ATM e músculos, apresentando sintomas clínicos que não correspondem à idade fisiológica do indivíduo. Este trabalho tem por objetivo realizar uma revisão de literatura qualitativa para identificar e avaliar os principais fatores de risco associados ao desenvolvimento de erosão dentária em atletas. Trata-se de uma revisão bibliográfica integrativa com abordagem qualitativa. Os artigos foram selecionados nas bases de dados LILACS, SCIELO, PUBMED, utilizando os descritores: Envelhecimento precoce, Odontologia do Esporte, Erosão dentária, Lesões Cervicais Não Cariosas. A literatura aponta que os atletas são mais vulneráveis à erosão dentária devido à alta incidência de fatores de risco que estão expostos. O exercício físico intenso e contínuo pode causar refluxo gástrico ou necessitar de suplementação energética, além de dietas específicas e ingestão de bebidas e gel isotônicos. É evidente que estratégias preventivas eficazes devem incluir a educação dos atletas sobre os riscos associados ao consumo de bebidas ácidas e suplementos, assim como a implementação de práticas adequadas de higiene bucal e monitoramento regular da saúde dental.
The intensive care unit (ICU) environment is one of the most challenging for skeletal muscle health. The atrophy associated with clinical care is distinct from that seen with inactivity or immobilization in the absence of disease and is exacerbated by aging. The substantial muscle loss in the ICU is likely due to the presence of inflammation, elevated proteolysis, bedrest, and undernutrition. Skeletal muscle parameters (e.g., mass, composition/quality) at admission are predictive of mortality and other clinically important outcomes. Treatment goals to mitigate muscle loss should be early mobilization and adequate nutrient supply, especially protein, using an individualized approach to support the maintenance and recovery of skeletal muscle.
Research on lean, energy-deficient athletic and military cohorts has broadened the concept of the Female Athlete Triad into the Relative Energy Deficiency in Sport (REDs) syndrome. REDs represents a spectrum of abnormalities induced by low energy availability (LEA), which serves as the underlying cause of all symptoms described within the REDs concept, affecting exercising populations of either biological sex. Both short- and long-term LEA, in conjunction with other moderating factors, may produce a multitude of maladaptive changes that impair various physiological systems and adversely affect health, well-being, and sport performance. Consequently, the comprehensive definition of REDs encompasses a broad spectrum of physiological sequelae and adverse clinical outcomes related to LEA, such as neuroendocrine, bone, immune, and hematological effects, ultimately resulting in compromised health and performance.
In this review, we discuss the pathophysiology of REDs and associated disorders. We briefly examine current treatment recommendations for REDs, primarily focusing on non-pharmacological, behavioral, and lifestyle modifications that target its underlying cause – energy deficit. We also discuss treatment approaches aimed at managing symptoms, such as menstrual dysfunction and bone stress injuries, and explore potential novel treatments that target the underlying physiology, emphasizing the roles of leptin and the activin-follistatin-inhibin axis, the roles of which remain to be fully elucidated, in the pathophysiology and management of REDs.
In the near future, novel therapies leveraging our emerging understanding of molecules and physiological axes underlying energy availability or lack thereof may restore LEA-related abnormalities, thus preventing and/or treating REDs-related health complications, such as stress fractures, and improving performance.
Background
Although resistance training (RT) is essential to preserve musculoskeletal fitness and maintain a healthy, independent life into old age, few women perform RT. We investigated whether resistance exercise snacking (RES) could be an efficient training approach for the workplace health promotion (WHP) to minimize barriers for participation and facilitate RT in women in order to improve musculoskeletal fitness.
Methods
This pilot-study followed a prospective, controlled intervention design. Female employees with sedentary occupations doing RT on less than 2 days/week before study participation were included. Participants self-selected for either intervention (IG) or control group (CG). While the IG [N = 15, mean age 42.1 (SD = 11.1) years] did 10 min of RES on working days for 12 weeks, the CG [N = 15, mean age 49.9 (SD = 9.7) years] was instructed to maintain their habitual physical activity. Primary endpoint was change in muscle mass. Secondary endpoint was change in maximum isometric strength. Balance, cardiovascular fitness, perceived health, and general life satisfaction was assessed for exploratory purpose. Measurements were taken before and after the intervention.
Results
12 participants of IG and 14 of CG completed the study. Muscle mass improved significantly more in the IG [+0.42 (SD = 0.54) kg] compared to the CG [−0.16 (SD = 0.51) kg] (p = 0.01, ƞ²p = 0.24). Strength did not change significantly between groups. Nevertheless, there was a trend for greater improvements in the IG compared to the CG for trunk extension, trunk flexion, and upper body push but not upper body pull. Regarding exploratory endpoints, no significant between-group changes were found. Despite their poor fitness, both groups perceived their health as good and had high life satisfaction before and after the intervention.
Conclusion
RES could be an effective approach for the WHP to promote RT in inactive women with sedentary occupations and improve their muscle mass.
We have seen that a single resistance exercise session without additional intake of dietary protein is able to increase MPS for a few hours to more than 72 h, depending on the stimulus, but NBIL remains negative after resistance exercise because MPB also increases with resistance exercise. The increase in MPS, measured after a single resistance exercise session and averaged, is greater in young men compared to seniors. Further, you have learned that there is a dose-response relationship between the FF recruitment time integral, denominated «effective time under tension» (ETUT) to exhaustion (i.e., to significant force decay) and the increase in (myofibrillar) MPS after resistance exercise, and that recruitment of FF motor units can be accomplished by multiple strategies.
Simple Summary
Exercise has well-known health benefits, but the way our muscles use carbohydrates and lipids as fuel during exercise is complex. It is not just about the physical activity itself; it also depends on our body’s metabolic state. The balance between using carbs and fats affects exercise performance. This review aims to provide a comprehensive look at how our bodies choose fuel sources during exercise by summarizing existing research. Understanding this can lead to advancements in exercise science and personalized exercise strategies for better health and performance.
Abstract
Exercise is widely recognized for its positive impact on human health and well-being. The process of utilizing substrates in skeletal muscle during exercise is intricate and governed by complex mechanisms. Carbohydrates and lipids serve as the primary fuel sources for skeletal muscle during exercise. It is now understood that fuel selection during exercise is not solely determined by physical activity itself but is also influenced by the overall metabolic state of the body. The balance between lipid and carbohydrate utilization significantly affects exercise capacity, including endurance, fatigue, and overall performance. Therefore, comprehensively understanding the regulation of substrate utilization during exercise is of utmost importance. The aim of this review is to provide an extensive overview of the current knowledge regarding the pathways involved in the regulation of substrate utilization during exercise. By synthesizing existing research, we can gain a holistic perspective on the intricate relationship between exercise, metabolism, and fuel selection. This advanced understanding has the potential to drive advancements in the field of exercise science and contribute to the development of personalized exercise strategies for individuals looking to optimize their performance and overall health.
Use of leucine-enriched amino acids was started in sports nutrition, and their effectiveness in obtaining functional improvements for individuals with sarcopenia has become widely recognized in recent years. Sarcopenia can also arise in stroke patients, and countermeasures against sarcopenia should not be considered as a separate issue for stroke patients, but should instead be considered inherent. As a prerequisite for smooth improvement of physical function in stroke, the first requirement is sufficient energy. The next step is leucine-enriched amino acids. When using amino acids, administration in combination with exercise therapy rather than in isolation is important, but the timing of intake is also attracting attention. This chapter details the expected effects of and conditions for using leucine-enriched amino acids in stroke patients.
Nutrition for endurance athletes has been a hotly debated topic among athletes, coaches, trainers, and others in the fitness industry. Healthcare professionals who treat athletes also need to be aware of what foods athletes are eating and supplements athletes are taking and should be up to date on current evidence regarding sports nutrition recommendations. While some research is conflicting and nutrition recommendations have been argued, the field has evolved over the years with more concrete evidence better defining parameters for macronutrients, micronutrients, hydration, and ergogenic aids. Providers should liaise with sports dietitians whenever possible to keep up to date on this ever-changing field. This chapter reviews current nutrition recommendations for endurance athletes to help clinicians and providers educate and counsel athletes for maximal health and performance. The goals of the chapter are to provide general education to the practicing clinician; a referral to a sports dietitian is highly recommended for individualized counseling to support individual athlete performance needs.KeywordsNutritionAthletesEnduranceNutritionistsPerformanceNutritional requirementsDietary supplementsSports medicine.
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Sarcopenia is a skeletal muscle disorder that affects the elderly, characterized by loss of muscle volume associated with loss of strength and performance, increasing the risk of fractures, falls, physical disability and mortality. The diagnosis includes DEXA, physical performance tests, anthropometric measurements as calf circumference and strength test using handgrip strenght that check muscle volume, it’s quality and the elderly mobility and balance hability. Nutritional intervention is an essential strategy in the control of sarcopenia and comprises the adequate energy and protein intake, in addition to vitamin D, primarily. In this context, this narrative review aimed to collect current information about the characteristics of sarcopenia, diagnosis methods and nutritional strategies for the treatment. Updates were searched in BVS, PubMed and SciELO databases, technical books, and Brazilian and international consensus. The structured content makes consultation and updating on sarcopenia easier, from diagnosis to the most relevant dietary recommendations for the treatment of the disease.
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.
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.
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.
We aimed to determine the effect of resistance exercise intensity (%1 repetition maximum-1RM) and volume on muscle protein synthesis, anabolic signaling, and myogenic gene expression.
Fifteen men (21+/-1 years; BMI=24.1+/-0.8 kg/m2) performed 4 sets of unilateral leg extension exercise at different exercise loads and/or volumes: 90% of repetition maximum (1RM) until volitional failure (90FAIL), 30% 1RM work-matched to 90%FAIL (30WM), or 30% 1RM performed until volitional failure (30FAIL). Infusion of [ring-13C6] phenylalanine with biopsies was used to measure rates of mixed (MIX), myofibrillar (MYO), and sarcoplasmic (SARC) protein synthesis at rest, and 4 h and 24 h after exercise. Exercise at 30WM induced a significant increase above rest in MIX (121%) and MYO (87%) protein synthesis at 4 h post-exercise and but at 24 h in the MIX only. The increase in the rate of protein synthesis in MIX and MYO at 4 h post-exercise with 90FAIL and 30FAIL was greater than 30WM, with no difference between these conditions; however, MYO remained elevated (199%) above rest at 24 h only in 30FAIL. There was a significant increase in AktSer473 at 24h in all conditions (P=0.023) and mTORSer2448 phosphorylation at 4 h post-exercise (P=0.025). Phosporylation of Erk1/2Tyr202/204, p70S6KThr389, and 4E-BP1Thr37/46 increased significantly (P<0.05) only in the 30FAIL condition at 4 h post-exercise, whereas, 4E-BP1Thr37/46 phosphorylation was greater 24 h after exercise than at rest in both 90FAIL (237%) and 30FAIL (312%) conditions. Pax7 mRNA expression increased at 24 h post-exercise (P=0.02) regardless of condition. The mRNA expression of MyoD and myogenin were consistently elevated in the 30FAIL condition.
These results suggest that low-load high volume resistance exercise is more effective in inducing acute muscle anabolism than high-load low volume or work matched resistance exercise modes.
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.
Muscle protein breakdown (MPB) is increased following resistance exercise, but ingestion of carbohydrate during postexercise recovery can decrease MPB with no effect on muscle protein synthesis (MPS). We sought to determine whether a combination of essential amino acids (EAA) with low carbohydrate or high carbohydrate could effectively reduce MPB following resistance exercise and improve muscle protein net balance (NB). We hypothesized that higher levels of carbohydrate and resulting increases in circulating insulin would inhibit MPB and associated signaling, resulting in augmented NB. Thirteen male subjects were assigned to one of two groups receiving equivalent amounts of EAA (approximately 20 g) but differing carbohydrate levels (low = 30, high = 90 g). Groups ingested nutrients 1 h after an acute bout of leg resistance exercise. Leg phenylalanine kinetics (e.g., MPB, MPS, NB), signaling proteins, and mRNA expression were assessed on successive muscle biopsies using stable isotopic techniques, immunoblotting, and real-time quantitative PCR, respectively. MPB tended to decrease (P < 0.1) and MPS increased (P < 0.05) similarly in both groups following nutrient ingestion. No group differences were observed, but muscle ring finger 1 (MuRF1) protein content and MuRF1 mRNA expression increased following resistance exercise and remained elevated following nutrient ingestion, while autophagy marker (light-chain 3B-II) decreased after nutrient ingestion (P < 0.05). Forkhead box-O3a phosphorylation, total muscle atrophy F-box (MAFbx) protein, and MAFbx and caspase-3 mRNA expression were unchanged. We conclude that the enhanced muscle protein anabolic response detected when EAA+carbohydrate are ingested postresistance exercise is primarily due to an increase in MPS with minor changes in MPB, regardless of carbohydrate dose or circulating insulin level.
While skeletal muscle protein accretion during resistance training (RT)-mediated myofiber hypertrophy is thought to result from upregulated translation initiation signaling, this concept is based on responses to a single bout of unaccustomed resistance exercise (RE) with no measure of hypertrophy across RT. Further, aging appears to affect acute responses to RE, but whether age differences in responsiveness persist during RT leading to impaired RT adaptation is unclear. We therefore tested whether muscle protein fractional synthesis rate (FSR) and Akt/mammalian target of rapamycin (mTOR) signaling in response to unaccustomed RE differed in old vs. young adults, and whether age differences in acute responsiveness were associated with differences in muscle hypertrophy after 16 wk of RT. Fifteen old and 21 young adult subjects completed the 16-wk study. The phosphorylation states of Akt, S6K1, ribosomal protein S6 (RPS6), eukaryotic initiation factor 4E (eIF4E) binding protein (4EBP1), eIF4E, and eIF4G were all elevated (23-199%) 24 h after a bout of unaccustomed RE. A concomitant 62% increase in FSR was found in a subset (6 old, 8 young). Age x time interaction was found only for RPS6 phosphorylation (+335% in old subjects only), while there was an interaction trend (P = 0.084) for FSR (+96% in young subjects only). After 16 wk of RT, gains in muscle mass, type II myofiber size, and voluntary strength were similar in young and old subjects. In conclusion, at the level of translational signaling, we found no evidence of impaired responsiveness among older adults, and for the first time, we show that changes in translational signaling after unaccustomed RE were associated with substantial muscle protein accretion (hypertrophy) during continued RT.
Skeletal muscle glycogen metabolism was investigated in eight male subjects during and after six sets of 70% one repetition maximum (1 RM, I-70) and 35% 1 RM (I-35) intensity weight-resistance leg extension exercise. Total force application to the machine lever arm was determined via a strain gauge and computer interfaced system and was equated between trials. Compared with the I-70 trial, the I-35 trial was characterized by almost double the repetitions (13 +/- 1 vs. 6 +/- 0) and half the peak concentric torque for each repetition (12.4 +/- 0.5 vs. 24.2 +/- 1.0 Nm). After the sixth set, muscle glycogen degradation was similar between I-70 and I-35 trials (47.0 +/- 6.6 and 46.6 +/- 6.0 mmol/kg wet wt, respectively), as was muscle lactate accumulation (13.8 +/- 0.7 and 16.7 +/- 4.2 mmol/kg wet wt, respectively). After 2 h of passive recovery without caloric intake, muscle glycogen increased by 22.2 +/- 6.8 and 14.2 +/- 2.5 mmol/kg wet wt in the I-70 and I-35 trials, respectively. Optical absorbance measurement of periodic acid-Schiff-stained muscle sections after the 2 h of recovery revealed larger absorbance increases in fast-twitch than in slow-twitch fibers (0.119 +/- 0.024 and 0.055 +/- 0.024, P = 0.02). Data indicated that when external work was constant, the absolute amount of muscle glycogenolysis was the same regardless of the intensity of resistance exercise. Nevertheless the rate of glycogenolysis during the I-70 trial was approximately double that of the I-35 trial.
It has been shown that muscle protein synthetic rate (MPS) is elevated in humans by 50% at 4 hrs following a bout of heavy resistance training, and by 109% at 24 hrs following training. This study further examined the time course for elevated muscle protein synthesis by examining its rate at 36 hrs following a training session. Six healthy young men performed 12 sets of 6- to 12-RM elbow flexion exercises with one arm while the opposite arm served as a control. MPS was calculated from the in vivo rate of incorporation of L-[1,2-13C2] leucine into biceps brachii of both arms using the primed constant infusion technique over 11 hrs. At an average time of 36 hrs postexercise, MPS in the exercised arm had returned to within 14% of the control arm value, the difference being nonsignificant. It is concluded that following a bout of heavy resistance training, MPS increases rapidly, is more than double at 24 hrs, and thereafter declines rapidly so that at 36 hrs it has almost returned to baseline.
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.
We hypothesized a differential activation of the anabolic signaling proteins protein kinase B (PKB) and p70 S6 kinase (p70(S6K)) and subsequent differential stimulation of human muscle protein synthesis (MPS) after dynamic shortening or lengthening exercise. Eight healthy men [25 +/- 5 yr, BMI 26 +/- 3 kg/m(-2) (means +/- SD)] were studied before and after 12 min of repeated stepping up to knee height, and down again, while carrying 25% of their body weight, i.e., shortening exercise with the "up" leg and lengthening exercise with contralateral "down" leg. Quadriceps biopsies were taken before and 3, 6, and 24 h after exercise. After exercise, over 2 h before the biopsies, the subjects ingested 500 ml of water containing 45 g of essential amino acids and 135 g of sucrose. Rates of muscle protein synthesis were determined via incorporation over time of [1-(13)C]leucine (<or=6 h after exercise) or [1-(13)C]valine (21-24 h after exercise) and phosphorylation of signaling proteins by Western analysis. PKB and p70(S6K) phosphorylation increased approximately 3-fold after 3 h and remained elevated at 6 and 24 h. After exercise, rates of myofibrillar and sarcoplasmic protein synthesis were unchanged over the period including exercise and 3 h of recovery but had increased significantly at 6 (approximately 3.0- and 2.4-fold, respectively) and 24 h (approximately 3.2- and 2.0-fold, respectively), independently of the mode of exercise. Short-term dynamic exercise in either shortening or lengthening mode increases MPS at least as much as resistance exercise and is associated with long-term activation of PKB and p70(S6K).
Muscle protein metabolism is resistant to insulin's anabolic effect in healthy older subjects. This is associated with reduced insulin vasodilation. We hypothesized that aerobic exercise restores muscle protein anabolism in response to insulin by improving vasodilation in older subjects. We measured blood flow, endothelin-1, Akt/mammalian target of rapamycin (mTOR) signaling, and muscle protein kinetics in response to physiological local hyperinsulinemia in two groups of older subjects following a bout of aerobic exercise (EX group: aged 70 +/- 2 years; 45-min treadmill walk, 70% heart rate max) or rest (CTRL group: aged 68 +/- 1 years). Baseline endothelin-1 was lower and blood flow tended to be higher in the EX group, but protein kinetics was not different between groups. Insulin decreased endothelin-1 (P < 0.05) in both groups, but endothelin-1 remained higher in the CTRL group (P < 0.05) and blood flow increased only in the EX group (EX group: 3.8 +/- 0.7 to 5.3 +/- 0.8; CTRL group: 2.5 +/- 0.2 to 2.6 +/- 0.2 ml x min(-1) x 100 ml leg(-1)). Insulin improved Akt phosphorylation in the EX group and increased mTOR/S6 kinase 1 phosphorylation and muscle protein synthesis (EX group: 49 +/- 11 to 89 +/- 23; CTRL group: 58 +/- 8 to 57 +/- 12 nmol x min(-1) x 100 ml leg(-1)) in the EX group only (P < 0.05). Because breakdown did not change, net muscle protein balance became positive only in the EX group (P < 0.05). In conclusion, a bout of aerobic exercise restores the anabolic response of muscle proteins to insulin by improving endothelial function and Akt/mTOR signaling in older subjects.
We recently showed that resistance exercise and ingestion of essential amino acids with carbohydrate (EAA+CHO) can independently stimulate mammalian target of rapamycin (mTOR) signaling and muscle protein synthesis in humans. Providing an EAA+CHO solution postexercise can further increase muscle protein synthesis. Therefore, we hypothesized that enhanced mTOR signaling might be responsible for the greater muscle protein synthesis when leucine-enriched EAA+CHOs are ingested during postexercise recovery. Sixteen male subjects were randomized to one of two groups (control or EAA+CHO). The EAA+CHO group ingested the nutrient solution 1 h after resistance exercise. mTOR signaling was assessed by immunoblotting from repeated muscle biopsy samples. Mixed muscle fractional synthetic rate (FSR) was measured using stable isotope techniques. Muscle protein synthesis and 4E-BP1 phosphorylation during exercise were significantly reduced (P < 0.05). Postexercise FSR was elevated above baseline in both groups at 1 h but was even further elevated in the EAA+CHO group at 2 h postexercise (P < 0.05). Increased FSR was associated with enhanced phosphorylation of mTOR and S6K1 (P < 0.05). Akt phosphorylation was elevated at 1 h and returned to baseline by 2 h in the control group, but it remained elevated in the EAA+CHO group (P < 0.05). 4E-BP1 phosphorylation returned to baseline during recovery in control but became elevated when EAA+CHO was ingested (P < 0.05). eEF2 phosphorylation decreased at 1 and 2 h postexercise to a similar extent in both groups (P < 0.05). Our data suggest that enhanced activation of the mTOR signaling pathway is playing a role in the greater synthesis of muscle proteins when resistance exercise is followed by EAA+CHO ingestion.
We analysed the effects of resistance exercise upon the phosphorylation state of proteins associated with adaptive processes from the Akt/PKB (protein kinase B) and the mitogen-activated protein kinase (MAPK) pathways. Nine healthy young men (21.7 +/- 0.55 year) performed 10 sets of 10 leg extensions at 80% of their 1-RM (repetition maximum). Muscle biopsies were taken from the vastus lateralis at rest, within the first 30 s after exercise and at 24 h post-exercise. Immediately post exercise, the phosphorylation states of Akt/PKB on Thr308 and Ser473 and 4E-BP1 on Thr37/46 (eukaryotic initiation factor 4E-binding protein 1) were decreased (-60 to -90%, P < 0.05). Conversely, the phosphorylation of p70(s6k) (p70 ribosomal S6 kinase) on Thr421/Ser424 was increased more than 20-fold (P < 0.05), and this was associated with a 10- to 50-fold increase in the phosphorylation of p38 and ERK1/2 (extracellular signal-regulated kinase) (P < 0.05). Twenty-four hours post-exercise the phosphorylation state of Akt/PKB on Thr308 was depressed, whereas the phosphorylation of p70(s6k) on Thr421/Ser424 and sarcoplasmic ERK1/2 were elevated. The present results indicate that high-intensity resistance exercise in the fasted state inhibits Akt/PKB and 4E-BP1 whilst concomitantly augmenting MAPK signalling and p70(s6k) on Thr421/Ser424.
We determined the effects of intravenous infusion of amino acids (AA) at serum insulin of 5, 30, 72, and 167 mU/l on anabolic signaling, expression of ubiquitin-proteasome components, and protein turnover in muscles of healthy young men. Tripling AA availability at 5 mU/l insulin doubled incorporation of [1-(13)C]leucine [i.e., muscle protein synthesis (MPS), P < 0.01] without affecting the rate of leg protein breakdown (LPB; appearance of d(5)-phenylalanine). While keeping AA availability constant, increasing insulin to 30 mU/l halved LPB (P < 0.05) without further inhibition at higher doses, whereas rates of MPS were identical to that at 5 mU/l insulin. The phosphorylation of PKB Ser(473) and p70(S6k) Thr(389) increased concomitantly with insulin, but whereas raising insulin to 30 mU/l increased the phosphorylation of mTOR Ser(2448), 4E-BP1 Thr(37/46), or GSK3beta Ser(9) and decreased that of eEF2 Thr(56), higher insulin doses to 72 and 167 mU/l did not augment these latter responses. MAFbx and proteasome C2 subunit proteins declined as insulin increased, with MuRF-1 expression largely unchanged. Thus increasing AA and insulin availability causes changes in anabolic signaling and amounts of enzymes of the ubiquitin-proteasome pathway, which cannot be easily reconciled with observed effects on MPS or LPB.
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.
Aging is associated with a decline in strength, endurance, balance, and mobility. Obesity worsens the age-related impairment in physical function and often leads to frailty. The American College of Sports Medicine recommends a multicomponent (strength, endurance, flexibility, and balance) exercise program to maintain physical fitness. However, the effect of such an exercise program on physical fitness in frail, obese older adults is not known. We therefore determined the effect of a 3-month long multicomponent exercise training program, on endurance (peak aerobic capacity (VO(2) peak)), muscle strength, muscle mass, and the rate of muscle protein synthesis (basal rate and anabolic response to feeding) in nine 65- to 80-year-old, moderately frail, obese older adults. After 3 months of training, fat mass decreased (P < 0.05) whereas fat-free mass (FFM), appendicular lean body mass, strength, and VO(2) peak increased (all P < 0.05). Regular strength and endurance exercise increased the mixed muscle protein fractional synthesis rate (FSR) but had no effect on the feeding-induced increase in muscle protein FSR (~0.02%/h increase from basal values both before and after exercise training; effect of feeding: P = 0.02; effect of training: P = 0.047; no interaction: P = 0.84). We conclude that: (i) a multicomponent exercise training program has beneficial effects on muscle mass and physical function and should therefore be recommended to frail, obese older adults, and (ii) regular multicomponent exercise increases the basal rate of muscle protein synthesis without affecting the magnitude of the muscle protein anabolic response to feeding.
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.
Sex differences are evident in human skeletal muscle as the cross-sectional area of individual muscle fibres is greater in men than in women. We have recently shown that resistance exercise stimulates mammalian target of rapamycin (mTOR) signalling and muscle protein synthesis in humans during early post-exercise recovery. Therefore, the aim of this study was to determine if sex influences the muscle protein synthesis response during recovery from resistance exercise.
Seventeen subjects, nine male and eight female, were studied in the fasted state before, during and for 2 h following a bout of high-intensity leg resistance exercise. Mixed muscle protein fractional synthetic rate was measured using stable isotope techniques and mTOR signalling was assessed by immunoblotting from repeated vastus lateralis muscle biopsy samples.
Post-exercise muscle protein synthesis increased by 52% in the men and by 47% in the women (P < 0.05) and was not different between groups (P > 0.05). Akt phosphorylation increased in both groups at 1 h post-exercise (P < 0.05) and returned to baseline during 2 h post-exercise with no differences between groups (P > 0.05). Phosphorylation of mTOR and its downstream effector S6K1 increased significantly and similarly between groups during post-exercise recovery (P < 0.05). eEF2 phosphorylation decreased at 1- and 2 h post-exercise (P < 0.05) to a similar extent in both groups.
The contraction-induced increase in early post-exercise mTOR signalling and muscle protein synthesis is independent of sex and appears to not play a role in the sexual dimorphism of leg skeletal muscle in young men and women.
We aimed to determine whether exercise-induced elevations in systemic concentration of testosterone, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) enhanced post-exercise myofibrillar protein synthesis (MPS) and phosphorylation of signalling proteins important in regulating mRNA translation. Eight young men (20 +/- 1.1 years, BMI = 26 +/- 3.5 kg m(-2)) completed two exercise protocols designed to maintain basal hormone concentrations (low hormone, LH) or elicit increases in endogenous hormones (high hormone, HH). In the LH protocol, participants performed a bout of unilateral resistance exercise with the elbow flexors. The HH protocol consisted of the same elbow flexor exercise with the contralateral arm followed immediately by high-volume leg resistance exercise. Participants consumed 25 g of protein after arm exercise to maximize MPS. Muscle biopsies and blood samples were taken as appropriate. There were no changes in serum testosterone, GH or IGF-1 after the LH protocol, whereas there were marked elevations after HH (testosterone, P < 0.001; GH, P < 0.001; IGF-1, P < 0.05). Exercise stimulated a rise in MPS in the biceps brachii (rest = 0.040 +/- 0.007, LH = 0.071 +/- 0.008, HH = 0.064 +/- 0.014% h(-1); P < 0.05) with no effect of elevated hormones (P = 0.72). Phosphorylation of the 70 kDa S6 protein kinase (p70S6K) also increased post-exercise (P < 0.05) with no differences between conditions. We conclude that the transient increases in endogenous purportedly anabolic hormones do not enhance fed-state anabolic signalling or MPS following resistance exercise. Local mechanisms are likely to be of predominant importance for the post-exercise increase in MPS.
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.
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.
Muscle contraction during exercise, whether resistive or endurance in nature, has profound affects on muscle protein turnover that can persist for up to 72 h. It is well established that feeding during the postexercise period is required to bring about a positive net protein balance (muscle protein synthesis - muscle protein breakdown). There is mounting evidence that the timing of ingestion and the protein source during recovery independently regulate the protein synthetic response and influence the extent of muscle hypertrophy. Minor differences in muscle protein turnover appear to exist in young men and women; however, with aging there may be more substantial sex-based differences in response to both feeding and resistance exercise. The recognition of anabolic signaling pathways and molecules are also enhancing our understanding of the regulation of protein turnover following exercise perturbations. In this review we summarize the current understanding of muscle protein turnover in response to exercise and feeding and highlight potential sex-based dimorphisms. Furthermore, we examine the underlying anabolic signaling pathways and molecules that regulate these processes.
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.
Studies of protein metabolism with stable isotopes require determination of the 'natural' isotopic enrichment in tissues. This has previously been determined by taking a pre-test muscle biopsy or by using the isotopic enrichment of a separate control group of subjects. In this study we have measured and compared the 'natural' 13C enrichment of leucine in plasma protein and muscle protein in 14 subjects. The mean enrichment of leucine (delta 13CPDB) in muscle protein, -26.627, was not significantly different from that in plasma protein, -27.152. The data indicate that the 13C enrichment of leucine in plasma protein reflects that of muscle protein and provides an attractive alternative to an additional muscle biopsy in studies of protein metabolism with stable isotopes.
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.
This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.
The calf muscles, compared with the thigh, are less responsive to resistance exercise in ambulatory and bed-rested individuals, apparently due to muscle-specific differences in protein metabolism. We chose to evaluate the efficacy of using amino acids to elevate protein synthesis in the soleus, because amino acids have been shown to have a potent anabolic effect in the vastus lateralis. Mixed muscle protein synthesis in the soleus and vastus lateralis was measured before and after infusion of mixed amino acids in 10 individuals (28 +/- 1 yr). Phosphorylation of ribosomal protein p70 S6 kinase (p70S6K; Thr389) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1; Thr37/46) was also evaluated at rest and after 3 h of amino acid infusion. Basal protein synthesis was similar (P = 0.126), and amino acids stimulated protein synthesis to a similar extent (P = 0.004) in the vastus lateralis (0.043 +/- 0.011%/h) and soleus (0.032 +/- 0.017%/h). Phosphorylation of p70S6K (P = 0.443) and 4E-BP1 (P = 0.192) was not increased in either muscle; however, the soleus contained more total (P = 0.002) and phosphorylated (P = 0.013) 4E-BP1 than the vastus lateralis. These data support the need for further study of amino acid supplementation as a means to compensate for the reduced effectiveness of calf resistance exercise in ambulatory individuals and those exposed to extended periods of unloading. The greater 4E-BP1 in the soleus suggests that there is a muscle-specific distribution of general translational initiation machinery in human skeletal muscle.
We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque = 225 +/- 7 N.m, means +/- SE) or lengthening contractions (LC; average peak torque = 299 +/- 18 N.m) with equivalent work performed in each mode. Eight healthy young men (21.9 +/- 0.6 yr, body mass index 24.9 +/- 1.3 kg/m2) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 +/- 0.7 vs. 10.9 +/- 0.8 kJ, P = 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g.kg(-1).h(-1) of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P < 0.01). The increases (P < 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC.
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.
Timing of nutrient ingestion has been demonstrated to influence the anabolic response of muscle following exercise. Previously, we demonstrated that net amino acid uptake was greater when free essential amino acids plus carbohydrates were ingested before resistance exercise rather than following exercise. However, it is unclear if ingestion of whole proteins before exercise would stimulate a superior response compared with following exercise. This study was designed to examine the response of muscle protein balance to ingestion of whey proteins both before and following resistance exercise. Healthy volunteers were randomly assigned to one of two groups. A solution of whey proteins was consumed either immediately before exercise (PRE; n = 8) or immediately following exercise (POST; n = 9). Each subject performed 10 sets of 8 repetitions of leg extension exercise. Phenylalanine concentrations were measured in femoral arteriovenous samples to determine balance across the leg. Arterial amino acid concentrations were elevated by approximately 50%, and net amino acid balance switched from negative to positive following ingestion of proteins at either time. Amino acid uptake was not significantly different between PRE and POST when calculated from the beginning of exercise (67 +/- 22 and 27 +/- 10 for PRE and POST, respectively) or from the ingestion of each drink (60 +/- 17 and 63 +/- 15 for PRE and POST, respectively). Thus the response of net muscle protein balance to timing of intact protein ingestion does not respond as does that of the combination of free amino acids and carbohydrate.
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.
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.
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.
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).
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.
The mammalian target of rapamycin (mTOR) and AMP‐activated protein kinase (AMPK) are important nutrient‐ and energy‐sensing and signalling proteins in skeletal muscle. AMPK activation decreases muscle protein synthesis by inhibiting mTOR signalling to regulatory proteins associated with translation initiation and elongation. On the other hand, essential amino acids (leucine in particular) and insulin stimulate mTOR signalling and protein synthesis. We hypothesized that anabolic nutrients would be sensed by both AMPK and mTOR, resulting in an acute and potent stimulation of human skeletal muscle protein synthesis via enhanced translation initiation and elongation.
We measured muscle protein synthesis and mTOR‐associated upstream and downstream signalling proteins in young male subjects ( n = 14) using stable isotopic and immunoblotting techniques. Following a first muscle biopsy, subjects in the ‘Nutrition’ group ingested a leucine‐enriched essential amino acid–carbohydrate mixture (EAC). Subjects in the Control group did not consume nutrients. A second biopsy was obtained 1 h later. Ingestion of EAC significantly increased muscle protein synthesis, modestly reduced AMPK phosphorylation, and increased Akt/PKB (protein kinase B) and mTOR phosphorylation ( P < 0.05). mTOR signalling to its downstream effectors (S6 kinase 1 (S6K1) and 4E‐binding protein 1 (4E‐BP1) phosphorylation status) was also increased ( P < 0.05). In addition, eukaryotic elongation factor 2 (eEF2) phosphorylation was significantly reduced ( P < 0.05). Protein synthesis and cell signalling (phosphorylation status) was unchanged in the control group ( P > 0.05).
We conclude that anabolic nutrients alter the phosphorylation status of both AMPK‐ and mTOR‐associated signalling proteins in human muscle, in association with an increase in protein synthesis not only via enhanced translation initiation but also through signalling promoting translation elongation.
Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise 572 Burd et al. at McMaster Univ on May 5, 2011 jn.nutrition.org Downloaded from 5 Postexercise net protein synthesis in human muscle from orally administered amino acids
- Elliott Kd Tipton
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Tipton KD, Elliott TA, Cree MG, Aarsland AA, Sanford AP, Wolfe RR. Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise. Am J Physiol Endocrinol Metab. 2007;292: E71–6. 572 Burd et al. at McMaster Univ on May 5, 2011 jn.nutrition.org Downloaded from 5. Tipton KD, Ferrando AA, Phillips SM, Doyle D Jr, Wolfe RR. Postexercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol. 1999;276:E628–34.
Natural Sciences and Engineering Research Council of Canada, Social Sciences and Humanities Research Council of Canada, Tri-Council policy statement: ethical conduct for research involving humans
Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada, Social Sciences and Humanities
Research Council of Canada, Tri-Council policy statement: ethical
conduct for research involving humans. 2010.