Protein intake and muscle mass
AX Bigarda, *
a Unité de bioénergétique, centre de recherches du service de santé des Armées 38702 La Tronche cedex France
Reçu le: 30 Juin 1996; accepté le: 15 Octobre 1996. Available online 26 May 1999.
Abstract
There is a general belief among strength-trained athletes that high-protein intakes have a positive effect on muscle mass accretion and lead to greater strength gains. There is now substantive evidence indicating that protein intakes above the current recommended dietary allowance (0.8 g·kg-1·day-1) are needed to maintain positive nitrogen balance. Restricted energy intake in an attempt to reduce body weight to make a particular weight class, results in increase in protein needs. For strength athletes, protein intakes of 1.6 to 2 g·kg-1·day-1 are close to the optimal requirements for muscle development. There is now experimental evidence that excessive protein intake compared with adequate intake does not result in an increased muscle protein synthesis. Amino acids deriving from excess protein intake are oxidized rather than stored as protein. Thus, there is no data available to date, showing that protein intakes as high as 3-4 g·kg-1·day-1 have positive effects on muscle mass development. Gains in muscle mass are likely influenced not only by the volume and intensity of exercise during training, but also by the hormonal environment of the muscles. It has been hypothesized that amino acid supplements can influence the hormonal milieu during and after strength exercise and promote skeletal muscle anabolism. There is only little scientific evidence supporting the hypothesis that specific amino acid supplements may stimulate growth hormone (GH) release. It is likely that the magnitude of GH production consequent to heavy-resistance exercise might be higher than GH release resulting from amino acid intake. However, carbohydrate-protein supplements can affect the anabolic hormonal milieu after exercise, and are able to stimulate an environment favorable for muscle growth by increasing plasma concentrations of GH and insulin. Thus, while it is important to maintain protein balance during strength training, amino acids consumed in excess do not result in an increased accretion of lean body mass.
Résumé
Il est un principe acquis par tous les pratiquants de sports de force, que l'enrichissement de la ration en protéines est un facteur d'amélioration des performances. Une revue des données de la littérature permet de confirmer que l'équilibre de la balance azotée d'athlètes pratiquant régulièrement des sports de force, nécessite un apport de protéines supérieur aux normes minimales recommandées (0,8 g·kg-1·j-1). Les restrictions d'apport énergétique, souvent imposées pour respecter des catégories de poids en compétition, ne font qu'augmenter les besoins en protéines. Chez les sujets entraînés, 1,6 à 2 g·kg-1·j-1 de protéines alimentaires représentent probablement l'apport optimal pour le développement de la masse musculaire. Les apports massifs couramment réalisés ne peuvent conduire qu'à uneé limination des acides aminés apportés en excès et il est bien difficile de justifier scientifiquement des apports aussi importants. L'ingestion d'acides aminés spécifiques a été proposée, dans le but de moduler le statut hormonal des sujets. Actuellement, il n'existe pas de consensus permettant de confirmer les effets chez l'homme, de l'ingestion de doses importantes de certains acides aminés sur la production de GH.
C'è ANCHE IL FANCè PER MISTER x
AX Bigarda, *
a Unité de bioénergétique, centre de recherches du service de santé des Armées 38702 La Tronche cedex France
Reçu le: 30 Juin 1996; accepté le: 15 Octobre 1996. Available online 26 May 1999.
Abstract
There is a general belief among strength-trained athletes that high-protein intakes have a positive effect on muscle mass accretion and lead to greater strength gains. There is now substantive evidence indicating that protein intakes above the current recommended dietary allowance (0.8 g·kg-1·day-1) are needed to maintain positive nitrogen balance. Restricted energy intake in an attempt to reduce body weight to make a particular weight class, results in increase in protein needs. For strength athletes, protein intakes of 1.6 to 2 g·kg-1·day-1 are close to the optimal requirements for muscle development. There is now experimental evidence that excessive protein intake compared with adequate intake does not result in an increased muscle protein synthesis. Amino acids deriving from excess protein intake are oxidized rather than stored as protein. Thus, there is no data available to date, showing that protein intakes as high as 3-4 g·kg-1·day-1 have positive effects on muscle mass development. Gains in muscle mass are likely influenced not only by the volume and intensity of exercise during training, but also by the hormonal environment of the muscles. It has been hypothesized that amino acid supplements can influence the hormonal milieu during and after strength exercise and promote skeletal muscle anabolism. There is only little scientific evidence supporting the hypothesis that specific amino acid supplements may stimulate growth hormone (GH) release. It is likely that the magnitude of GH production consequent to heavy-resistance exercise might be higher than GH release resulting from amino acid intake. However, carbohydrate-protein supplements can affect the anabolic hormonal milieu after exercise, and are able to stimulate an environment favorable for muscle growth by increasing plasma concentrations of GH and insulin. Thus, while it is important to maintain protein balance during strength training, amino acids consumed in excess do not result in an increased accretion of lean body mass.
Résumé
Il est un principe acquis par tous les pratiquants de sports de force, que l'enrichissement de la ration en protéines est un facteur d'amélioration des performances. Une revue des données de la littérature permet de confirmer que l'équilibre de la balance azotée d'athlètes pratiquant régulièrement des sports de force, nécessite un apport de protéines supérieur aux normes minimales recommandées (0,8 g·kg-1·j-1). Les restrictions d'apport énergétique, souvent imposées pour respecter des catégories de poids en compétition, ne font qu'augmenter les besoins en protéines. Chez les sujets entraînés, 1,6 à 2 g·kg-1·j-1 de protéines alimentaires représentent probablement l'apport optimal pour le développement de la masse musculaire. Les apports massifs couramment réalisés ne peuvent conduire qu'à uneé limination des acides aminés apportés en excès et il est bien difficile de justifier scientifiquement des apports aussi importants. L'ingestion d'acides aminés spécifiques a été proposée, dans le but de moduler le statut hormonal des sujets. Actuellement, il n'existe pas de consensus permettant de confirmer les effets chez l'homme, de l'ingestion de doses importantes de certains acides aminés sur la production de GH.
C'è ANCHE IL FANCè PER MISTER x
