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Nutrition and Performance in Sport

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Christophe Hausswirth

Chapter 5. Nutrition and physical composition

Topic 2. Nutrition and control of muscle mass under situation of metabolic challenge

Xavier Bigard et Alexandra Malgoyre

Résumé

The control of muscle mass results from the balance between the levels of contractile protein synthesis and breakdown. Physical exercise and nutrition both influence muscle mass through modifications of the net balance between protein synthesis and protein degradation rates.
Several studies showed that the muscle protein acute synthesis was firstly regulated through the translation initiation of messenger RNA (mRNA) by activation of a variety of intracellular signalling proteins, especially those involved within the signalling cascade of the mammalian target of rapamycin (mTOR). In humans, the stimulation of muscle protein synthesis after a meal or physical exercise is accompanied by increased activity of the mTOR signalling pathway, after phosphorylation of 70 kDa ribosomal protein S6 kinase (p70S6K or S6K1) and its target, the S6 ribosomal protein (rpS6). There are now a lot of scientific evidences that demonstrate the major role played by the mTORC1 complex in the regulation of muscle mass in response to a large variety of stimulus, including nutrients, growth factors and insulin.
More recently, the major impact of the 5’AMP-activated protein kinase (AMPK), an intracellular energy sensor, on the control of muscle cells’size has been updated. AMPK, that plays a key role on the control of the cell energy homeostasis is activated during physical exercise in skeletal muscles. This AMPK activation is vital for restoring intracellular energy balance via inhibition of energy-consuming biosynthetic processes and concomitant activation of pathways that increase ATP production. AMPK activation reduces protein synthesis by 45% in homogenates of muscles, and decreases the activation of both mTOR and rpS6 kinases. Decreased protein synthesis as a result of mTORC1 signaling inhibition could explain a number of muscle adaptations specific to the physical training, including the fact that in general, training in endurance is not associated to increased muscle mass. Many other targets downstream from mTOR could also play a major role in skeletal muscle physiology, such as the FoxO (
Forkhead box O) family of transcription factors which stimulate muscle proteins breakdown through upregulation of atrogenes.
Prolonged, high-intensity sport events, such as ironman Triathlons, raids or ultra-endurance races, are always performed in negative energy balance. This type of metabolic stress leads to AMPK activation and makes energy intake of particular importance during the event. The role played by nutrition to prevent the effects of prolonged high-intensity exercise on negative energy balance, and then muscle atrophy, has to be considered in order to reach two main objectives. First, to prevent glycogen depletion and provide enough carbohydrate to working skeletal muscles during the race (and then minimize AMPK activation), second to favor the muscle protein status recovery early after the end of exhaustive exercise.

Texte intégral

1. Introduction

1Skeletal muscle is a highly plastic tissue that is permanently concomitantly submitted to both protein synthesis and breakdown. The fine control of the dynamic equilibrium between protein breakdown and protein synthesis explains changes in muscle mass (i.e. muscle atrophy or muscle growth). Studying the molecular events involved in the control of muscle protein synthesis contributes to significant progress in understanding muscle hypertrophy in response to strength training. It is also important to improve our knowledge about the molecular determinants of muscle atrophy, as reported in all situations of physical inactivity, deconditioning (in the case of non-communicable diseases) or ageing. Athletes involved in high-intensity exercise sessions, associated with energy stress, very often have a low muscle mass; this can be an advantage in some situations, but also sometimes be a handicap for physical performances. The impact of reduced muscle mass on health and the incidence of chronic diseases have to be examined in the future.

2The aim of this presentation is 1) to suggest a mechanistic link between the metabolic consequences of acute physical exercise and the control of muscle mass in athletes, especially for sports associated with stoichiometric energy constraints within myofibers, and, 2) to define the role played by nutrition in maintaining a muscle mass consistent with the athlete’s health. Addressing these issues leads us to a scientific domain combining nutrition, exercise physiology and cellular biology.

2. Control of muscle mass

3The early 2000s were a real turning point regarding our knowledge about the biological determinants of the cellular mechanisms that account for the adaptive responses of the contractile and metabolic muscle phenotype to physical training. It was shown that protein kinase B (Akt), a serine/threonine kinase mainly present in the muscle, played a role in the control of skeletal muscle mass (Bodine et al. 2001). As shown in figure 1, the Akt kinase is integrated into an intracellular signalling pathway that links biological and mechanical signals (including IGF-1 (insulin-like growth factor-1), insulin and integrins) to mTOR kinase (mammalian target of rapamycin) and GSK3 (glycogen synthase kinase 3). Activation of this signalling pathway contributes to increasing the amount of cellular ribosomes (through mTOR and p70S6K protein) and to initiate the translation of mRNA resulting from the expression of genes into proteins, first native, then mature and functional. This signalling pathway is thus strongly involved in the control of the rate of protein synthesis and in skeletal muscle hypertrophy, especially in response to resistance training (Léger et al. 2006).

Figure 1: Schematic representation of how Akt, mTOR, and p70S6k work together to control muscle growth. This intracellular signalling pathway controls the translation of messenger RNA (mRNA) molecules – which are transcribed genes – into functional proteins.

Figure 1: Schematic representation of how Akt, mTOR, and p70S6k work together to control muscle growth. This intracellular signalling pathway controls the translation of messenger RNA (mRNA) molecules – which are transcribed genes – into functional proteins.

4Parallel to the biological control of protein synthesis, a direct regulation of the rate of contractile and structural proteolysis through the activation of ubiquitine-proteasome pathway contributes to the control of muscle mass. The downregulation of the Akt kinase activity permits the transcription of MAFbx (atrogin-1) and MuRF1 (muscle ring finger-1), two muscle-specific E3 ubiquitin-ligases that play a role in muscle atrophy [Fig. 2]. The transcription of genes coding for these two proteins is partly under the control of the Forkhead box O1 (FoxO1) transcription factor, which contributes to the regulation of protein breakdown by the lysosome. Experimental data are not unequivocal, but it seems likely that MuRF1 and MAFbx are involved in the amyotrophy reported in a lot of situations of physical inactivity (Jones et al. 2004). At the experimental level, the regulation of MuRF1 and MAFbx was shown to depend on the type of exercise, the time of blood samples compared to the end of exercise, and of the training status of the subjects (review of Russell, 2010). However, these proteasome activator proteins and the rate of protein degradation are fairly well coregulated.

Figure 2: Relationship between the IGF-1/Akt/mTOR signalling pathway, controlling muscle protein synthesis, and the ubiquitin-proteasome pathway [atrogin-1 (MAFbx) and MuRF1], controlling muscle protein breakdown.

Figure 2: Relationship between the IGF-1/Akt/mTOR signalling pathway, controlling muscle protein synthesis, and the ubiquitin-proteasome pathway [atrogin-1 (MAFbx) and MuRF1], controlling muscle protein breakdown.

5In most situations, protein synthesis and breakdown are coherently regulated. Thus, muscle anabolism results from an increase in the rate of protein synthesis and decrease in the rate of protein degradation, and muscle catabolism results from the opposite process. This logical link between protein synthesis and proteolysis relies on several molecular mechanisms, including a link between the Akt kinase and the FoxO transcription factor that controls the transcription of MuRF1 and MAFbx genes. The Akt kinase activation by the IGF-1-dependent signalling triggers FoxO phosphorylation. Phosphorylated FoxO is thus retained in the sarcoplasm, where it cannot regulate the transcription of its target genes (Biggs et al. 1999). Therefore, in reaction to anabolic stimuli such as those generated by IGF-1, there are simultaneous and parallel activation of proteosynthesis by Akt, mTOR, GSK3 and p70S6K (Fig. 1), and an inhibition of the protein breakdown related to FoxO inactivation, and then inhibition of the ubiquitin-proteasome pathway (Fig. 2).

6We will now go on to examine some of the consequences of exercise of prolonged high-intensity exercise on muscle protein metabolism.

3. Prolonged exercise and muscle metabolism

7Resistance training is known to favour muscle anabolism, but the rate of protein synthesis can be repressed during intense muscle activity. Physical exercises of high intensity, including resistance exercises, lead to enhanced AMPK activity (AMP-activated protein Kinase) after phosphorylation of its α2 sub-unit, inhibition of the mTOR activity, and then decrease the rate of protein synthesis (Dreyer et al. 2006).

8AMPK is activated by cellular stress associated with ATP depletion, together with a concomitant rise in the AMP/ATP ratio (Hardie, 2004). This enzymatic system acts as a sensor of cellular energy by monitoring the cellular AMP/ATP ratio; it is activated in all metabolic situations of imbalance between the levels of ATP consumption and synthesis by energy pathways; high intensity physical exercises lead to physiologic stress that activates AMPK as ATP consumption increases during muscle contractions. AMPK activity in recruited skeletal muscles is directly linked to strength and muscle power (Wadley et al. 2006), as well as to training status (Richard et al. 2008).

9In situations of high energy stress, AMPK activation can affect mTOR activity through a variety of molecular mechanisms, including direct mTOR phosphorylation or inhibition of mTOR regulators (Inoki et al. 2003; Cheng et al. 2004; Hardie, 2008) [Fig. 3]. Whatever the molecular mechanisms involved, AMPK is an important negative regulator of the Akt/mTOR pathway in skeletal muscle. It has been previously shown that the pharmacological activation of AMP by AICAR (5-aminoimidazole-4-carboxamide-1-β-D-ribonucleoside) leads to mTOR inhibition and decreased the rate of protein synthesis (Williamson et al. 2006). These results reflect the biological mechanisms behind the negative influence of the cell energy status (in the skeletal muscle) on muscle anabolism.

Figure 3: Inhibitors of intracellular signalling pathways involved in muscle protein synthesis.

Figure 3: Inhibitors of intracellular signalling pathways involved in muscle protein synthesis.

10Another important mechanism negatively regulating mTOR activity has been recently highlighted. Two protein factors, called REDD1 (REgulated in Development and DNA damage responses 1) and REDD2 that are expressed during conditions of intense cellular stress (exposure to hypoxia, intoxication with alcohol, dexamethasone treatment, physical exercise, etc.) have been shown to inhibit the mTOR kinase activity and then the Akt/mTOR signalling pathway (De Young et al. 2008; Murakami et al. 2011) [Fig. 3]. The transcription level of REDD1, at least in hypoxic conditions, is under the control of the transcription factor HIF-1. REDD1 protein levels increase in skeletal muscle at the end of prolonged endurance exercise, with an expression level correlating with the exercise intensity (Murakami et al. 2011). The mechanisms controlling REDD1 expression in skeletal muscle have not been studied extensively, but they might be linked to the level of cellular hypoxia induced by repeated contractions. Therefore, this regulatory protein could also play a role in the alteration of the skeletal muscle protein anabolism during extreme exercise. Once it has been expressed, for instance in response to hypoxia, REDD1 could alter mTOR activity, leading to decreased phosphorylation of its targets P70S6K and 4E-BP1 (Sofer et al. 2005).

11All environmental situations causing major alteration of the muscle energy status are associated with activation of the cellular energy sensors AMPK or REDD1 that inhibit the rate of muscle protein synthesis, to minimize ATP consumption, and enhance the rate of protein breakdown. These molecular interactions were identified in myofibers, and demonstrate the potential negative consequences of high-intensity prolonged exercises on the maintenance of skeletal muscle mass. Endurance exercises are expected to activate negative regulators of muscle mass and inhibit muscle hypertrophy, as observed with concurrent training, combining resistance and endurance exercises.

4. Interaction between intracellular energy status and muscle build

12Since the pioneering work of Hickson (1980), a lot of studies clearly showed that simultaneously training for both strength and endurance results in compromised adaptations of muscle growth that highlight the difficulties to possess high levels of both muscle strength and power, and resistance to fatigue. Concurrent training, characterised by concomitant exercises of strength and endurance, has been shown to result in impaired muscle mass growth and strength improvements when compared to strength training alone (Hickson et al. 1980) [Fig. 4]. The type, composition and planning of concurrent training programmes impact on the expected adaptive changes on aerobic endurance and development of muscle mass. However, the impaired strength and power improvements reported in response to concurrent training can probably be explained, at least partly, by the biological consequences of the myofiber energy status (Izquierdo et al. 2005).

Figure 4: Weekly changes to strength developed in the thigh extensor muscles in response to endurance (E), resistance (S) and concurrent training (S + E) programmes. Concurrent training combines both endurance and resistance exercises. Strength performances increase more slowly, and then decrease after seven weeks of concurrent training. This contrasts with the effects observed after resistance training.

Figure 4: Weekly changes to strength developed in the thigh extensor muscles in response to endurance (E), resistance (S) and concurrent training (S + E) programmes. Concurrent training combines both endurance and resistance exercises. Strength performances increase more slowly, and then decrease after seven weeks of concurrent training. This contrasts with the effects observed after resistance training.

Adapted from Hickson et al. (1980).

13The biological mechanisms reported above contribute to explain the impaired strength gains observed over the course of a concurrent training programme, related to the cellular metabolic stress induced by endurance exercises. Prolonged high-intensity exercises (or sports events) thus have potentially negative effects on muscle mass growth, related first on exercise duration, second, on the period during which the rate of protein synthesis decreased, and third on the extension of this inhibition during the recovery phase. Many issues need to be addressed in the near future, including determining the duration of the impairment of protein synthesis during recovery from exercise, and how long it takes to recover muscle anabolism. These issues remain determinant for improving our knowledge on the biological and nutritional control of muscle mass.

14Within the context of high-intensity exercise including metabolic stress, the athlete must, with simple nutritional rules, first minimize the activation of sensor of the cellular energy status during physical exercise itself, and second ensure optimal availability of amino acids as early as possible during recovery.

5. Suitable nutritional behaviour

15The purpose of dietary recommendations is to provide the energy intake during exercise, and to ensure both energy and protein intake during the immediate post-exercise recovery. The aim of energy intake during exercise is to minimize the activation of metabolic stress captors such as AMPK and/or REDD1 protein, and the dietary recommendations during the recovery phase must ensure increased muscle protein synthesis and reduced protein breakdown, thus promoting muscle mass maintenance.

6. Energy intake during the event

16There is today a host of scientific data about nutritional intake during high-intensity prolonged exercises that require an optimal availability of energy. During events such as ultramarathons, cycling races, long-distance triathlon, or long raids with several stages, energy requirements are covered by several kinds of substrates: glucose, fatty acids, and possibly amino acids such as leucine, that can be used by oxidation. Fatty acid oxidation during exercise contributes to spare glucose stores, and the only way to favour oxidation of this substrate naturally present in great amounts in the body, is physical training. Glucose availability during high-intensity exercises being limited by the extent of glycogen stores, it is recommended to ensure regular carbohydrate intake during exercise. The best compromise between carbohydrate requirements, practical dietary concerns, water intake and digestive tolerance, consists in consuming drinks providing 80 to 100 kcal carbohydrate per hour. It is important to adapt the drink composition according to both the water and carbohydrate requirements, as determined by the climate and environmental conditions. This adaptation will favour either energy intake (drinks containing between 60 to 80 g.l−1 of carbohydrates), or water intake (diluted drinks containing between 20 and 40 g.l−1 of carbohydrates) [Bigard and Guézennec, 2007]. During long-lasting sport events that require high energy levels, athletes must complete the carbohydrate intake through drinks, by high-carbohydrate diets. The consumption of energy bars or carbohydrate-dense gels is an excellent way to ensure additional energy intake. Therefore, the oxidation of leucine during long-lasting exercise will be limited and protein breakdown as a source of energy will be reduced.

7. Nutritional intake during recovery

17As shown in a lot of studies, physical exercise affects both muscle protein degradation and synthesis. According to its intensity, duration and type, exercise is accompanied by a reduction in the rate of muscle protein synthesis, and a concomitant increase in the rate of protein breakdown; the end of exercise corresponds to a quick and intense increase in protein synthesis, while the rate of proteolysis continues to grow up to three hours after the end of exercise before returning to pre-exercise levels (Dreyer et al. 2006). During strenuous ultra-endurance exercises, including high-energy requirements, athletes must ensure an excellent availability of amino acids and energy during recovery, despite the potential inhibition of proteosynthesis after activation of the sensors of the cellular energy status.

18Amino acid availability. There has been considerable debate surrounding the ideal timing of protein ingestion to maximize post-exercise muscle protein synthesis. Recent data clearly showed that the crucial moment for the optimal availability of amino acids immediate post-exercise recovery, when the rate of muscle protein synthesis markedly increases.

19The optimal amount of proteins to provide during recovery from strenuous long-lasting exercise remains to be determined more precisely. Beyond total daily protein intake, recent studies focused on the importance of adequate quantity of protein intake immediately after exercise. It has been shown that the rate of muscle protein synthesis increased with the amount of dietary proteins during recovery, and that the estimated average requirement to maximize post-exercise muscle protein synthesis may be as high as ˜20 to 25 g for young men (Moore et al. 2009) [Fig. 5].

Figure 5: Fractional rate of protein synthesis, expressed in percentage per hour, as a function of the level of protein intake provided by food after strength exercises. Increasing dietary protein intake, up to approximately 20 g, increases the rate of protein synthesis.

Figure 5: Fractional rate of protein synthesis, expressed in percentage per hour, as a function of the level of protein intake provided by food after strength exercises. Increasing dietary protein intake, up to approximately 20 g, increases the rate of protein synthesis.

a, b, c: significant difference between groups (P<0.05). Adapted from Moore et al. (2009).

20For optimal nutritional efficiency, the nature and source of dietary proteins also needs to be determined as the nutritional efficiency of proteins depends on their biological value, but also on how fast they are digested. Food intake during recovery must provide an adequate amount of essential amino acids (isoleucine, leucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine). The quality of amino acids provided by dietary proteins is a good criterion of quality, but their postprandial bioavailability is also an essential factor for their biological efficiency. That is why the composition of dietary proteins must be corrected by their digestibility, when determining their «biological value». In general, proteins from animal origin (rich in essential amino acids and easily digestible) have a higher biological value than that of proteins of vegetable origin, even though this notion must be taken carefully. Protein intake during recovery from exercise mostly comes from industrial preparations of total proteins, protein hydrolysates or amino acid associations. The amino-acid composition of these preparations must be studied carefully: they must respect a certain balance between amino acids, considering that an insufficient amount of amino acids can be a limiting factor for protein synthesis.

21After ingestion of high-biological value proteins, the pattern of amino acid availability into the plasma depends from several factors including the food source (i.e. liquid versus solid forms of foods) (Burke et al. 2012). Another factors contribute to explain the characteristic patterns of aminoacidaemia associated with the intake of different types of dietary proteins. For instance, the two main milk protein fractions, i.e. casein and whey proteins, do not have the same digestion speed. Whey proteins remain soluble in an acid pH, are quickly released by the stomach, leading to rapid amino acids absorption. In contrast, casein amino acids precipitate in the stomach, are released slowly in the small intestine, resulting in slower absorption. The metabolic consequences of these two kinetic profiles on the postprandial protein use have been evaluated, and it was showed that casein, a “slow-type” protein, was more efficient than its quick homologue on the postprandial protein anabolism (Boirie et al. 1997). In non-athlete subjects, in conditions of rest, whey (fast-type protein) stimulates protein synthesis, but also leucine oxidation, whereas casein (slow-type protein) does not stimulate amino acid oxidation and inhibits proteolysis. These data confirm the role played by the rate of intestinal absorption of dietary proteins, regardless of their amino acid composition.

22In the last few years, a specific attention has been paid to proteins of high-biological values co-existing in milk under the form of a complex mix. According to their superior structure, we can distinguish the micellar fraction (mainly casein proteins), and the soluble fraction (mainly whey proteins) that vary in relative proportions according to the mammal species. Cow milk contains an amount of proteins of about 30 g.l−1, comprising approximately 80% of casein and 20% of whey proteins (ratio 4:1). Whey proteins are mainly represented by ß-lactoglobulin, l’α-lactalbumin, bovine serum albumin, lactoferrin, and minor fractions among which several classes of immunoglobulins.

23Experimental studies clearly showed that milk proteins (including casein and/or whey proteins) are an important source of nitrogen components and seem more efficient than soya proteins for maximizing the rate of muscle protein synthesis during post-exercise recovery (Hartman et al. 2007; Roy, 2008). When ingested immediately after a bodybuilding exercise, whey proteins increase and prolong the activation of biological players implied in muscle hypertrophy (Hulmi et al. 2009; Kammer et al. 2009). Whey proteins specifically increase the rate of muscle protein synthesis, at rest and after resistance exercises, and to a higher extent than casein and soja proteins (Tang et al. 2009). After prolonged exercises, the consumption of low-fat milk (skimmed or semi-skimmed) as a recovery drink can be suggested; however there are only few studies devoted to examine the specific effects of such proteins on muscle growth, even though the idea seems of potential interest (Karp et al. 2006; Thomas et al. 2009). Milk consumption at the end of exercise provides both fast-and slow-dietary proteins, and ensures a high level of protein synthesis rate, at least during 6 hours (Reitelseder et al. 2010) [Fig. 6]. However, milk has been mainly studied in the context of resistance exercises, with an objective of enhancing muscle growth. Additional studies will therefore be needed before milk consumption can be unequivocally recommended during recovery from long-lasting strenuous exercises.

Figure 6: Rates of myofibrillar protein synthesis expressed as percentage per hour, over the 6 hours following a single bout of resistance exercise and intake of 0.3 g. kg-1 of either whey or casein proteins. The rate of protein synthesis was measured over the 3 hours following the end of exercise, or a further 3 hours later. Data confirm the expected effects of whey proteins on protein synthesis in the early post-exercise period, and the delayed increase in protein synthesis associated with casein proteins. Taken together, these two milk proteins ensure high levels of protein synthesis over 6 hours.

Figure 6: Rates of myofibrillar protein synthesis expressed as percentage per hour, over the 6 hours following a single bout of resistance exercise and intake of 0.3 g. kg-1 of either whey or casein proteins. The rate of protein synthesis was measured over the 3 hours following the end of exercise, or a further 3 hours later. Data confirm the expected effects of whey proteins on protein synthesis in the early post-exercise period, and the delayed increase in protein synthesis associated with casein proteins. Taken together, these two milk proteins ensure high levels of protein synthesis over 6 hours.

*: significant difference compared to the control situation (P<0.05). Adapted from Reitelseder et al. (2011).

24Associated energy intake. Maximizing the protein synthesis response to strenuous exercise requires energy quickly available in skeletal muscle. One of the major objectives of food consumption during recovery from long-lasting exercises is to quickly restore skeletal muscle glycogen levels. Therefore, the food eaten must provide a high-carbohydrate availability in order to both regenerate glycogen stores, and reduce muscle-protein breakdown via insulin, leading to improved net protein balance (Levenhagen et al. 2002). The co-ingestion of carbohydrates and proteins during recovery contributes to limit the extent and duration of muscle protein breakdown (Borsheim et al. 2004) and improves protein balance (Koopman et al. 2004).

25In conclusion, experimental data clearly show that high-intensity prolonged exercises have important consequences on the maintenance and growth of skeletal muscle mass. Some insight into the cellular and molecular mechanisms involved in the interactions between energy metabolism and muscle growth have been gleaned, but many issues remain to be examined, especially relating to the kinetics of activation and recovery of cell energy sensors. From a practical point of view, nutrition interventions are a simple way to minimize the effects of energy stress on the control of muscle mass. Current recommendations mainly rely on a regular energy intake during the event and on an adequate amount of proteins of high-biological value in combination with carbohydrates, immediately after completing exercise.

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Table des illustrations

Titre Figure 1: Schematic representation of how Akt, mTOR, and p70S6k work together to control muscle growth. This intracellular signalling pathway controls the translation of messenger RNA (mRNA) molecules – which are transcribed genes – into functional proteins.
URL http://books.openedition.org/insep/docannexe/image/1874/img-1.jpg
Fichier image/jpeg, 148k
Titre Figure 2: Relationship between the IGF-1/Akt/mTOR signalling pathway, controlling muscle protein synthesis, and the ubiquitin-proteasome pathway [atrogin-1 (MAFbx) and MuRF1], controlling muscle protein breakdown.
URL http://books.openedition.org/insep/docannexe/image/1874/img-2.jpg
Fichier image/jpeg, 80k
Titre Figure 3: Inhibitors of intracellular signalling pathways involved in muscle protein synthesis.
URL http://books.openedition.org/insep/docannexe/image/1874/img-3.jpg
Fichier image/jpeg, 68k
Titre Figure 4: Weekly changes to strength developed in the thigh extensor muscles in response to endurance (E), resistance (S) and concurrent training (S + E) programmes. Concurrent training combines both endurance and resistance exercises. Strength performances increase more slowly, and then decrease after seven weeks of concurrent training. This contrasts with the effects observed after resistance training.
Légende Adapted from Hickson et al. (1980).
URL http://books.openedition.org/insep/docannexe/image/1874/img-4.jpg
Fichier image/jpeg, 84k
Titre Figure 5: Fractional rate of protein synthesis, expressed in percentage per hour, as a function of the level of protein intake provided by food after strength exercises. Increasing dietary protein intake, up to approximately 20 g, increases the rate of protein synthesis.
Légende a, b, c: significant difference between groups (P<0.05). Adapted from Moore et al. (2009).
URL http://books.openedition.org/insep/docannexe/image/1874/img-5.jpg
Fichier image/jpeg, 20k
Titre Figure 6: Rates of myofibrillar protein synthesis expressed as percentage per hour, over the 6 hours following a single bout of resistance exercise and intake of 0.3 g. kg-1 of either whey or casein proteins. The rate of protein synthesis was measured over the 3 hours following the end of exercise, or a further 3 hours later. Data confirm the expected effects of whey proteins on protein synthesis in the early post-exercise period, and the delayed increase in protein synthesis associated with casein proteins. Taken together, these two milk proteins ensure high levels of protein synthesis over 6 hours.
Légende *: significant difference compared to the control situation (P<0.05). Adapted from Reitelseder et al. (2011).
URL http://books.openedition.org/insep/docannexe/image/1874/img-6.jpg
Fichier image/jpeg, 25k

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