Journal Title (Medline/Pubmed accepted abbreviation): J Sports Sci Med
Page numbers: 354-363
Article type: Review
This review discusses the effects of protein and carbohydrate intake during postexercise recovery on muscle protein and glycogen synthesis. Studies have shown that both protein breakdown and synthesis are elevated from baseline following resistance training. However, protein breakdown rates exceed synthesis, thus resulting in a negative protein balance. Protein or amino acid intake following exercise has been shown to increase protein synthesis while breakdown rates are unaffected. Consequently, a positive protein balance is achieved, with a potential for skeletal muscle hypertrophy. Protein supplementation immediately following exercise more effectively induces muscle hypertrophy compared with later supplementation times.
In contrast, carbohydrates alone have a minimal effect on net protein balance during exercise recovery. Carbohydrates are, however, necessary for glycogen synthesis following exercise, which replenishes energy stores and aids in recovery. Because glycogen synthesis occurs in 2 phases (rapid [30-60 minutes, insulin not required], and slow [several hours, requires insulin]), timing of carbohydrate intake was hypothesized to influence glycogen synthesis. However, studies evaluating carbohydrate ingestion times following exercise have yielded mixed results, possibly due to limitations such as the amount and composition of the carbohydrates, as well as the fitness levels of the study populations. Studies evaluating carbohydrate types (sucrose, fructose, and glucose) have also reported mixed results, although ingesting a solid versus a liquid meal provided similar glycogen synthesis rates. Increasing carbohydrate ingestion has been shown to increase glycogen synthesis up to a maximum rate, while the addition of protein to carbohydrates has only increased glycogen synthesis under certain conditions (eg, insufficient carbohydrate availability).
Protein or amino acid intake following exercise is proven to effectively increase protein synthesis rates. However, it is unnecessary to combine amino acids with protein if the amount of protein intake is adequate. If glycogen stores need to be replenished quickly, the authors recommend that athletes ingest carbohydrates immediately or soon after completing a prolonged or high-intensity bout of exercise. If long-term maintenance of carbohydrate stores is the goal, however, then a daily intake of more than 8 g/kg/day is recommended. Studies support carbohydrate intake above 0.35 g/kg/hr to increase glycogen synthesis, with 1.2 g/kg/hour as optimal for achieving maximum glycogen synthesis.