Journal Title (Medline/Pubmed accepted abbreviation): J Appl Physiol
Page numbers:834 - 845
doi (if applicable): 10.1152/japplphysiol.00949.2010
Article type: Review
Summary of article:
Skeletal muscle is remarkably malleable and is able to adapt its metabolic and functional potential in response to both external stimuli, such as exercise, and to internal modulators, such as nutrient availability. In this review, the authors examined the effect of nutrient-exercise interactions on skeletal muscle adaptations in response to both aerobic and resistance exercise. In particular, they reviewed the current understanding of molecular and cellular events that are induced in skeletal muscle in response to chronic and acute manipulation of nutrient availability. The primary nutritional modifications reviewed were the availability of carbohydrates, fats, proteins, antioxidants, and phytochemicals. The metabolic signals that are best characterized for activating energy-producing pathways are calcium release, cytoplasmic phosphorylation metabolites (ATP, ADP-Pi), and mitochondrial reduction/oxidation (redox) state of nicotinamide adenine dinucleotide (NAD/NADH). Additionally, hormones, O2 radicals, pH, and electrolyte imbalances all affect ATP synthesis and demand. The authors reported the following summary:
- Some workouts, such as short-term endurance training, when performed with low glycogen or low exogenous carbohydrate availability, augment training adaptation to a greater extent than when performed with normal glycogen stores.
- Resistance training and supplementation with proteins or amino acids stimulate muscle protein synthesis.
- Increased protein improves skeletal muscle formation.
- Initial studies suggest that antioxidants and phytochemicals are favorable nutrient supplements for skeletal muscle adaptation.
Interpretation of findings/Key practice applications:
A review of the literature affirms that acute alterations in substrate availability effectively moderate exercise response. Furthermore, when these alterations are continued, they ultimately drive the development of phenotypic characteristics common to trained athletes. It has been demonstrated that “low carbohydrate” diets may augment this capacity. However, dietary carbohydrate restriction during training has generally not resulted in enhanced exercise performance in a research testing or competitive environment. Further, lower carbohydrate diets may have a reciprocal effect on lipid availability. Diets that are “low carbohydrate” but high in fats have been linked to insulin resistance and consequent health risks. Therefore, research is still needed to better quantify carbohydrate and lipid intake and intervention periods, especially when paired with exercise, to optimize skeletal muscle adaptations. Future investigations should also focus on the timing and pattern of protein intake to identify the most appropriate and practical supplementation protocols, as well as to identify how antioxidants and phytochemicals work at the cellular level to mediate responses.
Limitations in the interpretation of study comparisons include different training modes, number of training sessions, and intervention times, as well as the multiple biologic activities that were not all assessed.