The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation
To investigate the adverse effects of 28 days of bed rest plus hypercortisolemia on muscle fiber function and force, as well as the potential for an essential amino acid and carbohydrate supplement to protect against muscle atrophy and functional loss of individual slow- and fast-twitch fibers of ankle (soleus) and knee (VL) extensors.
All participants were assigned to 28 days of bed rest and then separated into 3 groups: bed rest only, bed rest plus hypercortisolemia, and bed rest plus supplementation with an essential amino acid and carbohydrate supplement.
Results showed that high levels of cortisol made the muscle atrophy and functional decline of soleus type I fibers worse, as expected. The loss of force in single fibers and the muscle atrophy in hypercortisolemia subjects were 2 to 3 times greater in the ankle than in the knee extensors.
Findings also indicate that supplementation with essential amino acids + carbohydrate protected against a decrease in soleus type I fiber force and prevented a loss in the peak power of the VL type II fibers.
An essential amino acid plus carbohydrate supplement can help preserve single fiber function during long-term bed rest and spaceflight likely due to the ability to increase muscle protein synthesis. Researchers conclude that supplementation with essential amino acids can help stimulate muscle protein synthesis and thus protect against microgravity-induced loss of myofibrillar protein, muscle atrophy, and decrease in fiber force and power.
Inadequate nutrition and caloric intake exacerbate the loss of muscle mass and strength experienced by astronauts on long space missions and patients prescribed extended bed rest. An essential amino acid supplement with appropriate carbohydrate support can help astronauts and patients meet their nutritional needs and maintain muscle mass, strength, and function.
Fitts RH, Romatowski JG, Peters JR, Paddon-Jones D, Wolfe RR, Ferrando AA. The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation. Am J Physiol Cell Physiol. 2007 Jul;293(1):C313-20. Epub 2007 Apr 4. PMID:17409123