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Abstract

From the breakthrough studies of dietary carbohydrate and exercise capacity in the 1960s through to the more recent studies of cellular signaling and the adaptive response to exercise in muscle, it has become apparent that manipulations of dietary fat and carbohydrate within training phases, or in the immediate preparation for competition, can profoundly alter the availability and utilization of these major fuels and, subsequently, the performance of endurance sport (events >30 min up to ∼24 hr). A variety of terms have emerged to describe new or nuanced versions of such exercise-diet strategies (e.g., train low, train high, low-carbohydrate high-fat diet, periodized carbohydrate diet). However, the nonuniform meanings of these terms have caused confusion and miscommunication, both in the popular press and among the scientific community. Sports scientists will continue to hold different views on optimal protocols of fuel support for training and competition in different endurance events. However, to promote collaboration and shared discussions, a commonly accepted and consistent terminology will help to strengthen hypotheses and experimental/experiential data around various strategies. We propose a series of definitions and explanations as a starting point for a more unified dialogue around acute and chronic manipulations of fat and carbohydrate in the athlete's diet, noting philosophies of approaches rather than a single/definitive macronutrient prescription. We also summarize some of the key questions that need to be tackled to help produce greater insight into this exciting area of sports nutrition research and practice.

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... Meanwhile, meals are consumed soon after training sessions and high-intensity track sessions are completed as a mid-morning workout after breakfast [110][111][112][113][114]. Although it is unlikely that recreational athletes will have interest in adopting East African dietary practices per se, some principles such as the periodization of carbohydrate availability around training sessions are topical [115], and merit further comment. It is also worth noting that, against a background of minimal use of dietary supplements [116], elite East African athletes have been targeted for the use and marketing of new sports foods (drinks and gels), designed to increase the consumption and muscle delivery of carbohydrate during endurance sports [117,118]. ...
... Furthermore, there is no evidence of cause and effect, and the frailties of the current literature, at least as has been examined in relation to sports nutrition, include the lack of Table 2 Considerations for the elite athlete in considering the specific evidence base for the value of sports science strategies. Undertaking endurance exercise with low glycogen stores or prolonging its post-exercise restoration may upregulate or amplify the signaling cascades that underpin mitochondrial biogenesis and increased capacity for muscle fat oxidation [115]. A thoughtful combination of training and dietary sequences, which integrates high quality sessions with high carbohydrate availability, delayed refueling ("sleep low") and low-moderate intensity sessions undertaken with low carbohydrate availability may enhance the overall training outcomes, leading to enhanced performance [115]. ...
... Undertaking endurance exercise with low glycogen stores or prolonging its post-exercise restoration may upregulate or amplify the signaling cascades that underpin mitochondrial biogenesis and increased capacity for muscle fat oxidation [115]. A thoughtful combination of training and dietary sequences, which integrates high quality sessions with high carbohydrate availability, delayed refueling ("sleep low") and low-moderate intensity sessions undertaken with low carbohydrate availability may enhance the overall training outcomes, leading to enhanced performance [115]. ...
... Según las estrategias de nutrición contemporáneas, esa ingesta previa es particularmente importante para eventos que se realizan en la mañana, cómo en el presente estudio (6:00 am), donde la ingesta de carbohidratos puede restaurar el glucógeno hepático después de un ayuno nocturno, así como proporcionar suministro continuo de energía para la actividad (8,18). Es importante mencionar que las estrategias para almacenar glucógeno previas al evento no dependen únicamente de la ingesta previa; sino que se asocian a las ingestas de carbohidratos durante las 24 horas antes (19,20). Esto último pudo ser una de las principales limitantes del estudio ya que no se controló la ingesta alimentaria de los participantes que pudiera contribuir a la supercompensación de glucógeno teniendo un impacto en el rendimiento y en los resultados obtenidos de percepción del esfuerzo. ...
... Por otro lado, la ingesta de carbohidratos durante el ejercicio puede mejorar el rendimiento por medio de la entrega de sustratos adicionales frente a la disminución de las reservas endógenas, así como la prevención de la hipoglucemia y la activación de centros de recompensa en el sistema nervioso central (2,19). Existen ya directrices que recomiendan el consumo de 30-60-90 gramos por hora, incluso 120 gramos por hora en deportes de ultra resistencia (21,22). ...
Article
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Introducción: Una ingesta óptima de carbohidratos permite un buen desempeño y recuperación en deportes de resistencia como en el ciclismo de ruta. Objetivo: Evaluar la percepción del esfuerzo según los criterios de “la escala de Borg” bajo la implementación de acompañamiento nutricional que controla de manera individual la ingesta de carbohidratos en los momentos del antes y el durante un entrenamiento de resistencia de 4 horas de duración, en ciclistas aficionados. Materiales y métodos: Se realizó una investigación evaluativa, con dos momentos de medición transversal; uno sin acompañamiento nutricional y un segundo momento, con prescripción alimentaria para el antes y durante un entrenamiento. Para ello, se seleccionaron por conveniencia 8 ciclistas recreativos de la ciudad de Medellín. Resultados: No se mostraron diferencias estadísticamente significativas en la percepción del esfuerzo tras la prescripción de carbohidratos para el antes y durante, respecto a la percepción del esfuerzo obtenida previa a dicha prescripción. Conclusión: Como principal hallazgo se identificaron variables metabólicas y de composición que pueden ser tenidas en cuenta en futuras intervenciones para establecer correlaciones fisiológicas y de alimentación en deportes de resistencia.
... However, there are limited methods of assessing carbohydrate utilization during a given workout, leaving athletes and practitioners unclear as to how much carbohydrate or energy should be repleted. Indeed, there have been recent calls for a better understanding of the fuel costs and associated carbohydrate requirements of various training sessions commonly undertaken by athletes [2]. Based on the close relationship between mechanical work output and metabolic energy expenditure [3], it is plausible that readily-available measures of exercise quantification (i.e., training load) could be used to model and predict carbohydrate utilization during exercise, particularly when combined with other measures obtained from traditional laboratory testing. ...
... These calculations result in the following values: [2], rer = wingate_avg_rer ) %>% select(-vo2) %>% pivot_longer(m:f, names_to = "sex", values_to = "vo2") %>% nest(.by = sex) %>% left_join(Esbj_vo2max_tbl %>% select(sex, vo2max_l), by = "sex") %>% unnest(data) %>% mutate(pct_max = vo2/vo2max_l) %>% nest(.by ...
... The benefits of intra-exercise carbohydrate fuelling are well established [7]. Although mostly based on male data, results from studies including female athletes show similar metabolic responses as well as an ergogenic effect across all phases of the menstrual cycle [40,70]. ...
... In male athletes, manipulation of carbohydrate intake to include some restricted states can stimulate cellular adaptation, but this must be balanced with carbohydrate availability for training quality [7]. More female-specific research is needed to see whether these techniques are beneficial, neutral or maladaptive [47]. ...
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Despite growing participation, there is limited research into the nutritional needs of climbers and none specific to female climbers. Female athletes in general are still significantly under-represented in sport and nutritional science research. The physiological requirements of climbing are extensive and variable, demanding both highly developed anaerobic and aerobic energy systems. Finger strength, upper body power and training hours have been highlighted as the key determinants of climbing performance in females. Nutritional implications of this include adequate energy and carbohydrate availability, appropriate protein intake and timing for recovery, and use of specific supplements. As a weight sensitive sport, energy intake and availability are key areas of consideration for female climbers' health and performance. Consideration of macronutrient intake and timing with an understanding of sex hormone interaction across the menstrual cycle confers some considerations to nutritional guidelines. Micronutrients of particular interest to the female climber include iron, vitamin D and calcium. Appropriate supplement use may be beneficial, however more research is needed to provide any female specific dosing strategies. It may be premature to prescribe generalised female specific nutrition recommendations for climbers. A personalised approach that considers the indi-vidual's menstrual cycle and experience is recommended. Further research into nutrition for the female climber is warranted.
... The performance of sport and other physical activities, particularly those involving prolonged submaximal or intermittent highintensity exercise, is impaired by low carbohydrate (CHO) availability (Karelis et al., 2010), which is defined as an insufficient glycogen concentration and inadequate blood glucose (BG) supply in comparison with the fuel needs of an exercise session (Burke, Hawley, et al., 2018;Impey et al., 2018). Targets for CHO intake, to optimize performance and support health and well-being, in the everyday diet and during competition are a prominent feature of sports nutrition guidelines (Thomas, Erdman, et al., 2016). ...
... Targets for CHO intake, to optimize performance and support health and well-being, in the everyday diet and during competition are a prominent feature of sports nutrition guidelines (Thomas, Erdman, et al., 2016). The evolution of these guidelines has included the concept of specificity to the athlete and to the exercise scenario (personalization) and differences in intake between and within days according to the fuel requirements and goals of each session of exercise (periodization; Burke, Hawley, et al., 2018;Impey et al., 2018). More recently, sports nutrition guidelines have incorporated recommendations relating to energy availability (EA), matching energy intake (EI) according to the energy demands of exercise to ensure that body metabolism and function are optimized (Mountjoy et al., 2018). ...
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This review discusses the potential value of tracking interstitial glucose with continuous glucose monitors (CGMs) in athletes, highlighting possible applications and important considerations in the collection and interpretation of interstitial glucose data. CGMs are sensors that provide real time, longitudinal tracking of interstitial glucose with a range of commercial monitors currently available. Recent advancements in CGM technology have led to the development of athlete-specific devices targeting glucose monitoring in sport. Although largely untested, the capacity of CGMs to capture the duration, magnitude, and frequency of interstitial glucose fluctuations every 1–15 min may present a unique opportunity to monitor fueling adequacy around competitive events and training sessions, with applications for applied research and sports nutrition practice. Indeed, manufacturers of athlete-specific devices market these products as a “fueling gauge,” enabling athletes to “push their limits longer and get bigger gains.” However, as glucose homeostasis is a complex phenomenon, extensive research is required to ascertain whether systemic glucose availability (estimated by CGM-derived interstitial glucose) has any meaning in relation to the intended purposes in sport. Whether CGMs will provide reliable and accurate information and enhance sports nutrition knowledge and practice is currently untested. Caveats around the use of CGMs include technical issues (dislodging of sensors during periods of surveillance, loss of data due to synchronization issues), practical issues (potential bans on their use in some sporting scenarios, expense), and challenges to the underpinning principles of data interpretation, which highlight the role of sports nutrition professionals to provide context and interpretation.
... From a practical perspective, this so-called "trainlow" paradigm has been translated as "fuelling for the work required" whereby daily CHO intake is adjusted day-by-day and meal-by-meal according to the upcoming activity and the desired outcome of the exercise session i.e., promoting exercise intensity versus stimulating metabolic adaptations (Impey et al., 2018). Although such models of nutritional periodization are gaining increased recognition amongst endurance sports (Burke et al., 2018;Impey et al., 2018;Stellingwerff et al., 2019), no such models have yet been developed for the professional soccer player. ...
... Nonetheless, we previously observed that commencing high-intensity intermittent running (using a model aligned to the training-intensities associated with small sided games, i.e., 6 × 3 min bouts of running completed at 85-90% VO 2max ) with reduced pre-exercise muscle glycogen (and without provision of CHO during exercise) augments training-induced up-regulation of oxidative enzyme activity in both the gastrocnemius and vastus lateralis muscle, as compared with conditions considered of normal pre-exercise muscle glycogen and consumption of CHO during training (Morton et al., 2009). It should also be noted, however, that many of the previous models of CHO periodization studied within the literature have incorporated models of CHO restriction that may not always be practically applicable to the professional player, e.g., training twice per day with limited recovery between sessions, training late in the evening followed by a fasted training session on the subsequent morning (the so-called sleep-low train-low model) etc. (see Impey et al., 2018;Burke et al., 2018 for a detailed discussion of such models). ...
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Despite more than four decades of research examining the physical demands of match-play, quantification of the customary training loads of adult male professional soccer players is comparatively recent. The training loads experienced by players during weekly micro-cycles are influenced by phase of season, player position, frequency of games, player starting status, player-specific training goals and club coaching philosophy. From a macronutrient perspective, the periodization of physical loading within (i.e., match versus training days) and between contrasting micro-cycles (e.g., 1, 2 or 3 games per week schedules) has implications for daily carbohydrate (CHO) requirements. Indeed, aside from the well-recognised role of muscle glycogen as the predominant energy source during match-play, it is now recognised that the glycogen granule may exert regulatory roles in activating or attenuating the molecular machinery that modulate skeletal muscle adaptations to training. With this in mind, the concept of CHO periodization is gaining in popularity, whereby CHO intake is adjusted day-by-day and meal-by-meal according to the fuelling demands and specific goals of the upcoming session. On this basis, the present paper provides a contemporary overview and theoretical framework for which to periodize CHO availability for the professional soccer player according to the "fuel for the work" paradigm.
... The importance of muscle carbohydrate stores (glycogen) as an energy substrate during exercise was first recognised in the 1960s [136], with subsequent research and practice confirming high carbohydrate availability (matching of total body carbohydrate stores to the fuel cost of exercise) as a key determinant of the performance of higher-intensity endurance exercise [137]. Meanwhile, glycogen availability has more recently been recognised for its regulatory role in exercise signalling pathways and the inter-organ crosstalk associated with exercise. ...
Article
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Following anterior cruciate ligament (ACL) injury, quadriceps muscle atrophy persists despite rehabilitation, leading to loss of lower limb strength, osteoarthritis, poor knee joint health and reduced quality of life. However, the molecular mechanisms responsible for these deficits in hypertrophic adaptations within the quadriceps muscle following ACL injury and reconstruction are poorly understood. While resistance exercise training stimulates skeletal muscle hypertrophy, attenuation of these hypertrophic pathways can hinder rehabilitation following ACL injury and reconstruction, and ultimately lead to skeletal muscle atrophy that persists beyond ACL reconstruction, similar to disuse atrophy. Numerous studies have documented beneficial roles of nutritional support, including nutritional supplementation, in maintaining and/or increasing muscle mass. There are three main mechanisms by which nutritional supplementation may attenuate muscle atrophy and promote hypertrophy: (1) by directly affecting muscle protein synthetic machinery; (2) indirectly increasing an individual’s ability to work harder; and/or (3) directly affecting satellite cell proliferation and differentiation. We propose that nutritional support may enhance rehabilitative responses to exercise training and positively impact molecular machinery underlying muscle hypertrophy. As one of the fastest growing knee injuries worldwide, a better understanding of the potential mechanisms involved in quadriceps muscle deficits following ACL injury and reconstruction, and potential benefits of nutritional support, are required to help restore quadriceps muscle mass and/or strength. This review discusses our current understanding of the molecular mechanisms involved in muscle hypertrophy and disuse atrophy, and how nutritional supplements may leverage these pathways to maximise recovery from ACL injury and reconstruction.
... However, there are limited methods of assessing carbohydrate utilization during a given workout, leaving athletes and practitioners unclear as to how much carbohydrate or energy should be repleted. Indeed, there have been recent calls for a better understanding of the fuel costs and associated carbohydrate requirements of various training sessions commonly undertaken by athletes [2]. Based on the close relationship between mechanical work output and metabolic energy expenditure [3], it is plausible that readily available measures of exercise quantification (i.e., training load) could be used to model and predict carbohydrate utilization during exercise, particularly when combined with other measures obtained from traditional laboratory testing. ...
Article
Full-text available
Background Sports nutrition guidelines recommend carbohydrate (CHO) intake be individualized to the athlete and modulated according to changes in training load. However, there are limited methods to assess CHO utilization during training sessions. Objectives We aimed to (1) quantify bivariate relationships between both CHO and overall energy expenditure (EE) during exercise and commonly used, non-invasive measures of training load across sessions of varying duration and intensity and (2) build and evaluate prediction models to estimate CHO utilization and EE with the same training load measures and easily quantified individual factors. Methods This study was undertaken in two parts: a primary study, where participants performed four different laboratory-based cycle training sessions, and a validation study where different participants performed a single laboratory-based training session using one of three exercise modalities (cycling, running, or kayaking). The primary study included 15 cyclists (five female; maximal oxygen consumption [V˙V˙\dot{V}O2max], 51.9 ± 7.2 mL/kg/min), the validation study included 21 cyclists (seven female; V˙V˙\dot{V}O2max 53.5 ± 11.0 mL/kg/min), 20 runners (six female; V˙V˙\dot{V}O2max 57.5 ± 7.2 mL/kg/min), and 18 kayakers (five female; V˙V˙\dot{V}O2max 45.6 ± 4.8 mL/kg/min). Training sessions were quantified using six training load metrics: two using heart rate, three using power, and one using perceived exertion. Carbohydrate use and EE were determined separately for aerobic (gas exchange) and anaerobic (net lactate accumulation, body mass, and O2 lactate equivalent method) energy systems and summed. Repeated-measures correlations were used to examine relationships between training load and both CHO utilization and EE. General estimating equations were used to model CHO utilization and EE, using training load alongside measures of fitness and sex. Models were built in the primary study and tested in the validation study. Model performance is reported as the coefficient of determination (R²) and mean absolute error, with measures of calibration used for model evaluation and for sport-specific model re-calibration. Results Very-large to near-perfect within-subject correlations (r = 0.76–0.96) were evident between all training load metrics and both CHO utilization and EE. In the primary study, all models explained a large amount of variance (R² = 0.77–0.96) and displayed good accuracy (mean absolute error; CHO = 16–21 g [10–14%], EE = 53–82 kcal [7–11%]). In the validation study, the mean absolute error ranged from 16–50 g [15–45%] for CHO models to 53–182 kcal [9–31%] for EE models. The calibrated mean absolute error ranged from 9–20 g [8–18%] for CHO models to 36–72 kcal [6–12%] for EE models. Conclusions At the individual level, there are strong linear relationships between all measures of training load and both CHO utilization and EE during cycling. When combined with other measures of fitness, EE and CHO utilization during cycling can be estimated accurately. These models can be applied in running and kayaking when used with a calibration adjustment.
... The 'recoverlow' strategy involves restricting CHO intake after a single exercise session; this approach can affect both muscle and liver glycogen recovery depending on the exercise intensity, the duration of the CHO restriction, and the pre-exercise breakfast intake. Lastly, 'twice-a-day training' is a strategy that involves a training session to reduce muscle glycogen, followed by several hours of reduced CHO intake, and then a second exercise session on the same day that commences with reduced muscle glycogen [8][9][10]. ...
Article
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Background The growing interest in how exercise and carbohydrate (CHO) restriction may modify molecular responses that promote endurance adaptations has led to many interesting controversies. Objective We conducted a systematic review and a meta-analysis regarding the effect of low-carbohydrate availability (LOW) pre-, during, or post-exercise, on the mRNA content of commonly measured genes involved in mitochondrial biogenesis (PGC-1α, TFAM mRNA) and metabolism (PDK4, UCP3 and GLUT4 mRNA), and on muscle glycogen levels, compared with a high-CHO (CON) condition. Methods MEDLINE, Scopus, and Web of Science databases were searched following the PRISMA 2020 guidelines (with an end date of November 2023). In total, 19 randomized-controlled studies were considered for inclusion. We evaluated the methodological quality of all studies using the Cochrane Risk of Bias tool for randomized clinical studies. A meta-analysis was performed using a random effects model to calculate the standardized mean difference (SMD), estimated by Hedges’ g, and 95% confidence intervals (CIs). Results The LOW condition was associated with an increased mRNA content of several genes during the early recovery period post-exercise, such as PDK4 (SMD 1.61; 95% CI 0.80–2.42), GLUT4 (SMD 1.38; 95% CI 0.46–2.30), and UCP3 (SMD 2.05; 95% CI 0.40–3.69). However, overall, there was no significant effect on the mRNA content of PGC-1α or TFAM. Finally, CHO restriction and exercise significantly reduced muscle glycogen levels (SMD 3.69; 95% CI 2.82–5.09). A meta-analysis of subgroups from studies with a difference in muscle glycogen concentration of > 200 mmol kg dw⁻¹ between the LOW and CON conditions showed an increase in exercise-induced PGC-1α mRNA (SMD 2.08; 95% CI 0.64–3.52; p = 0.005; I² = 75%) and a greater effect in PDK4 and GLUT4 mRNA. Conclusion The meta-analysis results show that CHO restriction was associated with an increase in the exercise-induced mRNA content of PDK4, UCP3, and GLUT4, but not the exercise-induced mRNA content of PGC-1ɑ and TFAM. However, when there were substantial differences in glycogen depletion between CON and LOW CHO conditions (> 200 mmol kg dw⁻¹), there was a greater effect of CHO restriction on the exercise-induced mRNA content of metabolic genes, and an increase in exercise-induced PGC-1α mRNA.
... Sherman et al. 12 relacionaram a depleção do glicogênio muscular com fadiga em exercícios prolongados. Hawley et al. 13 e Burke et al. 14 concluíram que nos exercícios prolongados submáximos (75% do VO 2max ) maior que 90 minutos, o glicogênio muscular minimiza a fadiga muscular. ...
Article
Introdução: Em atividades físicas prolongadas a reposição hídrica e o conteúdo de glicogênio muscular são fatores limitantes em corredores de maratonas. O carregamento de carboidrato (CHO) nos dias anteriores à competição de resistência é um método comumente empregado para otimizar os estoques de glicogênio muscular e o desempenho no exercício. Uma vez que cada grama de glicogênio muscular liga-se a ≈2,7 a 4 gramas de água, a retenção hídrica pode ocorrer durante dietas de carregamento de carboidrato. Objetivo: Avaliar diferenças entre as estratégias de carregamento de carboidratos (Bergström e Sherman) no teor de água intracelular (AIC) ou água extracelular (AEC). Métodos: Vinte e três corredores foram alocados aleatoriamente para duas intervenções (Bergström e Sherman) num delineamento em “crossover”. Os participantes foram submetidos a uma avaliação inicial antes dos 3 dias de depleção de glicogênio, seguidos por 3 dias de carga de carboidratos com tempo de “washout” de 30 dias consistindo em dieta e treinamento normais. Utilizou-se a bioimpedância multifrequencial (BIS) para avaliar AIC e AEC na Etapa Inicial, Pós-depleção e Pós-CHO para determinar quaisquer diferenças entre os protocolos de Bersgstrom e Sherman. Também foram obtidas coletas de sangue para avaliar o potássio. Foram determinadas associações entre AIC, AEC e glicogênio muscular. Resultados: Não houve diferenças no conteúdo de AIC ou AEC entre as duas intervenções em qualquer momento. Houve um efeito do tempo para AIC, com aumento da etapa Pós-depleção para Pós-CHO sem qualquer diferença entre as intervenções. O potássio plasmático diminuiu entre a Linha de base e Pós-depleção em ambas condições. Não houve diferença no conteúdo de glicogênio muscular entre intervenções ou momentos. Conclusão: Não houve diferenças no conteúdo de AIC e AEC entre as intervenções de Bergström e Sherman em qualquer momento. Nível de Evidência I; Testes de Critérios Diagnósticos Desenvolvidos Anteriormente.
... Sherman et al. 12 showed an association between muscle glycogen depletion and fatigue during prolonged exercise. Hawley et al. 13 and Burke et al. 14 concluded that, during prolonged submaximal exercises (75% of VO 2max ) of longer than 90 minutes, muscle glycogen minimized muscle fatigue. ...
Article
Introduction: In prolonged physical activities, water replacement and muscle glycogen content are limiting factors in marathon runners. Carbohydrate-loading (CHO) in the days prior to endurance competition is a commonly employed method to optimise muscle glycogen stores and optimise exercise performance. Since each gram of muscle glycogen binds ~2.7-4 grams of water, water retention may occur during carbohydrateloading diets. Objective: To evaluate differences between CHO loading strategies (Bergström and Sherman) on intracellular (ICW) and extracellular (ECW) water content. Methods: Twenty-three runners were randomly allocated to two interventions (Bergström and Sherman) in a crossover design. Participants underwent a baseline evaluation before 3 days of glycogen depletion followed by 3 days of carbohydrate loading with a washout of 30 days consisting of normal diet and training. Multifrequency bioimpedance (BIS) was used to assess ICW and ECW at Baseline, Post-depletion and Post-CHO to determine any differences between Bergström and Sherman protocols. Blood samples were also obtained to assess potassium levels. Associations between ICW and ECW and muscle glycogen were determined. Results: There were no differences in ICW or ECW content between the two interventions at any moment. There was an effect of time for ICW, with an increase from Post-depletion to Post-CHO without any difference between interventions. Plasma potassium decreased from Baseline to Postdepletion in both conditions. There was no difference in muscle glycogen content between interventions or moments. Conclusion: There were no differences in ICW and ECW content between the Bergström and Sherman interventions at any moment. Level of Evidence I; Tests of Previously Developed Diagnostic Criteria.
... Anderson et al. reported in their study that the constant availability of carbohydrates throughout the training days reduced activity in the molecular pathways that regulate exercise adaptation [3]. Although various forms of carbohydrate periodization to improve athletes" performance have been proposed [14,15], they have not been tested in professional soccer players [1]. ...
Article
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Background: Carbohydrate loading is an established sports nutrition strategy for endur-16 ance exercise performance. We tested if carbohydrate loading could improve the performance of 17 elite soccer players under ecologically valid circumstances using Global Positioning System (GPS) data. Methods: Twenty-two adult Iran Premier league soccer players were divided into a carbohydrate-loading group (CLG) and Control group (CG). The carbohydrate loading group restricted carbohydrate intake for three days to 1.5 g/kg/d while increasing exercise intensity. From days four to seven, exercise intensity was decreased and carbohydrate intake was considerably increased up to 7.5 g/kg/d on the day of the match, during which performance was analyzed using GPS data. The control group performed the same exercise training but maintained their habitual carbohydrate intake of 5-6 g/kg/d. The data were analyzed using a univariate ANCOVA with baseline data from a pre-intervention match as the control variable. Results: The carbohydrate loading team scored significantly higher on running distance, maximum speed and the number of top and repeated sprints; the carbohydrate loading group scored significantly lower on player load, metabolic power and running imbalance compared to the control team during their match. Conclusions: Our findings suggest carbohydrate loading enabled elite soccer players to achieve greater running outputs with greater metabolic efficiency and lower fatigue compared to their habitual diets. ARTICLE HISTORY
... Current understanding, however, perceives manipulation of carbohydrate availability as the primary means of periodizing sports nutrition (Stellingwerff, Morton & Burke, 2019in support of training periodization there has been an emergence around the concept of nutritional periodization. Within athletics (track and field; Impey et al., 2018;Burke et al., 2018). Therefore, the periodization of sports nutrition is a strictly planned process in which the primary task of sports nutrition is to support the athlete's training outcomes (Jeukendrup, 2017). ...
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Both training and dietary practices used by athletes greatly vary. Current sports nutrition guidelines promote dietary manipulation of energy-yielding nutrients specific to the period of training. The study explores the ad libitum nutrition practices of four healthy adult recreational athletes during a 2-week cycling training camp (~100 km·d-1, ~240 min·d-1) with particular attention to the current sports nutrition recommendations. Based on evidence-based guidelines, peri-exercise carbohydrate (CHO) and protein (PRO) intake periodization cut-off levels were set for athletes. Training days were categorized as hard (HARD, two training units/day), middle (MID, one training unit/day), and easy (LOW, no training). Fourteen-day diet records were used and analyzed by nutritional software for energy intake (EI), carbohydrate (CHO), and protein (PRO) intake. Relative daily EI of 78.6±4.5, 73.3±6.4, 75.4±8.2 kcal·kg·d-1, and CHO 8.9±0.8, 7.8±1.0, 8.2±1.5 g·kg1 intakes were not different in HARD, MID and LOW days, respectively. The mean daily EI was 1.3× higher than the predicted total daily energy expenditure, irrespective of the training day category, resulting in ~500 kcal·d-1 energy surplus. In the 2h post-exercise period, PRO intake exceeded the current recommendations 4.6-fold, and CHO intake was significantly lower after a second training session on HARD days (0.7 g·kg·h-1) than a recommendation (1.2 g·kg·h-1). Mean in-exercise CHO intake (~11.5 g·h-1) was significantly under the moderate 30 g·h-1 recommendation. In conclusion, the dietary behaviours of recreational athletes are not consistent with current sports nutrition periodization guidelines. Energy intake throughout the training camp led to positive energy balance being highest on non-training days. Daily or during and post-exercise CHO and PRO intakes were not adjusted to the training sessions' volume, intensity, or duration.
... (i.e., glycogen-depleting session of training is followed by overnight carbohydrate (CHO) restriction and a moderate-intensity session the subsequent morning), "fasted exercise" (i.e., performing endurance exercise in a fasted state, after an overnight fast and without CHO intake during session), or "twice-a-day training" (i.e., two sessions on the same day; the second is commenced with reduced muscle glycogen) [7]. Some studies found improvements in performance after the application of these nutritional protocols [8,9]. ...
Article
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There is a growing interest in studies involving carbohydrate (CHO) manipulation and subsequent adaptations to endurance training. This study aimed to analyze whether a periodized carbohydrate feeding strategy based on a daily training session has any advantages compared to a high-carbohydrate diet in well-trained cyclists. Seventeen trained cyclists (VO2peak = 70.8 ± 6.5 mL·kg−1·min−1) were divided into two groups, a periodized (PCHO) group and a high-carbohydrate (HCHO) group. Both groups performed the same training sessions for five weeks. In the PCHO group, 13 training sessions were performed with low carbohydrate availability. In the HCHO group, all sessions were completed following previous carbohydrate intake to ensure high pre-exercise glycogen levels. In both groups, there was an increase in the maximal lactate steady state (MLSS) (PCHO: 244.1 ± 29.9 W to 253.2 ± 28.4 W; p = 0.008; HCHO: 235.8 ± 21.4 W to 246.9 ± 16.7 W; p = 0.012) but not in the time to exhaustion at MLSS intensity. Both groups increased the percentage of muscle mass (PCHO: p = 0.021; HCHO: p = 0.042) and decreased the percent body fat (PCHO: p = 0.021; HCHO: p = 0.012). We found no differences in carbohydrate or lipid oxidation, heart rate, and post-exercise lactate concentration. Periodizing the CHO intake in well-trained cyclists during a 5-week intervention did not elicit superior results to an energy intake-matched high-carbohydrate diet in any of the measured outcomes.
... Sherman et al. 12 linked muscle glycogen depletion with fatigue during prolonged exercise. Hawley et al. 13 and Burke et al. 14 concluded that in prolonged submaximal exercise (75% of VO 2max ) over 90 minutes, muscle glycogen minimizes muscle fatigue. ...
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Introduction In prolonged physical activities, water replacement and muscle glycogen content are limiting factors in marathon runners. Carbohydrate-loading (CHO) in the days prior to endurance competition is a commonly employed method to optimise muscle glycogen stores and optimise exercise performance. Since each gram of muscle glycogen binds ∼2.7-4 grams of water, water retention may occur during carbohydrate-loading diets. Objective To evaluate differences between CHO loading strategies (Bergström and Sherman) on intracellular (ICW) and extracellular (ECW) water content. Methods Twenty-three runners were randomly allocated to two interventions (Bergström and Sherman) in a crossover design. Participants underwent a baseline evaluation before 3 days of glycogen depletion followed by 3 days of carbohydrate loading with a washout of 30 days consisting of normal diet and training. Multifrequency bioimpedance (BIS) was used to assess ICW and ECW at Baseline, Post-depletion and Post-CHO to determine any differences between Bergström and Sherman protocols. Blood samples were also obtained to assess potassium levels. Associations between ICW and ECW and muscle glycogen were determined. Results There were no differences in ICW or ECW content between the two interventions at any moment. There was an effect of time for ICW, with an increase from Post-depletion to Post-CHO without any difference between interventions. Plasma potassium decreased from Baseline to Post-depletion in both conditions. There was no difference in muscle glycogen content between interventions or moments. Conclusion There were no differences in ICW and ECW content between the Bergström and Sherman interventions at any moment. Level of Evidence I; Tests of Previously Developed Diagnostic Criteria. Descriptors: Body Composition; Glycogen; Fluid Therapy; Exercise; Diet
... Sherman et al. 12 relacionaram a depleção do glicogênio muscular com fadiga em exercícios prolongados. Hawley et al. 13 e Burke et al. 14 concluíram que nos exercícios prolongados submáximos (75% do VO 2max ) maior que 90 minutos, o glicogênio muscular minimiza a fadiga muscular. ...
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Introduction In prolonged physical activities, water replacement and muscle glycogen content are limiting factors in marathon runners. Carbohydrate-loading (CHO) in the days prior to endurance competition is a commonly employed method to optimise muscle glycogen stores and optimise exercise performance. Since each gram of muscle glycogen binds ∼2.7-4 grams of water, water retention may occur during carbohydrate-loading diets. Objective To evaluate differences between CHO loading strategies (Bergström and Sherman) on intracellular (ICW) and extracellular (ECW) water content. Methods Twenty-three runners were randomly allocated to two interventions (Bergström and Sherman) in a crossover design. Participants underwent a baseline evaluation before 3 days of glycogen depletion followed by 3 days of carbohydrate loading with a washout of 30 days consisting of normal diet and training. Multifrequency bioimpedance (BIS) was used to assess ICW and ECW at Baseline, Post-depletion and Post-CHO to determine any differences between Bergström and Sherman protocols. Blood samples were also obtained to assess potassium levels. Associations between ICW and ECW and muscle glycogen were determined. Results There were no differences in ICW or ECW content between the two interventions at any moment. There was an effect of time for ICW, with an increase from Post-depletion to Post-CHO without any difference between interventions. Plasma potassium decreased from Baseline to Post-depletion in both conditions. There was no difference in muscle glycogen content between interventions or moments. Conclusion There were no differences in ICW and ECW content between the Bergström and Sherman interventions at any moment. Level of Evidence I; Tests of Previously Developed Diagnostic Criteria. Descriptors: Body Composition; Glycogen; Fluid Therapy; Exercise; Diet
... RED-S has gained traction both in clinical practice and recent literature (Cabre et al., 2022), with an emphasis on low energy availability prior to symptom manifestation or injury occurrence (Melin et al., 2014;Wasserfurth et al., 2020). Although a more holistic approach to training has been recognized Mujika et al., 2018;Stellingwerff et al., 2018;Ackerman et al., 2019), limited approaches exist to aid in the early detection of low energy availability from a pre-season perspective (Heikura et al., 2022). Similar to training phases or blocks in a yearly periodization plan, there are different dietary phases that can be to address the "transition phase" (pre-competition and competition). ...
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Background: Diet monitoring is part of an athlete’s health and performance assessment, and adequate nutrition is known to be a method that can positively influence the reduction in exercise-induced injury. However, the concept of nutritional preparedness as a screening tool to identify low energy availability for the competitive season is not mainstream practise. Objectives: Our pilot study investigated three aims: 1) changes to nutritional status from the pre-competition phase to the competition phase, 2) living status impact on athlete’s food accessibility, and 3) whether nutritional preparedness in the pre-competition phase influenced the potential for low energy availability during the competition phase. Methods: Female volleyball athletes (N=21, 19-22 yrs., 80% lived off campus) were recruited from 3 universities (Ambrose, Calgary, New Brunswick- Saint John) through social media sites, and word of mouth. Two cross-sectional questionnaires (questions derived from the Short Food Frequency-Q, LEAF-Q, and RED-S screening tool-Q) were administered prior to and during the competitive season. Results: The nutritional assessment score significantly decreased from the pre-competition to competition phase, respectively (n=20, 26.11 ± 4.25; n=12, 20.64 ± 4.74; p=0.022). Many athletes (6/12) reported an injury during the competitive season with an average time loss from sport of 8-14 days. Conclusions: These findings suggest that collegiate female volleyball athletes have a potential for low energy availability, regardless of living status. Future research should build on the nutritional preparedness concept as a method of screening for low energy availability and the influence on injuries sustained during the competition phase.
... Recent reviews have discussed dietary (Mohr et al. 2020) and supplement intake (Donati Zeppa et al. 2019), in relation to the GM balance in athletes. The intake of functional foods containing high-energy sources of CHOs (e.g., glucose, fructose, sucrose, and dextrose) before and during exercise may reduce fatigue, improve performance, and promote water reabsorption and maintenance of euhydration (Clark and Mach 2016;Burke et al. 2018). However, excess glucose or fructose load, and the fructose/glucose ratio affect GM fermentation and cause GI distress (Erickson et al. 2017). ...
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To improve performance and recovery faster, athletes are advised to eat more often than usual and consume higher doses of simple carbohydrates, during and after exercise. Sports energetic supplements contain food additives, such as artificial sweeteners, emulsifiers, acidity regulators, preservatives, and salts, which could be harmful to the gut microbiota and impair the intestinal barrier function. The intestinal barrier plays a critical function in bidirectionally regulation of the selective transfer of nutrients, water, and electrolytes, while preventing at the same time, the entrance of harmful substances (selective permeability). The gut microbiota helps to the host to regulate intestinal homeostasis through metabolic, protective, and immune functions. Globally, the gut health is essential to maintain systemic homeostasis in athletes, and to ensure proper digestion, metabolization, and substrate absorption. Gastrointestinal complaints are an important cause of underperformance and dropout during endurance events. These complications are directly related to the loss of gut equilibrium, mainly linked to microbiota dysbiosis and leaky gut. In summary, athletes must be cautious with the elevated intake of ultra-processed foods and specifically those contained on sports nutrition supplements. This review points out the specific nutritional interventions that should be implemented and/or discontinued depending on individual gut functionality.
... Anderson et al. reported in their study that the constant availability of carbohydrates throughout the training days reduced activity in the molecular pathways that regulate exercise adaptation [3]. Although various forms of carbohydrate periodization to improve athletes" performance have been proposed [14,15], they have not been tested in professional soccer players [1]. ...
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Background Carbohydrate loading is an established sports nutrition strategy for endur- 16 ance exercise performance. We tested if carbohydrate loading could improve the performance of 17 elite soccer players under ecologically valid circumstances using Global Positioning System (GPS) data. Methods Twenty-two adult Iran Premier league soccer players were divided into a carbohydrate-loading group (CLG) and Control group (CG). The carbohydrate loading group restricted carbohydrate intake for three days to 1.5 g/kg/d while increasing exercise intensity. From days four to seven, exercise intensity was decreased and carbohydrate intake was considerably increased up to 7.5 g/kg/d on the day of the match, during which performance was analyzed using GPS data. The control group performed the same exercise training but maintained their habitual carbohydrate intake of 5–6 g/kg/d. The data were analyzed using a univariate ANCOVA with baseline data from a pre-intervention match as the control variable. Results The carbohydrate loading team scored significantly higher on running distance, maximum speed and the number of top and repeated sprints; the carbohydrate loading group scored significantly lower on player load, metabolic power and running imbalance compared to the control team during their match. Conclusions Our findings suggest carbohydrate loading enabled elite soccer players to achieve greater running outputs with greater metabolic efficiency and lower fatigue compared to their habitual diets.
... Knowledge and practice around the ideal training diet for endurance athletes has evolved from universally high carbohydrate (CHO) intakes to consistent high CHO (HCHO) availability (matching CHO intake to the acute fuel demands of each training session) and, more recently, to periodized CHO (PCHO) availability (high availability for training quality and low availability to increase metabolic adaptation, according to the characteristics of each session). 1 However, the last decade has seen renewed interest in ketogenic, low-CHO, high-fat (LCHF) diets as an alternative strategy to enhance endurance performance via increased reliance on a more abundant muscle fuel source. 2,3 Our investigation of the effect of these different approaches to the training diet on exercise metabolism and performance in elite endurance athletes found that although the LCHF diet achieved a doubling of fat oxidation, it resulted in an impairment of real-world sport performance compared to diets providing HCHO or PCHO availability. ...
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Purpose: To examine the effects of a high-carbohydrate diet (HCHO), periodized-carbohydrate (CHO) diet (PCHO), and ketogenic low-CHO high-fat diet (LCHF) on training capacity. Methods: Elite male racewalkers completed 3 weeks of periodic training while adhering to their dietary intervention. Twenty-nine data sets were collected from 21 athletes. Each week, 6 mandatory training sessions were completed, with additional sessions performed at the athlete's discretion. Mandatory sessions included an interval session (10 × 1-km efforts on a 6-min cycle), tempo session (14 km with a 450-m elevation gain), 2 long walks (25-40 km), and 2 easy walks (8-12 km) where "sleep-low" and "train-low" dietary strategies were employed for PCHO. Racewalking speed, heart rate, rating of perceived exhaustion, and blood metabolites were collected around key sessions. Results: LCHF covered less total distance than HCHO and PCHO (P < .001); however, no differences in training load between groups were evident (P = .285). During the interval sessions, walking speed was slower in LCHF (P = .001), equating to a 2.8% and 5.6% faster speed in HCHO and PCHO, respectively. LCHF was also 3.2% slower in completing the tempo session than HCHO and PCHO (P = .001). Heart rate was higher (P = .002) and lactate concentrations were lower (P < .001) in LCHF compared to other groups, despite slower walking speeds during the interval session. No between-groups differences in rating of perceived exhaustion were evident (P = .077). Conclusion: Athletes adhering to an LCHF diet showed impaired training capacity relative to their high-CHO-supported counterparts, completing lower training volumes at slower speeds, with higher heart rates.
... It is well documented that carbohydrate availability during exercise is ergogenic as CHO feeding can help maintain plasma glucose and prevent hypoglycemia, spare hepatic glycogen, and delay muscle glycogen depletion [195][196][197][198]. However, in women, estrogen and muscle metabolic effects directly reduce carbohydrate utilization due to a marked hepatic glycogen sparing effect and insulin-mediated storage, thus indirectly shifting substrate utilization toward lipids across low to moderate intensity exercise. ...
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Based on a comprehensive review and critical analysis of the literature regarding the nutritional concerns of female athletes, conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society: 1. Female athletes have unique and unpredictable hormone profiles, which influence their physiology and nutritional needs across their lifespan. To understand how perturbations in these hormones affect the individual, we recommend that female athletes of reproductive age should track their hormonal status (natural, hormone driven) against training and recovery to determine their individual patterns and needs and peri and post-menopausal athletes should track against training and recovery metrics to determine the individuals' unique patterns. 2. The primary nutritional consideration for all athletes, and in particular, female athletes, should be achieving adequate energy intake to meet their energy requirements and to achieve an optimal energy availability (EA); with a focus on the timing of meals in relation to exercise to improve training adaptations, performance, and athlete health. 3. Significant sex differences and sex hormone influences on carbohydrate and lipid metabolism are apparent, therefore we recommend first ensuring athletes meet their carbohydrate needs across all phases of the menstrual cycle. Secondly, tailoring carbohydrate intake to hormonal status with an emphasis on greater carbohydrate intake and availability during the active pill weeks of oral contraceptive users and during the luteal phase of the menstrual cycle where there is a greater effect of sex hormone suppression on gluconogenesis output during exercise. 4. Based upon the limited research available, we recommend that pre-menopausal, eumenorrheic, and oral contraceptives using female athletes should aim to consume a source of high-quality protein as close to beginning and/or after completion of exercise as possible to reduce exercise-induced amino acid oxidative losses and initiate muscle protein remodeling and repair at a dose of 0.32-0.38 g·kg-1. For eumenorrheic women, ingestion during the luteal phase should aim for the upper end of the range due to the catabolic actions of progesterone and greater need for amino acids. 5. Close to the beginning and/or after completion of exercise, peri- and post-menopausal athletes should aim for a bolus of high EAA-containing (~10 g) intact protein sources or supplements to overcome anabolic resistance. 6. Daily protein intake should fall within the mid- to upper ranges of current sport nutrition guidelines (1.4-2.2 g·kg-1·day-1) for women at all stages of menstrual function (pre-, peri-, post-menopausal, and contraceptive users) with protein doses evenly distributed, every 3-4 h, across the day. Eumenorrheic athletes in the luteal phase and peri/post-menopausal athletes, regardless of sport, should aim for the upper end of the range. 7. Female sex hormones affect fluid dynamics and electrolyte handling. A greater predisposition to hyponatremia occurs in times of elevated progesterone, and in menopausal women, who are slower to excrete water. Additionally, females have less absolute and relative fluid available to lose via sweating than males, making the physiological consequences of fluid loss more severe, particularly in the luteal phase. 8. Evidence for sex-specific supplementation is lacking due to the paucity of female-specific research and any differential effects in females. Caffeine, iron, and creatine have the most evidence for use in females. Both iron and creatine are highly efficacious for female athletes. Creatine supplementation of 3 to 5 g per day is recommended for the mechanistic support of creatine supplementation with regard to muscle protein kinetics, growth factors, satellite cells, myogenic transcription factors, glycogen and calcium regulation, oxidative stress, and inflammation. Post-menopausal females benefit from bone health, mental health, and skeletal muscle size and function when consuming higher doses of creatine (0.3 g·kg-1·d-1). 9. To foster and promote high-quality research investigations involving female athletes, researchers are first encouraged to stop excluding females unless the primary endpoints are directly influenced by sex-specific mechanisms. In all investigative scenarios, researchers across the globe are encouraged to inquire and report upon more detailed information surrounding the athlete's hormonal status, including menstrual status (days since menses, length of period, duration of cycle, etc.) and/or hormonal contraceptive details and/or menopausal status.
... Sports nutrition guidelines recommend that athletes 'fuel for the work required' (12,13) , with periodized nutrition plans individually tailored for athletes' training, competition and physique goals (14) . Fuelling recommendations use a food-first approach, recognising that a carefully planned whole-food diet provides appropriate fuel and hydration for performance and recovery (15,16) . ...
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Sports foods are convenient alternatives to everyday foods to fuel performance. Strong scientific evidence supports their use; however, commercial sports foods are classified by the NOVA system as ultra-processed foods (UPF). Consumption of UPF has been associated with poor mental and physical health, but little is known about athletes' consumption of and attitudes toward sports foods as a source of UPF. The aim of this cross-sectional study was to assess Australian athletes' intake of and attitudes toward sports foods and UPF. Adult athletes were recruited to complete an anonymous online survey via social media between October 2021 and February 2022. Data were analysed using descriptive statistics, and Pearson's chi-square test was used to assess potential relationships between categorical demographic variables and consumption of sports foods. One hundred forty Australian adults participating in recreational (n=55), local/regional (n=52), state (n=11), national (n=14), or international (n=9) sports completed the survey. Ninety-five per cent reported consuming sports foods within the past 12 months. Participants consumed sports drinks most commonly (73%) and isolated protein supplements most frequently (40% at least once per week). Participants reported everyday foods to be more affordable, taste better, present less risk of banned substances, but less convenient, and greater risk of spoilage. Half (51%) of participants reported concern about health effects of UPF. Participants reported regular UPF consumption despite taste and cost-related preferences for everyday foods and health concerns regarding UPF intake. Athletes may need support to identify and access safe, affordable, convenient, minimally processed alternatives to sports foods.
... Storage of glycogen is associated with a gain in body mass, which may be detrimental to performance in weightbearing sports. 1 Thus, manipulation of pre-exercise skeletal muscle glycogen content could be a strategy to optimize body mass prior to competition, provided that glycogen depletion does not become limiting for performance. The importance of muscle glycogen availability for performance during long-term (>1 h) exercise at moderate to high intensities is well established and has been confirmed in numerous studies by different research groups. ...
Article
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Performance in short-duration sports is highly dependent on muscle glycogen, but the total degradation is only moderate and considering the water-binding property of glycogen, unnecessary storing of glycogen may cause an unfavorable increase in body mass. To investigate this, we determined the effect of manipulating dietary carbohydrates (CHO) on muscle glycogen content, body mass and short-term exercise performance. In a cross-over design twenty-two men completed two maximal cycle tests of either 1-min (n = 10) or 15-min (n = 12) duration with different pre-exercise muscle glycogen levels. Glycogen manipulation was initiated three days prior to the tests by exercise-induced glycogen-depletion followed by ingestion of a moderate (M-CHO) or high (H-CHO) CHO-diet. Subjects were weighed before each test, and muscle glycogen content was determined in biopsies from m. vastus lateralis before and after each test. Pre-exercise muscle glycogen content was lower following M-CHO than H-CHO (367 mmol · kg-1 DW vs. 525 mmol · kg-1 DW, P < 0.00001), accompanied by a 0.7 kg lower body mass (P < 0.00001). No differences were observed in performance between diets in neither the 1-min (P = 0.33) nor the 15-min (P = 0.99) test. In conclusion, pre-exercise muscle glycogen content and body mass was lower after ingesting moderate compared with high amounts of CHO, while short-term exercise performance was unaffected. This demonstrates that adjusting pre-exercise glycogen levels to the requirements of competition may provide an attractive weight management strategy in weight-bearing sports, particularly in athletes with high resting glycogen levels.
... However, it was only at the Montreal Olympic Games in 1976 that an appreciation of the importance of dietary carbohydrates among athletes and coaches started to emerge [3]. Together with other advances made towards improving athletic performance, such as improved equipment and training methodology, researchers continued to study carbohydrate metabolism to better understand the mechanisms of how dietary carbohydrates improve performance, promote recovery and/or prevent fatigue, as well as researching strategies to optimize carbohydrate availability in athletes [7][8][9][10]. Over this period, understanding of the actions of dietary carbohydrates on exercise metabolism and performance has increased substantially and, in concert, nutritional recommendations for athletes have developed and continue to evolve to reflect contemporary knowledge and practice. ...
Article
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The importance of carbohydrate as a fuel source for exercise and athletic performance is well established. Equally well developed are dietary carbohydrate intake guidelines for endurance athletes seeking to optimize their performance. This narrative review provides a contemporary perspective on research into the role of, and application of, carbohydrate in the diet of endurance athletes. The review discusses how recommendations could become increasingly refined and what future research would further our understanding of how to optimize dietary carbohydrate intake to positively impact endurance performance. High carbohydrate availability for prolonged intense exercise and competition performance remains a priority. Recent advances have been made on the recommended type and quantity of carbohydrates to be ingested before, during and after intense exercise bouts. Whilst reducing carbohydrate availability around selected exercise bouts to augment metabolic adaptations to training is now widely recommended, a contemporary view of the so-called train-low approach based on the totality of the current evidence suggests limited utility for enhancing performance benefits from training. Nonetheless, such studies have focused importance on periodizing carbohydrate intake based on, among other factors, the goal and demand of training or competition. This calls for a much more personalized approach to carbohydrate recommendations that could be further supported through future research and technological innovation (e.g., continuous glucose monitoring). Despite more than a century of investigations into carbohydrate nutrition, exercise metabolism and endurance performance, there are numerous new important discoveries, both from an applied and mechanistic perspective, on the horizon.
... However, the optimum diet and exercise regime remains elusive, and diet and exercise interventions often have highly variable outcomes between individuals. This is evident in sports science, where defined diet strategies have been designed to optimise energy availability and complement athletic outcomes [3]. Yet, individual factors are the main determinant of athletic performance. ...
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Diet, exercise and the gut microbiome are all factors recognised to be significant contributors to cardiometabolic health. However, diet and exercise interventions to modify the gut microbiota to improve health are limited by poor understanding of the interactions between them. In this pilot study, we explored diet–exercise–microbiome dynamics in bodybuilders as they represent a distinctive group that typically employ well-defined dietary strategies and exercise regimes to alter their body composition. We performed longitudinal characterisation of diet, exercise, the faecal microbial community composition and serum metabolites in five bodybuilders during competition preparation and post-competition. All participants reduced fat mass while conserving lean mass during competition preparation, corresponding with dietary energy intake and exercise load, respectively. There was individual variability in food choices that aligned to individualised gut microbial community compositions throughout the study. However, there was a common shift from a high protein, low carbohydrate diet during pre-competition to a more macronutrient-balanced diet post-competition, which was associated with similar changes in the gut microbial diversity across participants. The circulating metabolite profiles also reflected individuality, but a subset of metabolites relating to lipid metabolism distinguished between pre- and post-competition. Changes in the gut microbiome and circulating metabolome were distinct for each individual, but showed common patterns. We conclude that further longitudinal studies will have greater potential than cross-sectional studies in informing personalisation of diet and exercise regimes to enhance exercise outcomes and improve health.
... Как правило, высокопрофессиональные спортсмены придерживаются специального рациона, особенно в тренировочный и предсоревновательный периоды. Нутритивный состав рационов варьирует в зависимости от вида и продолжительности тренировок для получения максимальной пользы от поступающих веществ и повышения эффективности тренировки, что лежит в основе производительности спортсменов [1][2][3]. ...
Article
It is known that under conditions of ultra-high physical activity and a specific diet, the state of the microbiota plays a significant role in maintaining the health, metabolic and energy status of athletes. The purpose of the study was to evaluate the composition of blood microbial markers in professional football players and physically active people and their correlation with diets in order to substantiate recommendations for their optimization. Material and methods. In a cross-sectional study a group of football players (n=24, 28±3 years old, body mass index - 22.5±1.0 kg/m2) who received a diet according to the training regimen, and a comparison group of physically active individuals (n=25, 34±5 years old, body mass index - 21.8±2.8 kg/m2) have been examined. The method of gas chromatography-mass spectrometry was used to analyze microbial markers of microbiome, mycobiome, virome and blood metabolome populations. Data on actual dietary intake were collected using food diaries for 3 days, followed by data processing with the Nutrium 2.13.0 nutritional computer program. For analysis, individual daily requirements for energy and macronutrients have been calculated based on the basal metabolic rate (according to the Mifflin-San Geor formula, taking into account anthropometric data), the coefficient of physical activity (groups IV and II, respectively). Results. The analysis of the athletes' diet, compared with individual requirements and with the recommendations of the International Society for Sports Nutrition (ISSN), revealed a lack of complex carbohydrates (5±1 instead of 6.1±0.3 g/kg body weight day), an excess of sugars (23±4 instead of <10% of kcal). These figures are significantly higher than the intake of similar nutrients in physically active people in the comparison group. In football players, compared with the comparison group, significant changes in microbial markers were found for Alcaligenes spp., Clostridium ramosum, Coryneform CDC-group XX, Staphylococcus epidermidis (p<0.001), known for their pro-inflammatory activity in the intestine, as well as for Lactobacillus spp. (p<0.001) performing a protective function. In addition, mycobiome markers were increased in athletes: Candida spp. (p<0.001), Aspergillus spp. (p<0.001), among which there are potential pathogens of mycoses. This was not observed in the comparison group. At the same time, an increase in the microbial markers of Alcaligenes spp., Coryneform CDC-group XX, Lactobacillus spp., Streptomyces spp., Candida spp. Micromycetes spp., containing campesterol in the cell wall, in football players positively correlated with a high calorie diet (p<0.001). A similar correlation of mycobiome markers (Micromycetes spp., containing sitosterol in the cell wall, ρ=0.346, p=0.015) was observed with an excess of easily digestible carbohydrates. Taking into account the data obtained, a correction of the diet have been proposed: increasing the consumption of carbohydrates to 7.3-7.5 g/kg of body weight/day by including bakery products from whole grain flour and cereals in the diet (up to 300-370 g/day), limiting simple sugars (up to 90-95 g/day). Conclusion. High physical activity leads to changes in the structure of blood microbial markers, including a shift towards an increase in potentially pathogenic fungi. Wherein, a predictive role is played by an imbalance of macronutrients in terms of quantitative and qualitative composition, an excess of simple sugars, and a lack of slowly digestible carbohydrates. To correct the diet, an additional inclusion in the diet of their main sources - products from cereals (cereals and bakery products) is proposed.
... We hypothesized that the LEA would be associated with small but transient changes in metabolism (i.e., substrate utilization) training capacity and well-being (e.g., mental stress, perceptions of recovery, and fatigue), while achieving a detectable change in body fat and body mass. However, acute restoration of CHO availability and EA for 24 h, as undertaken according to sports nutrition guidelines and included in the baseline and control group practices (25), would restore exercise capacity while maintaining body composition changes, allowing athletes to achieve similar (or even superior) benefits to race performance as athletes undertaking the same training program supported by HCHO. ...
... Though there was a small increase in carbohydrate intake with increasing EEE (Figure 3), the athletes consumed excess carbohydrate on 67% of "Rest" days and insufficient carbohydrate on 30% of "High" and 70% of "Very High" training volume days, relative to guideline recommendations (Thomas et al., 2016). Therefore, in the majority of the cases, our cohort failed to adequately match their carbohydrate intake to their training volume in accordance with contemporary nutrition guidelines (Burke, Hawley et al., 2018;Impey et al., 2018;Stellingwerff, 2018;Thomas et al., 2016). Collectively, these findings suggest that when elite endurance athletes are left to their own means in relation to their nutrition, they fail to ingest carbohydrates in line with current guidelines, resulting in lower energy (and carbohydrate) availability when undertaking a higher training volume. ...
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The physiological effects of low energy availability (EA) have been studied using a homogenous daily EA pattern in laboratory settings. However, whether this daily EA pattern represents those of free-living athletes and is therefore ecologically valid is unknown. To investigate this, we assessed daily exercise energy expenditure, energy intake and EA in 10 free-living elite male road cyclists (20 min Mean Maximal Power: 5.27 ± 0.25 W · kg⁻¹) during 7 consecutive days of late pre-season training. Energy intake was measured using the remote-food photography method and exercise energy expenditure estimated from cycling crank-based power-metres. Seven-day mean ± SD energy intake and exercise energy expenditure was 57.9 ± 10.4 and 38.4 ± 8.6 kcal · kg FFM⁻¹ · day⁻¹, respectively. EA was 19.5 ± 9.1 kcal · kg FFM⁻¹ · day⁻¹. Within-participants correlation between daily energy intake and exercise energy expenditure was .62 (95% CI: .43 – .75; P < .001), and .60 (95% CI: .41 – .74; P < .001) between carbohydrate intake and exercise energy expenditure. However, energy intake only partially compensated for exercise energy expenditure, increasing 210 kcal · day⁻¹ per 1000 kcal · day⁻¹ increase in expenditure. EA patterns displayed marked day-to-day fluctuation (range: −22 to 76 kcal · kg FFM⁻¹ · day⁻¹). The validity of research using homogenous low EA patterns therefore requires further investigation.
... For example, the strategic periodization of dietary CHO in order to commence exercise with low muscle glycogen (during 3-10 weeks of training) enhances mitochondrial enzyme activity and protein content (Hansen et al. 2005;Morton et al. 2009;Yeo et al. 2008) and whole body and intra-muscular lipid metabolism (Hulston et al. 2010) and in some instances improves exercise capacity (Hansen et al. 2005) and performance (Marquet et al. 2016a, b), though performance enhancing effects are not always evident (Yeo et al. 2008;Hulston et al. 2010;Burke et al. 2017;Gejl et al. 2017a, b;. As such, the train-low paradigm and wider CHO periodization strategies have subsequently gained increased recognition among athletic populations (Stellingwerff 2012;Burke et al. 2018;Impey et al. 2018). It should also be noted that some of the enhanced adaptations associated with "train-low" (at least in the twice per day training model) may be due to performing two consecutive training sessions in close proximity to one another, as opposed to the effects of low pre-exercise muscle glycogen per se (Andrade-Souza et al. 2020). ...
Chapter
Muscle glycogen is an important fuel source for contracting skeletal muscle, and it is well documented that exercise performance is impaired when the muscle’s stores of glycogen are exhausted. The role of carbohydrate (CHO) availability on exercise performance has been known for more than a century, while the specific role of muscle glycogen for muscle function has been known for half a century. Nonetheless, the precise cellular and molecular mechanisms by which glycogen availability regulates cell function and contractile-induced fatigue are unresolved. Alterations of pre-exercise muscle glycogen reserves by dietary and exercise manipulations or modifying the degree of dependency on endogenous glycogen during exercise have collectively established a close relationship between muscle glycogen and the resistance to fatigue. It is also apparent that glycogen availability regulates rates of muscle glycogenolysis and resynthesis, muscle glucose uptake, key steps in excitation-contraction coupling, and exercise-induced cell signaling regulating training adaptation. The present review provides both a historical and contemporary overview of the effects of exercise on muscle glycogen metabolism, addressing factors affecting glycogen use during exercise as well as the evolving concepts of how glycogen and glycolysis are integrated with cell function, skeletal muscle fatigue, and training adaptation.KeywordsGlycogenolysis, glycogen particleDietExerciseE-C coupling, fatigue, performance
... The ability to effectively oxidize fat for fuel, represented by a lower RER, is important for metabolic health [14] and long-duration exercise performance [15,16], and many athletes attempt to manipulate substrate oxidation during exercise as part of a periodized nutrition and training plan [17,18]. However, managing substrate oxidation during exercise is challenged by the influence of both modifiable The easily measured and easily modifiable factors related to exercise such as exercise duration and intensity, daily macronutrient intake, and pre-and peri-exercise carbohydrate intake, can only explain roughly one-third of the variation in RER during exercise. ...
Article
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Background: Multiple factors influence substrate oxidation during exercise including exercise duration and intensity, sex, and dietary intake before and during exercise. However, the relative influence and interaction between these factors is unclear. Objectives: Our aim was to investigate factors influencing the respiratory exchange ratio (RER) during continuous exercise and formulate multivariable regression models to determine which factors best explain RER during exercise, as well as their relative influence. Methods: Data were extracted from 434 studies reporting RER during continuous cycling exercise. General linear mixed-effect models were used to determine relationships between RER and factors purported to influence RER (e.g., exercise duration and intensity, muscle glycogen, dietary intake, age, and sex), and to examine which factors influenced RER, with standardized coefficients used to assess their relative influence. Results: The RER decreases with exercise duration, dietary fat intake, age, VO2max, and percentage of type I muscle fibers, and increases with dietary carbohydrate intake, exercise intensity, male sex, and carbohydrate intake before and during exercise. The modelling could explain up to 59% of the variation in RER, and a model using exclusively easily modified factors (exercise duration and intensity, and dietary intake before and during exercise) could only explain 36% of the variation in RER. Variables with the largest effect on RER were sex, dietary intake, and exercise duration. Among the diet-related factors, daily fat and carbohydrate intake have a larger influence than carbohydrate ingestion during exercise. Conclusion: Variability in RER during exercise cannot be fully accounted for by models incorporating a range of participant, diet, exercise, and physiological characteristics. To better understand what influences substrate oxidation during exercise further research is required on older subjects and females, and on other factors that could explain additional variability in RER.
... The control diets varied in the composition of macronutrients. We classified the control diets based on the proportion of CHO intake as normal (NCHO) when CHO ≈40%-59%, high (HCHO) when CHO ≧60%, and periodized (PCHO), which includes training sessions and periods of some days in a fasted state (Burke et al. 2018). Table 1. ...
Article
This systematic review with meta-analysis aimed to determine the effects of the ketogenic diet (KD) against carbohydrate (CHO)-rich diets on physical performance and body composition in trained individuals. The MEDLINE, EMBASE, CINAHL, SPORTDiscus, and The Cochrane Library were searched. Randomized and non-randomized controlled trials in athletes/trained adults were included. Meta-analytic models were carried out using Bayesian multilevel models. Eighteen studies were included providing estimates on cyclic exercise modes and strength one-maximum repetition (1-RM) performances and for total, fat, and free-fat masses. There were more favorable effects for CHO-rich than KD on time-trial performance (mode [95% credible interval]; −3.3% [−8.5%, 1.7%]), 1-RM (−5.7% [−14.9%, 2.6%]), and free-fat mass (−0.8 [−3.4, 1.9] kg); effects were more favorable to KD on total (−2.4 [−6.2, 1.8] kg) and fat mass losses (−2.4 [−5.4, 0.2] kg). Likely modifying effects on cyclic performance were the subject’s sex and VO2max, intervention and performance durations, and mode of exercise. The intervention duration and subjects’ sex were likely to modify effects on total body mass. KD can be a useful strategy for total and fat body losses, but a small negative effect on free-fat mass was observed. KD was not suitable for enhancing strength 1-RM or high-intensity cyclic performances.
... For the purposes of this review, the natural conclusion will be that since pre-exercise muscle glycogen content is determined by how much carbohydrate is ingested in the days prior to exercise (Figure 5), then a high-carbohydrate diet must always enhance performance in any exercise regardless of its duration or intensity. This is certainly the dietary advice that is now generally given [80][81][82][83][84][91][92][93][94]. ...
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The introduction of the needle muscle biopsy technique in the 1960s allowed muscle tissue to be sampled from exercising humans for the first time. The finding that muscle glycogen content reached low levels at exhaustion suggested that the metabolic cause of fatigue during prolonged exercise had been discovered. A special pre-exercise diet that maximized pre-exercise muscle glycogen storage also increased time to fatigue during prolonged exercise. The logical conclusion was that the athlete’s pre-exercise muscle glycogen content is the single most important acutely modifiable determinant of endurance capacity. Muscle biochemists proposed that skeletal muscle has an obligatory dependence on high rates of muscle glycogen/carbohydrate oxidation, especially during high intensity or prolonged exercise. Without this obligatory carbohydrate oxidation from muscle glycogen, optimum muscle metabolism cannot be sustained; fatigue develops and exercise performance is impaired. As plausible as this explanation may appear, it has never been proven. Here, I propose an alternate explanation. All the original studies overlooked one crucial finding, specifically that not only were muscle glycogen concentrations low at exhaustion in all trials, but hypoglycemia was also always present. Here, I provide the historical and modern evidence showing that the blood glucose concentration—reflecting the liver glycogen rather than the muscle glycogen content—is the homeostatically-regulated (protected) variable that drives the metabolic response to prolonged exercise. If this is so, nutritional interventions that enhance exercise performance, especially during prolonged exercise, will be those that assist the body in its efforts to maintain the blood glucose concentration within the normal range.
... Limited availability of endogenous carbohydrate (CHO) stores prompts athletes to attempt dietary interventions aimed at maximizing oxidation of endogenous fat substrate, at exercise intensities relevant to prolonged endurance and ultra-endurance competition (Phinney et al., 1983;Volek et al., 2016;Burke et al., 2020). It has been shown that acute or chronic low-carbohydrate high-fat (LCHF) dietary interventions [e.g., ≤1 gCHO/kg body mass (BM)/ day] increase whole-body fat oxidation during prolonged aerobic exercise in both highly trained and recreationally competitive athletes compared to typical carbohydrate dietary provisions (e.g., ~6 gCHO/kgBM/day; Burke et al., 2018;Russo et al., 2021b). Maximum fat oxidation (MFO) rate of 1.54 vs. 0.67 g/min during an incremental graded exercise test, and MFO occurring at a greater percentage of VȮ 2max (Fat max ; 70.3 vs. 54.9%), ...
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Using metadata from previously published research, this investigation sought to explore: (1) whole-body total carbohydrate and fat oxidation rates of endurance (e.g., half and full marathon) and ultra-endurance runners during an incremental exercise test to volitional exhaustion and steady-state exercise while consuming a mixed macronutrient diet and consuming carbohydrate during steady-state running and (2) feeding tolerance and glucose availability while consuming different carbohydrate regimes during steady-state running. Competitively trained male endurance and ultra-endurance runners (n = 28) consuming a balanced macronutrient diet (57 ± 6% carbohydrate, 21 ± 16% protein, and 22 ± 9% fat) performed an incremental exercise test to exhaustion and one of three 3 h steady-state running protocols involving a carbohydrate feeding regime (76–90 g/h). Indirect calorimetry was used to determine maximum fat oxidation (MFO) in the incremental exercise and carbohydrate and fat oxidation rates during steady-state running. Gastrointestinal symptoms (GIS), breath hydrogen (H2), and blood glucose responses were measured throughout the steady-state running protocols. Despite high variability between participants, high rates of MFO [mean (range): 0.66 (0.22–1.89) g/min], Fatmax [63 (40–94) % V̇O2max], and Fatmin [94 (77–100) % V̇O2max] were observed in the majority of participants in response to the incremental exercise test to volitional exhaustion. Whole-body total fat oxidation rate was 0.8 ± 0.3 g/min at the end of steady-state exercise, with 43% of participants presenting rates of ≥1.0 g/min, despite the state of hyperglycemia above resting homeostatic range [mean (95%CI): 6.9 (6.7–7.2) mmol/L]. In response to the carbohydrate feeding interventions of 90 g/h 2:1 glucose–fructose formulation, 38% of participants showed breath H2 responses indicative of carbohydrate malabsorption. Greater gastrointestinal symptom severity and feeding intolerance was observed with higher carbohydrate intakes (90 vs. 76 g/h) during steady-state exercise and was greatest when high exercise intensity was performed (i.e., performance test). Endurance and ultra-endurance runners can attain relatively high rates of whole-body fat oxidation during exercise in a post-prandial state and with carbohydrate provisions during exercise, despite consuming a mixed macronutrient diet. Higher carbohydrate intake during exercise may lead to greater gastrointestinal symptom severity and feeding intolerance.
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Background Carbohydrate restriction can alter substrate utilization and potentially impair endurance performance in female athletes. Caffeine intake may mitigate this performance decrements. Objectives The aim of this study was to test the hypothesis that maximal fat oxidation (MFO) rate would be enhanced in the carbohydrate (CHO) restricted state in trained females. Additionally, the impact of caffeine intake before exercise under conditions of low CHO availability was examined on time-trial performance. Methods By using a randomized, double-blinded, placebo-controlled, crossover design, 17 female endurance athletes completed 3 experimental blocks. Each block consisted of high-intensity-interval–training (HIT) in the evening, followed by a fat oxidation test to measure MFO rate and a 20-min time trial (20TT) performance the next morning. The females received standardized, isoenergetic diets with different timing of CHO intake: No CHO between exercise sessions without (FASTED) or with 300 mg caffeine (4.1–4.9 mg/kg body mass) (FASTED+CAFF) before morning exercise tests or CHO ingestion after HIT (FED). Results MFO rate was higher in FASTED+CAFF (0.57 ± 0.04 g/min) than that in FED (0.50 ± 0.04 g/min, P = 0.039) but not different from FASTED condition. Power output performed during the 20TT was higher after FASTED+CAFF (189 ± 9 W) than that after FASTED (+6.9%, P = 0.022) and FED (+4.2%, P = 0.054). Conclusions CHO restriction during recovery from HIT enhances MFO rate during subsequent exercise compared with the condition where CHOs were consumed during the recovery period, but the effect was only significant when CHO restriction was combined with caffeine supplementation before the MFO test. In addition, caffeine ingestion before exercise in the CHO-restricted state compensates for the decreased work capacity associated with the CHO-restricted state.
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This study investigated the effects of 14 days low energy availability (LEA) versus optimal energy availability (OEA) in endurance‐trained females on substrate utilization, insulin sensitivity, and skeletal muscle mitochondrial oxidative capacity; and the impact of metabolic changes on exercise performance. Twelve endurance‐trained females (V̇O2max 55.2 ± 5.1 mL × min⁻¹ × kg⁻¹) completed two 14‐day randomized, blinded, cross‐over, controlled dietary interventions: (1) OEA (51.9 ± 2.0 kcal × kg fat‐free mass (FFM)⁻¹ × day⁻¹) and (2) LEA (22.3 ± 1.5 kcal × kg FFM⁻¹ × day⁻¹), followed by 3 days OEA. Participants maintained their exercise training volume during both interventions (approx. 8 h × week⁻¹ at 79% heart rate max). Skeletal muscle mitochondrial respiratory capacity, glycogen, and maximal activity of CS, HAD, and PFK were unaltered with LEA. 20‐min time trial endurance performance was impaired by 7.8% (Δ −16.8 W, 95% CI: −23.3 to −10.4, p < .001) which persisted following 3 days refueling post‐LEA (p < .001). Fat utilization was increased post‐LEA as evidenced by: (1) 99.4% (p < .001) increase in resting plasma free fatty acids (FFA); (2) 270% (p = .007) larger reduction in FFA in response to acute exercise; and (3) 28.2% (p = .015) increase in resting fat oxidation which persisted during submaximal exercise (p < .001). These responses were reversed with 3 days refueling. Daily glucose control (via CGM), HOMA‐IR, HOMA‐β, were unaffected by LEA. Skeletal muscle O2 utilization and carbohydrate availability were not limiting factors for aerobic exercise capacity and performance; therefore, whether LEA per se affects aspects of training quality/recovery requires investigation.
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Low energy availability, particularly when problematic (i.e., prolonged and/or severe), has numerous negative consequences for health and sports performance as characterized in relative energy deficiency in sport. These consequences may be driven by disturbances in endocrine function, although scientific evidence clearly linking endocrine dysfunction to decreased sports performance and blunted or diminished training adaptations is limited. We describe how low energy availability-induced changes in sex hormones manifest as menstrual dysfunction and accompanying hormonal dysfunction in other endocrine axes that lead to adverse health outcomes, including negative bone health, impaired metabolic activity, undesired outcomes for body composition, altered immune response, problematic cardiovascular outcomes, iron deficiency, as well as impaired endurance performance and force production, all of which ultimately may influence athlete health and performance. Where identifiable menstrual dysfunction indicates hypothalamic-pituitary-ovarian axis dysfunction, concomitant disturbances in other hormonal axes and their impact on the athlete’s health and sports performance must be recognized as well. Given that the margin between podium positions and “losing” in competitive sports can be very small, several important questions regarding low energy availability, endocrinology, and the mechanisms behind impaired training adaptations and sports performance have yet to be explored.
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Introducción: La composición corporal es un indicador fundamental para definir el estado nutricional del corredor. Objetivo: El estudio tuvo como objetivo evaluar los efectos de la intervención de periodización nutricional en la composición corporal de corredores juveniles djiboutianos de élite en distancia media. Materiales y métodos: La muestra fue de 22 corredores masculinos, en edades comprendidas entre 16 y 18 años. Para la valoración, se diseñó un experimento constituido por 11 sujetos en el grupo control y 11 en el experimental. Como mediciones antropométricas se tomaron el peso, estatura y seis panículos adiposos para evaluar el porcentaje de grasa, índices de adiposidad, índice de masa corporal y el de sustancia corporal activa pues, para llevar el seguimiento de la intervención propuesta, se realizó una entrevista de recordatorio 24 horas de siete días. Resultados: Se diseñó una dieta periodizada, con la manipulación de los carbohidratos. La periodización nutricional con alta y baja ingesta de carbohidratos durante 12 semanas disminuyó significativamente (p< 0,05) el porcentaje de grasa, sin alterar el peso corporal ni el índice de sustancia corporal activa en los corredores djiboutianos de media distancia juveniles del grupo experimental. Conclusiones: Los resultados expuestos contribuyen a mejorar el control biomédico del entrenamiento en los corredores de élite juveniles de distancia media en Djibouti, ya que existían limitaciones de datos sobre su composición corporal y el efecto que pudiera tener la nutrición periodizada sobre esos indicadores Palabras clave : Periodización nutricional; Composición corporal; Corredores; Media distancia
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Purpose We examined iron absorption and its regulation during two common scenarios experienced by endurance athletes. Our aims were to: (i) compare the effects of preexercise versus postexercise iron intake on iron absorption; and (ii) compare the impact of training at altitude (1800 m) on iron absorption preexercise. Methods Male runners (n = 18) completed three exercise trials over a 5-wk period, each preceded by 24 h of standardized low-iron diets. First, athletes completed two 60-min treadmill running trials at 65% V̇O 2max at near sea-level (580 m). In a randomized order, preexercise and postexercise test meals labeled with 4 mg of ⁵⁷ Fe or ⁵⁸ Fe were consumed 30 min before or 30 min after exercise. Then, the same exercise trial was performed after living and training at altitude (~1800 m) for 7 d, with the labeled test meal consumed 30 min preexercise. We collected venous blood samples preexercise and postexercise for markers of iron status and regulation, and 14 d later to measure erythrocyte isotope incorporation. Results No differences in fractional iron absorption were evident when test meals were consumed preexercise (7.3% [4.4, 12.1]) or postexercise (6.2% [3.1, 12.5]) (n = 18; P = 0.058). Iron absorption preexercise was greater at altitude (18.4% [10.6, 32.0]) than at near sea-level (n = 17; P < 0.001) and hepcidin concentrations at altitude were lower at rest and 3 h postexercise compared with near sea level ( P < 0.001). Conclusions In an acute setting, preexercise and postexercise iron absorption is comparable if consumed within 30 min of exercise. Preexercise iron absorption increases 2.6-fold at altitude compared with near sea-level, likely due to the homeostatic response to provide iron for enhanced erythropoiesis and maintain iron stores.
Chapter
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Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM −1 ·day −1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM −1 ·day −1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM −1 ·day −1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.
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The aim of this audit was to assess the representation of female athletes, dietary control methods, and gold standard female methodology that underpins the current guidelines for chronic carbohydrate (CHO) intake strategies for athlete daily training diets. Using a standardized audit, 281 studies were identified that examined high versus moderate CHO, periodized CHO availability, and/or low CHO, high fat diets. There were 3,735 total participants across these studies with only ∼16% of participants being women. Few studies utilized a design that specifically considered females, with only 16 studies (∼6%) including a female-only cohort and six studies (∼2%) with a sex-based comparison in their statistical procedure, in comparison to the 217 studies (∼77%) including a male-only cohort. Most studies (∼72%) did not provide sufficient information to define the menstrual status of participants, and of the 18 studies that did, optimal methodology for control of ovarian hormones was only noted in one study. While ∼40% of male-only studies provided all food and beverages to participants, only ∼20% of studies with a female-specific design used this approach for dietary control. Most studies did not implement strategies to ensure compliance to dietary interventions and/or control energy intake during dietary interventions. The literature that has contributed to the current guidelines for daily CHO intake is lacking in research that is specific to, or adequately addresses, the female athlete. Redressing this imbalance is of high priority to ensure that the female athlete receives evidence-based recommendations that consider her specific needs.
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Background Dietary patterns which exclude whole food groups, such as vegetarian, vegan and low carbohydrate high fat diet (LCHF), are increasingly popular in general public. When carefully planned, all these diets have some known benefits for health, but concerns are also raised in particular for LCHF. The quality of LCHF diet which individuals follow in real life without supervision is not known. Methods One hundred thirty healthy individuals with stable body mass following LCHF, vegan, vegetarian and omnivorous diet for at least six months, were compared in a cross-sectional study. Diet was analyzed through 3-day food records and FFQ, anthropometric measurements were performed and serum metabolic biomarkers determined from fasting blood. Results Participants on LCHF diet had the intakes of micronutrients comparable to other groups, while the intakes of macronutrients differed in line with the definition of each diet. The intakes of saturated fats, cholesterol and animal proteins were significantly higher and the intakes of sugars and dietary fibers were lower compared to other groups. Healthy eating index 2015 in this group was the lowest. There were no differences in the levels of glucose, triacylglycerols and CRP among groups. Total and LDL cholesterol levels were significantly higher in LCHF group, in particular in participants with higher ketogenic ratio. Fatty acids intakes and intakes of cholesterol, dietary fibers and animal proteins explained 40% of variance in total cholesterol level, with saturated fatty acids being the strongest positive predictor and monounsaturated fatty acids a negative predictor. Conclusion None of the self-advised diets provided all the necessary nutrients in optimal levels. Due to the detected increased levels of serum cholesterols, selection of healthy fat sources, higher intake of dietary fibers and partial replacing of animal sources with plant sources of foods should be recommended to the individuals selecting LCFH dietary pattern. Clinical Trial Registration: ClinicalTrials.gov, identifier NCT04347213.
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Purpose: We investigated short-term (9 d) exposure to low energy availability (LEA) in elite endurance athletes during a block of intensified training on self-reported well-being, body composition and performance. Methods: Twenty-three highly trained race walkers undertook a ~ 3 w research-embedded training camp during which they undertook baseline testing and 6 d of high energy/carbohydrate (CHO) availability (40 kcal·kg FFM-1·d-1) before being allocated to 9 d continuation of this diet (HCHO: n = 10 M, 2F) or a significant decrease in energy availability to 15 kcal·kg FFM-1·d-1 (LEA: n = 10 M, 1F). A real-world 10,000 m race walking event was undertaken before (Baseline) and after (Adaptation) these phases, with races being preceded by standardized CHO fueling (8 g·kg BM-1 for 24 h and 2 g·kg BM-1 pre-race meal). Results: DXA-assessed body composition showed BM loss (2.0 kg; p < 0.001), primarily due to a 1.6 kg fat mass reduction (p < 0.001) in LEA, with smaller losses (BM: 0.9 kg; p = 0.008; fat mass: 0.9 kg; p < 0.001) in HCHO. The Recovery-Stress Questionnaire for Athletes (RESTQ-76), undertaken at the end of each dietary phase showed significant Diet*Trial effects for Overall Stress (p = 0.021), Overall Recovery (p = 0.024), Sport-Specific Stress (p = 0.003) and Sport-Specific Recovery (p = 0.012). However, improvements in race performance were similar: 4.5 ± 4.1% and 3.5 ± 1.8% for HCHO and LEA, respectively (p < 0.001). The relationship between changes in performance and pre-race BM was not significant (r = -0.08 [-0.49, 0.35]; p = 0.717). Conclusions: A series of strategically timed but brief phases of substantially restricted energy availability might achieve ideal race weight as part of a long-term periodization of physique by high performance athletes, but the relationship between BM, training quality and performance in weight-dependent endurance sports is complicated.
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Human skeletal muscle demonstrates remarkable plasticity, adapting to numerous external stimuli including the habitual level of contractile loading. Accordingly, muscle function and exercise capacity encompass a broad spectrum, from inactive individuals with low levels of endurance and strength, to elite athletes who produce prodigious performances underpinned by pleiotropic training-induced muscular adaptations. Our current understanding of the signal integration, interpretation and output coordination of the cellular and molecular mechanisms that govern muscle plasticity across this continuum is incomplete. As such, training methods and their application to elite athletes largely rely on a "trial and error" approach with the experience and practices of successful coaches and athletes often providing the bases for "post hoc" scientific enquiry and research. This review provides a synopsis of the morphological and functional changes along with the molecular mechanisms underlying exercise adaptation to endurance- and resistance-based training. These traits are placed in the context of innate genetic and inter-individual differences in exercise capacity and performance, with special considerations given to the ageing athletes. Collectively, we provide a comprehensive overview of skeletal muscle plasticity in response to different modes of exercise, and how such adaptations translate from "molecules to medals".
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Introduction: Body composition is a fundamental indicator to define the nutritional status of the runner. Objective: The study aimed to evaluate the effects of the nutritional periodization intervention on the body composition of elite junior Djiboutian runners in middle distance. Materials and methods: The sample consisted of 22 male runners, aged between 16 and 18 years. For the assessment, an experiment consisting of 11 subjects in the control group and 11 in the experimental roup was designed. As anthropometric measurements, weight, height and six adipose tissue were taken to evaluate the percentage of fat, adiposity index, body mass index and active body substance index, since, in order to monitor the proposed intervention, an interview of reminder 24 hours seven days. Results: A periodized diet was designed, with the manipulation of carbohydrates. Nutritional periodization with high and low carbohydrate intake for 12 weeks significantly (p<0.05) decreased percentage fat without altering body weight or active body substance index in juvenile middle-distance Djiboutian runners from the experimental group. Conclusions: The exposed results contribute to improve the biomedical control of training in elite junior middle-distance runners in Djibouti, since there were data limitations on their body composition and the effect that periodized nutrition could have on these indicators.
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ABSTRACT Dietary manipulation with high-protein or high-carbohydrate content are frequently employed during elite athletic training, aiming to enhance athletic performance. Such interventions are likely to impact upon gut microbial content. This study explored the impact of acute high-protein or high-carbohydrate diets on measured endurance performance and associated gut microbial community changes. In a cohort of well-matched, highly trained endurance runners, we measured performance outcomes, as well as gut bacterial, viral (FVP), and bacteriophage (IV) communities in a double-blind, repeated-measures design randomized control trial (RCT) to explore the impact of dietary intervention with either high-protein or high-carbohydrate content. High-dietary carbohydrate improved time-trial performance by +6.5% (P
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Background: Skeletal muscle glycogen is an important energy source for muscle contraction and a key regulator of metabolic responses to exercise. Manipulation of muscle glycogen is therefore a strategy to improve performance in competitions and potentially adaptation to training. However, assessing muscle glycogen in the field is impractical, and there are no normative values for glycogen concentration at rest and during exercise. Objective: The objective of this study was to meta-analyse the effects of fitness, acute dietary carbohydrate (CHO) availability and other factors on muscle glycogen concentration at rest and during exercise of different durations and intensities. Data source and study selection: PubMed was used to search for original articles in English published up until February 2018. Search terms included muscle glycogen and exercise, filtered for humans. The analysis incorporated 181 studies of continuous or intermittent cycling and running by healthy participants, with muscle glycogen at rest and during exercise determined by biochemical analysis of biopsies. Data analysis: Resting muscle glycogen was determined with a meta-regression mixed model that included fixed effects for fitness status [linear, as maximal oxygen uptake ([Formula: see text]O2max) in mL·kg-1·min-1] and CHO availability (three levels: high, ≥ 6 g·kg-1 of CHO per day for ≥ 3 days or ≥ 7 g·kg-1 CHO per day for ≥ 2 days; low, glycogen depletion and low-CHO diet; and normal, neither high nor low, or not specified in study). Muscle glycogen during exercise was determined with a meta-regression mixed model that included fixed effects for fitness status, resting glycogen [linear, in mmol·kg-1 of dry mass (DM)], exercise duration (five levels, with means of 5, 23, 53 and 116 min, and time to fatigue), and exercise intensity (linear, as percentage of [Formula: see text]O2max); intensity, fitness and resting glycogen were interacted with duration, and there were also fixed effects for exercise modes, CHO ingestion, sex and muscle type. Random effects in both models accounted for between-study variance and within-study repeated measurement. Inferences about differences and changes in glycogen were based on acceptable uncertainty in standardised magnitudes, with thresholds for small, moderate, large and very large of 25, 75, 150 and 250 mmol·kg-1 of DM, respectively. Results: The resting glycogen concentration in the vastus lateralis of males with normal CHO availability and [Formula: see text]O2max (mean ± standard deviation, 53 ± 8 mL·kg-1·min-1) was 462 ± 132 mmol·kg-1. High CHO availability was associated with a moderate increase in resting glycogen (102, ± 47 mmol·kg-1; mean ± 90% confidence limits), whereas low availability was associated with a very large decrease (- 253, ± 30 mmol·kg-1). An increase in [Formula: see text]O2max of 10 mL·kg-1·min-1 had small effects with low and normal CHO availability (29, ± 44 and 67, ± 15 mmol·kg-1, respectively) and a moderate effect with high CHO availability (80, ± 40 mmol·kg-1). There were small clear increases in females and the gastrocnemius muscle. Clear modifying effects on glycogen utilisation during exercise were as follows: a 30% [Formula: see text]O2max increase in intensity, small (41, ± 20 mmol·kg-1) at 5 min and moderate (87-134 mmol·kg-1) at all other timepoints; an increase in baseline glycogen of 200 mmol·kg-1, small at 5-23 min (28-59 mmol·kg-1), moderate at 116 min (104, ± 15 mmol·kg-1) and moderate at fatigue (143, ± 33 mmol·kg-1); an increase in [Formula: see text]O2max of 10 mL·kg-1·min-1, mainly clear trivial effects; exercise mode (intermittent vs. continuous) and CHO ingestion, clear trivial effects. Small decreases in utilisation were observed in females (vs. males: - 30, ± 29 mmol·kg-1), gastrocnemius muscle (vs. vastus lateralis: - 31, ± 46 mmol·kg-1) and running (vs. cycling: - 70, ± 32 mmol·kg-1). Conclusion: Dietary CHO availability and fitness are important factors for resting muscle glycogen. Exercise intensity and baseline muscle glycogen are important factors determining glycogen use during exercise, especially with longer exercise duration. The meta-analysed effects may be useful normative values for prescription of endurance exercise.
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Since the introduction of the muscle biopsy technique in the late 1960s, our understanding of the regulation of muscle glycogen storage and metabolism has advanced considerably. Muscle glycogenolysis and rates of carbohydrate (CHO) oxidation are affected by factors such as exercise intensity, duration, training status and substrate availability. Such changes to the global exercise stimulus exert regulatory effects on key enzymes and transport proteins via both hormonal control and local allosteric regulation. Given the well-documented effects of high CHO availability on promoting exercise performance, elite endurance athletes are typically advised to ensure high CHO availability before, during and after high-intensity training sessions or competition. Nonetheless, in recognition that the glycogen granule is more than a simple fuel store, it is now also accepted that glycogen is a potent regulator of the molecular cell signaling pathways that regulate the oxidative phenotype. Accordingly, the concept of deliberately training with low CHO availability has now gained increased popularity amongst athletic circles. In this review, we present an overview of the regulatory control of CHO metabolism during exercise (with a specific emphasis on muscle glycogen utilization) in order to discuss the effects of both high and low CHO availability on modulating exercise performance and training adaptations, respectively.
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Deliberately training with reduced carbohydrate (CHO) availability to enhance endurance-training-induced metabolic adaptations of skeletal muscle (i.e. the ‘train low, compete high’ paradigm) is a hot topic within sport nutrition. Train-low studies involve periodically training (e.g., 30–50% of training sessions) with reduced CHO availability, where train-low models include twice per day training, fasted training, post-exercise CHO restriction and ‘sleep low, train low’. When compared with high CHO availability, data suggest that augmented cell signalling (73% of 11 studies), gene expression (75% of 12 studies) and training-induced increases in oxidative enzyme activity/protein content (78% of 9 studies) associated with ‘train low’ are especially apparent when training sessions are commenced within a specific range of muscle glycogen concentrations. Nonetheless, such muscle adaptations do not always translate to improved exercise performance (e.g. 37 and 63% of 11 studies show improvements or no change, respectively). Herein, we present our rationale for the glycogen threshold hypothesis, a window of muscle glycogen concentrations that simultaneously permits completion of required training workloads and activation of the molecular machinery regulating training adaptations. We also present the ‘fuel for the work required’ paradigm (representative of an amalgamation of train-low models) whereby CHO availability is adjusted in accordance with the demands of the upcoming training session(s). In order to strategically implement train-low sessions, our challenge now is to quantify the glycogen cost of habitual training sessions (so as to inform the attainment of any potential threshold) and ensure absolute training intensity is not compromised, while also creating a metabolic milieu conducive to facilitating the endurance phenotype.
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This case study documents the performance of an elite-level, exceptionally well fat-adapted endurance athlete, as he reintroduced carbohydrate ingestion during high-intensity training. He had followed a strict low-carbohydrate high-fat (LCHF) diet for 2 years during which he ate approximately 80 g of carbohydrate per day and trained and raced while ingesting only water. While following this diet, he earned numerous podium finishes in triathlons of various distances. However, he approached us to test whether carbohydrate supplementation during exercise would further increase his high-intensity performance without affecting his fat-adaptation. This 7-week n=1 investigation included a 4-week habitual LCHF diet phase (LCHF) during which he drank only water during training and performance trials, and a 3-week habitual diet plus carbohydrate ingestion phase (LCHF+CHO), during which he followed his usual LCHF diet but ingested 60 g/h carbohydrate during 8 high-intensity training sessions and performance trials. After each phase, rates of fat oxidation and 30 s sprint, 4 min sprint, 20 km time trial (TT), and 100 km TT performances were measured. Compared to LCHF, 20 km TT time improved by 2.8 % after LCHF+CHO, which would be a large difference in competition. There was no change in 30 s sprint power; a small improvement in 4 min sprint power (1.6 %); and a small reduction in 100 km TT time (1.1%). We conclude that carbohydrate ingestion during exercise was likely beneficial for this fat-adapted athlete during high-intensity endurance-type exercise (4-30 min) but likely did not benefit his short sprint or prolonged endurance performance.
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Purpose: The present study investigated the effects of periodic CHO restriction on endurance performance and metabolic markers in elite endurance athletes. Methods: Twenty-six male elite endurance athletes (VO2max: 65.0 ml O2[BULLET OPERATOR]kg[BULLET OPERATOR]min) completed 4 weeks of regular endurance training, while matched and randomized into two groups training with (Low) or without (High) carbohydrate (CHO) manipulation three days a week. The CHO manipulation days consisted of a 1-hr high intensity bike session in the morning, recovery for 7 hrs while consuming isocaloric diets containing either high CHO (414±2.4 g) or low CHO (79.5±1.0 g), and a 2-hr moderate bike session in the afternoon with or without CHO. VO2max, maximal fat oxidation and power output during a 30-min time trial (TT) were determined before and after the training period. The TT was undertaken after 90 mins of intermittent exercise with CHO provision before the training period and both CHO and placebo after the training period. Muscle biopsies were analyzed for glycogen, citrate synthase (CS) and β-hydroxyacyl-coenzyme A dehydrogenase (HAD) activity, carnitine palmitoyltransferase (CPT1b) and phosphorylated acetyl-CoA carboxylase (pACC). Results: The training effects were similar in both groups for all parameters. On average, VO2max and power output during the 30-min TT increased by 5 ± 1% (P<0.05) and TT performance was similar after CHO and placebo during the preload phase. Training promoted overall increases in glycogen content (18 ± 5%), CS activity (11 ± 5%) and pACC (38 ± 19%) (P<0.05) with no differences between groups. HAD activity and CPT1b protein content remained unchanged. Conclusion: Superimposing periodic CHO restriction to 4 weeks of regular endurance training had no superior effects on performance and muscle adaptations in elite endurance athletes.
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Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown. Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL). Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C2C12 cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells. Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.
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It is becoming increasingly clear that adaptations, initiated by exercise, can be amplified or reduced by nutrition. Various methods have been discussed to optimize training adaptations and some of these methods have been subject to extensive study. To date, most methods have focused on skeletal muscle, but it is important to note that training effects also include adaptations in other tissues (e.g., brain, vasculature), improvements in the absorptive capacity of the intestine, increases in tolerance to dehydration, and other effects that have received less attention in the literature. The purpose of this review is to define the concept of periodized nutrition (also referred to as nutritional training) and summarize the wide variety of methods available to athletes. The reader is referred to several other recent review articles that have discussed aspects of periodized nutrition in much more detail with primarily a focus on adaptations in the muscle. The purpose of this review is not to discuss the literature in great detail but to clearly define the concept and to give a complete overview of the methods available, with an emphasis on adaptations that are not in the muscle. Whilst there is good evidence for some methods, other proposed methods are mere theories that remain to be tested. ‘Periodized nutrition’ refers to the strategic combined use of exercise training and nutrition, or nutrition only, with the overall aim to obtain adaptations that support exercise performance. The term nutritional training is sometimes used to describe the same methods and these terms can be used interchangeably. In this review, an overview is given of some of the most common methods of periodized nutrition including ‘training low’ and ‘training high’, and training with low- and high-carbohydrate availability, respectively. ‘Training low’ in particular has received considerable attention and several variations of ‘train low’ have been proposed. ‘Training-low’ studies have generally shown beneficial effects in terms of signaling and transcription, but to date, few studies have been able to show any effects on performance. In addition to ‘train low’ and ‘train high’, methods have been developed to ‘train the gut’, train hypohydrated (to reduce the negative effects of dehydration), and train with various supplements that may increase the training adaptations longer term. Which of these methods should be used depends on the specific goals of the individual and there is no method (or diet) that will address all needs of an individual in all situations. Therefore, appropriate practical application lies in the optimal combination of different nutritional training methods. Some of these methods have already found their way into training practices of athletes, even though evidence for their efficacy is sometimes scarce at best. Many pragmatic questions remain unanswered and another goal of this review is to identify some of the remaining questions that may have great practical relevance and should be the focus of future research.
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The gastrointestinal (GI) tract plays a critical role in delivering carbohydrate and fluid during prolonged exercise and can therefore be a major determinant of performance. The incidence of GI problems in athletes participating in endurance events is high, indicating that GI function is not always optimal in those conditions. A substantial body of evidence suggests that the GI system is highly adaptable. Gastric emptying as well as stomach comfort can be “trained” and perceptions of fullness decreased; some studies have suggested that nutrient-specific increases in gastric emptying may occur. Evidence also shows that diet has an impact on the capacity of the intestine to absorb nutrients. Again, the adaptations that occur appear to be nutrient specific. For example, a high-carbohydrate diet will increase the density of sodium-dependent glucose-1 (SGLT1) transporters in the intestine as well as the activity of the transporter, allowing greater carbohydrate absorption and oxidation during exercise. It is also likely that, when such adaptations occur, the chances of developing GI distress are smaller. Future studies should include more human studies and focus on a number of areas, including the most effective methods to induce gut adaptations and the timeline of adaptations. To develop effective strategies, a better understanding of the exact mechanisms underlying these adaptations is important. It is clear that “nutritional training” can improve gastric emptying and absorption and likely reduce the chances and/or severity of GI problems, thereby improving endurance performance as well as providing a better experience for the athlete. The gut is an important organ for endurance athletes and should be trained for the conditions in which it will be required to function.
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Due to gastrointestinal tract adaptability, the study aimed to determine the impact of gut-training protocol over 2 weeks on gastrointestinal status, blood glucose availability, fuel kinetics, and running performance. Endurance runners (n = 25) performed a gut-challenge trial (GC1), consisting of 2 h running exercise at 60% V̇O2max whilst consuming gel-discs containing 30 g carbohydrates (2:1 glucose/fructose, 10% w/v) every 20 min and a 1 h distance test. Participants were then randomly assigned to a carbohydrate gel-disc (CHO-S), carbohydrate food (CHO-F), or placebo (PLA) gut-training group for 2 weeks of repetitive gut-challenge intervention. Participants then repeated a second gut-challenge trial (GC2). Gastrointestinal symptoms reduced in GC2 on CHO-S (60%; p = 0.008) and CHO-F (63%; p = 0.046); reductions were greater than PLA (p < 0.05). H2 peak was lower in GC2 on CHO-S (mean (CI): 6 (4–8) ppm) compared with CHO-F (9 (6–12) ppm) and PLA (12 (2–21) ppm) (trial × time: p < 0.001). Blood glucose concentration was higher in GC2 on CHO-S (7.2 (6.3–8.1) mmol·L⁻¹) compared with CHO-F (6.1 (5.7–6.5) mmol·L⁻¹) and PLA (6.2 (4.9–7.5) mmol·L⁻¹) (trial × time: p = 0.015). No difference in oxidation rates, plasma I-FABP, and cortisol concentrations were observed between groups and trials. Distance test improved on CHO-S (5.2%) and CHO-F (4.3%) in GC2, but not on PLA (–2.1%) (trial × time: p = 0.009). Two weeks of gut-training with CHO-S and CHO-F improved gastrointestinal symptoms and running performance compared with PLA. CHO-S also reduced malabsorption and increased blood glucose availability during endurance running compared with PLA.
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Background: "Sleep-low" consists of a sequential periodization of carbohydrate (CHO) availability-low glycogen recovery after "train high" glycogen-depleting interval training, followed by an overnight-fast and light intensity training ("train low") the following day. This strategy leads to an upregulation of several exercise-responsive signaling proteins, but the chronic effect on performance has received less attention. We investigated the effects of short-term exposure to this strategy on endurance performance. Methods: Following training familiarization, 11 trained cyclists were divided into two groups for a one-week intervention-one group implemented three cycles of periodized CHO intake to achieve the sleep-low strategy over six training sessions (SL, CHO intake: 6 g·kg(-1)·day(-1)), whereas the control group consumed an even distribution of CHO over the day (CON). Tests were a 2 h submaximal ride and a 20 km time trial. Results: SL improved their performance (mean: +3.2%; p < 0.05) compared to CON. The improvement was associated with a change in pacing strategy with higher power output during the second part of the test. No change in substrate utilization was observed after the training period for either group. Conclusion: Implementing the "sleep-low" strategy for one week improved performance by the same magnitude previously seen in a three-week intervention, without any significant changes in selected markers of metabolism.
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Optimising training and performance through nutrition strategies is central to supporting elite sportspeople, much of which has focussed on manipulating the relative intake of carbohydrate and fat and their contributions as fuels for energy provision. The ketone bodies, namely acetoacetate, acetone, and β-hydroxybutyrate (βHB), are produced in the liver during conditions of reduced carbohydrate availability and serve as an alternative fuel source for peripheral tissues including brain, heart and skeletal muscle. Ketone bodies are oxidised as a fuel source during exercise, are markedly elevated during the post-exercise recovery period, and the ability to utilise ketone bodies is higher in exercise-trained skeletal muscle. The metabolic actions of ketone bodies can alter fuel selection through attenuating glucose utilisation in peripheral tissues, anti-lipolytic effects on adipose tissue, and attenuation of proteolysis in skeletal muscle. Moreover, ketone bodies can act as signalling metabolites with βHB acting as an inhibitor of histone deacetylases, an important regulator of the adaptive response to exercise in skeletal muscle. Recent development of ketone esters facilitates acute ingestion of βHB that results in nutritional ketosis without necessitating restrictive dietary practices. Initial reports suggest this strategy alters the metabolic response to exercise and improves exercise performance, while other lines of evidence suggest roles in recovery from exercise. The present review focuses on the physiology of ketone bodies during and after exercise and in response to training, with specific interest in exploring the physiological basis for exogenous ketone supplementation and potential benefits for performance and recovery in athletes.
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Since the pioneering studies conducted in the 1960s in which glycogen status was investigated utilizing the muscle biopsy technique, sports scientists have developed a sophisticated appreciation of the role of glycogen in cellular adaptation and exercise performance, as well as sites of storage of this important metabolic fuel. While sports nutrition guidelines have evolved during the past decade to incorporate sport-specific and periodized manipulation of carbohydrate (CHO) availability, athletes attempt to maximise muscle glycogen synthesis between important workouts or competitive events so that fuel stores closely match to the demands of the prescribed exercise. Therefore, it is important to understand the factors that enhance or impair this biphasic process. In the early post-exercise period (0-4 h), glycogen depletion provides a strong drive for its own resynthesis, with the provision of carbohydrate (CHO; ~ 1 g/kg body mass [BM]) optimizing this process. During the later phase of recovery (4-24 h), CHO intake should meet the anticipated fuel needs of the training/competition, with the type, form and pattern of intake being less important than total intake. Dietary strategies that can enhance glycogen synthesis from sub-optimal amounts of CHO or energy intake are of practical interest to many athletes; in this scenario, the co-ingestion of protein with CHO can assist glycogen storage. Future research should identify other factors that enhance the rate of synthesis of glycogen storage in a limited time-frame, improve glycogen storage from a limited CHO intake or increase muscle glycogen supercompensation.
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Elite athletes and coaches are in a constant search for training methods and nutritional strategies to support training and recovery efforts that may ultimately maximize athletes' performance. Recently, there has been a re-emerging interest in the role of ketone bodies in exercise metabolism, with considerable media speculation about ketone body supplements being routinely used by professional cyclists. Ketone bodies can serve as an important energy substrate under certain conditions, such as starvation, and can modulate carbohydrate and lipid metabolism. Dietary strategies to increase endogenous ketone body availability (i.e., a ketogenic diet) require a diet high in lipids and low in carbohydrates for ~4 days to induce nutritional ketosis. However, a high fat, low carbohydrate ketogenic diet may impair exercise performance via reducing the capacity to utilize carbohydrate, which forms a key fuel source for skeletal muscle during intense endurance-type exercise. Recently, ketone body supplements (ketone salts and esters) have emerged and may be used to rapidly increase ketone body availability, without the need to first adapt to a ketogenic diet. However, the extent to which ketone bodies regulate skeletal muscle bioenergetics and substrate metabolism during prolonged endurance-type exercise of varying intensity and duration remains unknown. Therefore, at present there are no data available to suggest that ingestion of ketone bodies during exercise improves athletes' performance under conditions where evidence-based nutritional strategies are applied appropriately.
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Using an amalgamation of previously studied "train-low" paradigms, we tested the effects of reduced carbohydrate (CHO) but high leucine availability on cell-signaling responses associated with exercise-induced regulation of mitochondrial biogenesis and muscle protein synthesis (MPS). In a repeated-measures crossover design, 11 males completed an exhaustive cycling protocol with high CHO availability before, during, and after exercise (HIGH) or alternatively, low CHO but high protein (leucine enriched) availability (LOW + LEU). Muscle glycogen was different (P < 0.05) pre-exercise (HIGH: 583 ± 158, LOW + LEU: 271 ± 85 mmol kg(-1) dw) but decreased (P < 0.05) to comparable levels at exhaustion (≈100 mmol kg(-1) dw). Despite differences (P < 0.05) in exercise capacity (HIGH: 158 ± 29, LOW + LEU: 100 ± 17 min), exercise induced (P < 0.05) comparable AMPKα2 (3-4-fold) activity, PGC-1α (13-fold), p53 (2-fold), Tfam (1.5-fold), SIRT1 (1.5-fold), Atrogin 1 (2-fold), and MuRF1 (5-fold) gene expression at 3 h post-exercise. Exhaustive exercise suppressed p70S6K activity to comparable levels immediately post-exercise (≈20 fmol min(-1) mg(-1)). Despite elevated leucine availability post-exercise, p70S6K activity remained suppressed (P < 0.05) 3 h post-exercise in LOW + LEU (28 ± 14 fmol min(-1) mg(-1)), whereas muscle glycogen resynthesis (40 mmol kg(-1) dw h(-1)) was associated with elevated (P < 0.05) p70S6K activity in HIGH (53 ± 30 fmol min(-1) mg(-1)). We conclude: (1) CHO restriction before and during exercise induces "work-efficient" mitochondrial-related cell signaling but; (2) post-exercise CHO and energy restriction maintains p70S6K activity at basal levels despite feeding leucine-enriched protein. Our data support the practical concept of "fuelling for the work required" as a potential strategy for which to amalgamate train-low paradigms into periodized training programs.
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It is the position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine that the performance of, and recovery from, sporting activities are enhanced by well-chosen nutrition strategies. These organizations provide guidelines for the appropriate type, amount, and timing of intake of food, fluids, and supplements to promote optimal health and performance across different scenarios of training and competitive sport. This position paper was prepared for members of the Academy of Nutrition and Dietetics, Dietitians of Canada (DC), and American College of Sports Medicine (ACSM), other professional associations, government agencies, industry, and the public. It outlines the Academy’s, DC’s and ACSM’s stance on nutrition factors that have been determined to influence athletic performance and emerging trends in the field of sports nutrition. Athletes should be referred to a registered dietitian/nutritionist for a personalized nutrition plan. In the United States and in Canada, the Certified Specialist in Sports Dietetics (CSSD) is a registered dietitian/nutritionist and a credentialed sports nutrition expert.
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Key points: Blood glucose is an important fuel for endurance exercise. It can be derived from ingested carbohydrate, stored liver glycogen and newly synthesized glucose (gluconeogenesis). We hypothesized that athletes habitually following a low carbohydrate high fat (LCHF) diet would have higher rates of gluconeogenesis during exercise compared to those who follow a mixed macronutrient diet. We used stable isotope tracers to study glucose production kinetics during a 2 h ride in cyclists habituated to either a LCHF or mixed macronutrient diet. The LCHF cyclists had lower rates of total glucose production and hepatic glycogenolysis but similar rates of gluconeogenesis compared to those on the mixed diet. The LCHF cyclists did not compensate for reduced dietary carbohydrate availability by increasing glucose synthesis during exercise but rather adapted by altering whole body substrate utilization. Abstract: Endogenous glucose production (EGP) occurs via hepatic glycogenolysis (GLY) and gluconeogenesis (GNG) and plays an important role in maintaining euglycaemia. Rates of GLY and GNG increase during exercise in athletes following a mixed macronutrient diet; however, these processes have not been investigated in athletes following a low carbohydrate high fat (LCHF) diet. Therefore, we studied seven well-trained male cyclists that were habituated to either a LCHF (7% carbohydrate, 72% fat, 21% protein) or a mixed diet (51% carbohydrate, 33% fat, 16% protein) for longer than 8 months. After an overnight fast, participants performed a 2 h laboratory ride at 72% of maximal oxygen consumption. Glucose kinetics were measured at rest and during the final 30 min of exercise by infusion of [6,6-(2) H2 ]-glucose and the ingestion of (2) H2 O tracers. Rates of EGP and GLY both at rest and during exercise were significantly lower in the LCHF group than the mixed diet group (Exercise EGP: LCHF, 6.0 ± 0.9 mg kg(-1) min(-1) , Mixed, 7.8 ± 1.1 mg kg(-1) min(-1) , P < 0.01; Exercise GLY: LCHF, 3.2 ± 0.7 mg kg(-1) min(-1) , Mixed, 5.3 ± 0.9 mg kg(-1) min(-1) , P < 0.01). Conversely, no difference was detected in rates of GNG between groups at rest or during exercise (Exercise: LCHF, 2.8 ± 0.4 mg kg(-1) min(-1) , Mixed, 2.5 ± 0.3 mg kg(-1) min(-1) , P = 0.15). We conclude that athletes on a LCHF diet do not compensate for reduced glucose availability via higher rates of glucose synthesis compared to athletes on a mixed diet. Instead, GNG remains relatively stable, whereas glucose oxidation and GLY are influenced by dietary factors.
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Purpose: We investigated the effect of a chronic dietary periodization strategy on endurance performance in trained athletes. Methods: 21 triathletes (V[Combining Dot Above]O2max: 58.7 ± 5.7 mL·min·kg) were divided into 2 groups: a "sleep-low" (SL, n = 11) and a control group (CON, n = 10) consumed the same daily carbohydrate (CHO) intake (6 g·kg·d) but with different timing over the day to manipulate CHO availability before and after training sessions. The "sleep low" strategy consisted of a 3-week training/diet intervention comprising three blocks of diet/exercise manipulations: 1) "train-high" interval training sessions (HIT) in the evening with high-CHO availability; 2) overnight CHO restriction ("sleeping-low"), and 3) "train-low" sessions with low endogenous and exogenous CHO availability. The CON group followed the same training program but with high CHO availability throughout training sessions (no CHO restriction overnight, training sessions with exogenous CHO provision). Results: There was a significant improvement in delta efficiency during submaximal cycling for SL versus CON (CON: +1.4 ± 9.3 %, SL: +11 ± 15 %, P<0.05). SL also improved supra-maximal cycling to exhaustion at 150% of peak aerobic power (CON: +1.63 ± 12.4 %, SL: +12.5 ± 19.0 %; P = 0.06) and 10 km running performance (CON: -0.10 ± 2.03 %, SL: -2.9 ± 2.15 %; P < 0.05). Fat mass was decreased in SL (CON: -2.6 ± 7.4; SL: -8.5 ± 7.4 %PRE, P < 0.01), but not lean mass (CON: -0.22 ± 1.0; SL: -0.16 ± 1.7 %PRE). Conclusion: Short-term periodization of dietary CHO availability around selected training sessions promoted significant improvements in submaximal cycling economy, as well as supra-maximal cycling capacity and 10 km running time in trained endurance athletes.
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Background: Many successful ultra-endurance athletes have switched from a high-carbohydrate to a low-carbohydrate diet, but they have not previously been studied to determine the extent of metabolic adaptations. Methods: Twenty elite ultra-marathoners and ironman distance triathletes performed a maximal graded exercise test and a 180 min submaximal run at 64% VO2max on a treadmill to determine metabolic responses. One group habitually consumed a traditional high-carbohydrate (HC: n=10, %carbohydrate:protein:fat=59:14:25) diet, and the other a low-carbohydrate (LC; n=10, 10:19:70) diet for an average of 20 months (range 9 to 36 months). Results: Peak fat oxidation was 2.3-fold higher in the LC group (1.54±0.18 vs 0.67±0.14 g/min; P=0.000) and it occurred at a higher percentage of VO2max (70.3±6.3 vs 54.9±7.8%; P=0.000). Mean fat oxidation during submaximal exercise was 59% higher in the LC group (1.21±0.02 vs 0.76±0.11 g/min; P=0.000) corresponding to a greater relative contribution of fat (88±2 vs 56±8%; P=0.000). Despite these marked differences in fuel use between LC and HC athletes, there were no significant differences in resting muscle glycogen and the level of depletion after 180 min of running (-64% from pre-exercise) and 120 min of recovery (-36% from pre-exercise). Conclusion: Compared to highly trained ultra-endurance athletes consuming an HC diet, long-term keto-adaptation results in extraordinarily high rates of fat oxidation, whereas muscle glycogen utilization and repletion patterns during and after a 3 hour run are similar.
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During the period 1985-2005, studies examined the proposal that adaptation to a low-carbohydrate (<25 % energy), high-fat (>60 % energy) diet (LCHF) to increase muscle fat utilization during exercise could enhance performance in trained individuals by reducing reliance on muscle glycogen. As little as 5 days of training with LCHF retools the muscle to enhance fat-burning capacity with robust changes that persist despite acute strategies to restore carbohydrate availability (e.g., glycogen supercompensation, carbohydrate intake during exercise). Furthermore, a 2- to 3-week exposure to minimal carbohydrate (<20 g/day) intake achieves adaptation to high blood ketone concentrations. However, the failure to detect clear performance benefits during endurance/ultra-endurance protocols, combined with evidence of impaired performance of high-intensity exercise via a down-regulation of carbohydrate metabolism led this author to dismiss the use of such fat-adaptation strategies by competitive athletes in conventional sports. Recent re-emergence of interest in LCHF diets, coupled with anecdotes of improved performance by sportspeople who follow them, has created a need to re-examine the potential benefits of this eating style. Unfortunately, the absence of new data prevents a different conclusion from being made. Notwithstanding the outcomes of future research, there is a need for better recognition of current sports nutrition guidelines that promote an individualized and periodized approach to fuel availability during training, allowing the athlete to prepare for competition performance with metabolic flexibility and optimal utilization of all muscle substrates. Nevertheless, there may be a few scenarios where LCHF diets are of benefit, or at least are not detrimental, for sports performance.
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Bone resorption is increased following running, with no change in bone formation. Feeding during exercise might attenuate this increase, preventing associated problems for bone. To investigate the immediate and short-term bone metabolic responses to carbohydrate (CHO) feeding during treadmill running. Ten men completed two 7 d trials, once being fed CHO (8% glucose immediately before, every 20 min during and immediately after exercise at a rate of 0.7 gCHO·kg(-1)BM·h(-1)) and once placebo (PBO). On day 4 of each trial, participants completed a 120 min treadmill run at 70% VO2max. Blood was taken at baseline (BASE) immediately after exercise (EE), after 60 (R1) and 120 (R2) min of recovery and on 3 follow-up days (FU1-FU3). Markers of bone resorption (β-CTX) and formation (P1NP) were measured, along with OC, PTH, ACa, PO4, GLP-2, IL-6, insulin, cortisol, leptin and OPG. Area under the curve was calculated in terms of the immediate (BASE, EE, R1 and R2) and short-term (BASE, FU1, FU2 and FU3) responses to exercise. β-CTX, P1NP and IL-6 responses to exercise were significantly lower in the immediate post-exercise period with CHO feeding (β-CTX: P=0.028; P1NP: P=0.021; IL-6: P=0.036), although there was no difference in the short-term response (β-CTX: P=0.856; P1NP: P=0.721; IL-6: P=0.327). No other variable was significantly affected by CHO feeding during exercise. CHO feeding during exercise attenuated the β-CTX and P1NP responses in the hours but not days following exercise, indicating an acute effect of CHO feeding on bone turnover. Copyright © 2015, Journal of Applied Physiology.
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We tested the hypothesis that carbohydrate mouth rinsing, alone or in combination with caffeine, augments high-intensity interval (HIT) running capacity undertaken in a carbohydrate-restricted state. Carbohydrate restriction was achieved by performing high-intensity running to volitional exhaustion in the evening prior to the main experimental trials and further refraining from carbohydrate intake in the post-exercise and overnight period. On the subsequent morning, eight males performed 45-min steady-state (SS) exercise (65% [Formula: see text]) followed by HIT running to exhaustion (1-min at 80% [Formula: see text]interspersed with 1-min walking at 6 km/h). Subjects completed 3 trials consisting of placebo capsules (administered immediately prior to SS and immediately before HIT) and placebo mouth rinse at 4-min intervals during HIT (PLACEBO), placebo capsules but 10% carbohydrate mouth rinse (CMR) at corresponding time-points or finally, caffeine capsules (200 mg per dose) plus 10% carbohydrate mouth rinse (CAFF + CMR) at corresponding time-points. Heart rate, capillary glucose, lactate, glycerol and NEFA were not different at exhaustion during HIT (P > 0.05). However, HIT capacity was different (P < 0.05) between all pair-wise comparisons such that CAFF + CMR (65 ± 26 min) was superior to CMR (52 ± 23 min) and PLACEBO (36 ± 22 min). We conclude that carbohydrate mouth rinsing and caffeine ingestion improves exercise capacity undertaken in carbohydrate-restricted states. Such nutritional strategies may be advantageous for those athletes who deliberately incorporate elements of training in carbohydrate-restricted states (i.e. the train-low paradigm) into their overall training programme in an attempt to strategically enhance mitochondrial adaptations of skeletal muscle.
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