COLUMNS: Nutrition and Ergogenic Aids
Heavy resistance training changes the balance of muscle protein turnover leading to gains in skeletal muscle mass (6). The role of nutrition in affecting the adaptive response of skeletal muscle to heavy resistance training has been examined by several investigators. It has been posited that the provision of protein and amino acids is the key nutrient regulator of skeletal muscle protein turnover and subsequent skeletal muscle fiber hypertrophy. During exercise, muscle protein synthesis decreases together with a net increase in protein degradation and stimulation of branched-chain amino acid (BCAA) oxidation (the BCAAs are leucine, valine, and isoleucine). After exercise, recovery of muscle protein synthesis requires dietary protein or BCAAs. Thus, both insulin and leucine allow skeletal muscle to coordinate protein synthesis post-exercise upon the consumption of proper nutrients (4,5). However, in addition to the data showing that the acute response to combined heavy resistance exercise and nutrient ingestion (i.e., protein and amino acids) promotes skeletal muscle protein accretion (7–9), there are longitudinal studies that show improvements in body composition and exercise performance as a result of proper supplementation.
For instance, a recent study examined 10 weeks of resistance training and the ingestion of supplemental protein and amino acids on muscle performance and markers of muscle anabolism. Nineteen untrained males were randomly assigned to supplement groups containing either 20-g protein or 20-g dextrose placebo ingested 1 hour before and after exercise for a total of 40 g/d. The total pre- and post-serving of protein was as follows: 14-g whey protein concentrate, 6-g whey protein isolate, 4-g milk protein isolate, 4-g calcium caseinate, and 12-g free amino acids (0.22-g arginine, 0.22-g histidine, 0.14-g isoleucine, 6.0-g leucine, 0.44-g lysine, 0.44-g methionine, 0.20-g phenylalanine, 0.22-g valine, 0.12-g aspartate, 2.0-g glutamine, and 2.0-g tyrosine). Subjects exercised 4 times per week using 3 sets of 6–8 repetitions at 85–90% of the 1RM. Compared to carbohydrate supplementation, consuming the combination of protein and amino acids resulted in greater increases in total body mass, fat-free mass, thigh mass, muscle strength, serum IGF-1, IGF-1 mRNA, MHC I and IIa expression, and myofibrillar protein. In fact, the protein group experienced a mean increase of 5.6-kg of fat-free mass compared to the 2.7-kg gain in the carbohydrate group. More importantly, myofibrillar protein content was elevated by 45% in the protein-supplemented group versus 18% in the carbohydrate group. It is clear that within the parameters of this particular investigation, 10 weeks of resistance training combined with 20-g protein and amino acids ingested 1 hour before and after exercise is more effective than carbohydrate placebo in up-regulating markers of muscle protein synthesis and anabolism along with subsequent improvements in muscle performance (10).
There are other investigations that support the findings by Willoughby et al. (10) that demonstrate that the consumption of carbohydrate alone does not promote optimal gains in muscle protein. Andersen et al. (1) compared the effects of 14 weeks of resistance training combined with timed ingestion of isoenergetic protein versus carbohydrate supplementation on muscle fiber hypertrophy and mechanical muscle performance. Supplementation was administered before and immediately after each training bout and, in addition, in the morning on nontraining days. After 14-weeks of resistance training, the protein group demonstrated statistically significant hypertrophy of type I (+18%) and type II (+26%) muscle fibers, whereas no change above baseline occurred in the carbohydrate group. Squat jump height increased only in the protein group, whereas countermovement jump height and peak torque during slow isokinetic muscle contraction increased similarly in both groups (1). Additionally, Bird et al. (2) examined 32 untrained young men who performed 12-weeks of resistance training twice weekly, consuming ∼675-mL of either a 6% carbohydrate (CHO) solution, 6-g essential amino acid (EAA) mixture, combined CHO + EAA supplement, or placebo (PLA). Muscle fiber cross-sectional area increased across groups for type I, IIa, and IIx fibers; however, the CHO + EAA had the greatest gains in muscle fiber cross-sectional area relative to PLA (P < 0.05). This study indicates that CHO + EAA ingestion enhances muscle anabolism following resistance training to a greater extent than either CHO or EAA consumed independently. It is posited that the synergistic effect of CHO + EAA ingestion maximizes the anabolic response presumably by attenuating the postexercise increase in protein degradation (2).
CONCLUSION AND PRACTICAL APPLICATIONS
Protein and amino acid supplementation before and after exercise have been shown to promote gains in skeletal muscle mass, muscle fiber cross-sectional area, or myofibrillar protein to a greater extent than carbohydrate alone. This supports the acute data that demonstrate that the ingestion of carbohydrates on net leg protein balance after resistance exercise is minor compared to the effect of EAA consumption (3). Consuming a combination of carbohydrate and protein/amino acid may be optimal for promoting skeletal muscle protein accretion. The mechanism for this may be related in part to the elevation of serum insulin and perhaps the up-regulation of IGF-1. However, Willoughby et al. (10) showed that the protein and amino acid supplement was shown to have a more pronounced effect on markers of skeletal muscle anabolism when compared to a carbohydrate PLA, despite a less pronounced serum insulin response. This may have been due to the added free amino acids, particularly leucine, where cooperatively with insulin and IGF-1 signaling may have further promoted skeletal muscle protein synthesis. The cellular mechanisms governing the role of nutrients in affecting skeletal muscle protein accretion are not entirely understood. From a practical standpoint, it is evident that in order to maximize gains in skeletal muscle mass and perhaps improve performance, the consumption and timing of a protein- or amino acid–based food or supplement may be warranted. Furthermore, the existing data suggest that carbohydrate alone is insufficient for promoting an anabolic response.▪
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