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1 Biological Sciences, Marquette University, Milwaukee, Wisconsin, United States
2 Milwaukee, Wisconsin, United States; Biological Sciences, Marquette University, United States
3 Surgery, University of Texas Medical Branch, Galveston, Texas, United States
4 Geriatrics, University of Arkansas Medical School, Little Rock, Arkansas, United States
5 Little Rock, Arkansas, United States; Geriatrics, University of Arkansas Medical School, Little Rock, Arkansas, United States
* To whom correspondence should be addressed. E-mail: robert.fitts{at}mu.edu.
Prolonged inactivity associated with bed rest in a clinical setting or space fight is frequently associated with hypercortisolemia and inadequate caloric intake. Here, we determined the effect of 28 d of bed rest (BR); bed rest plus hypercortisolemia (BRHC); and bed rest plus essential amino acid and carbohydrate (AA/CHO) supplement (BRAA) on the size and function of single slow- and fast-twitch muscle fibers. Supplementing meals, the BRAA group consumed 16.5 g essential amino acids and 30 g sucrose at 1100, 1600, and 2100 h, and the BRHC subjects received 5 daily doses of 10-15 mg of oral hydrocortisone sodium succinate throughout bed rest. Bed rest induced atrophy and loss of force (mN) and power (µN·FL·s-1) in single fibers was exacerbated by hypercortisolemia where soleus peak force declined by 23% in the type I fiber from a pre value of 0.78 ± 0.02 to 0.60 ± 0.02 mN post bed rest (compared to a 7% decline with bed rest alone) and 27% in the type II fiber (1.10 ± 0.08 vs. 0.81 ± 0.05 mN). In the BRHC group, Peak power dropped by 19, 15, and 11 % in the soleus type I, and VL type I and II fibers, respectively. The AA/CHO supplement protected against the bed rest-induced loss of peak force in the type I soleus and peak power in the VL type II fibers. These results provide evidence that an AA/CHO supplement might serve as a successful countermeasure to help preserve muscle function during periods of relative inactivity.
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