Amino Acid Supplementation for Reversing Bed Rest and Steroid Myopathies

Abstract

Muscular inactivity is inherent in many circumstances, including convalescence from serious illness or injury, spaceflight, and the progression of aging. Inactivity in a healthy individual leads to a decrease in whole-body protein turnover composed primarily of a decrease in muscle protein synthesis. The decrease in muscle protein synthesis leads to a substantial loss of lean body mass. We have demonstrated that this loss of lean mass is greater when inactivity is accompanied by stress, specifically hypercortisolemia. During convalescence from trauma or injury, the anabolic stimulus provided by nutrient ingestion represents a primary means of ameliorating the loss of muscle protein. We have previously demonstrated that ingestion of essential amino acids (EAAs), formulated to mimic the proportion of EAAs in muscle, provides a potent anabolic stimulus for muscle protein. Recently, we demonstrated that EAA supplementation throughout 28 d of bed rest stimulated net muscle protein synthesis. The repeated stimulation translated to maintenance of lean body mass and an amelioration of functional decrement compared to a placebo treatment. We have also demonstrated that this EAA supplement stimulates net protein synthesis during acute hypercortisolemia and are currently testing the effects during prolonged inactivity. Although EAAs promote muscle anabolism during hypercortisolemia, it is unlikely that a nutritional intervention alone would be effective in maintaining lean body mass during severe stress. It may be necessary to concomitantly reduce the catabolic influence of cortisol or provide another anabolic stimulus.