The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation

• Published in: American Journal of Physiology: Cell Physiology Vol. 293; no. 1; pp. C313 - C320
• Main Authors: Fitts, R. H, Romatowski, J. G, Peters, J. R, Paddon-Jones, D, Wolfe, R. R, Ferrando, A. A
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.07.2007
• Subjects: Adult; Amino acids; Amino Acids, Essential - administration & dosage; Bed Rest - adverse effects; Blood diseases; Carbohydrates; Chronic Disease; Cushing Syndrome - chemically induced; Cushing Syndrome - complications; Cushing Syndrome - pathology; Cushing Syndrome - physiopathology; Diet; Dietary Sucrose - administration & dosage; Humans; Hydrocortisone - analogs & derivatives; Male; Muscle Contraction - drug effects; Muscle Fibers, Fast-Twitch - drug effects; Muscle Fibers, Fast-Twitch - pathology; Muscle Fibers, Slow-Twitch - drug effects; Muscle Fibers, Slow-Twitch - pathology; Muscle Strength - drug effects; Muscle, Skeletal - drug effects; Muscle, Skeletal - pathology; Muscle, Skeletal - physiopathology; Muscular Atrophy - etiology; Muscular Atrophy - pathology; Muscular Atrophy - physiopathology; Muscular Atrophy - prevention & control; Musculoskeletal system; Time Factors; Treatment Outcome
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00573.2006

1 Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin; and 2 Department of Surgery, The University of Texas Medical Branch, and Shriners Hospitals for Children, Galveston, Texas Submitted 10 November 2006 ; accepted in final form 27 March 2007 Prolonged inactivity associated with bed rest in a clinical setting or spaceflight is frequently associated with hypercortisolemia and inadequate caloric intake. Here, we determined the effect of 28 days of bed rest (BR); bed rest plus hypercortisolemia (BRHC); and bed rest plus essential amino acid (AA) and carbohydrate (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 prevalue 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 vastus lateralis (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. isotonic contractile properties; peak force and power; calcium sensitivity; essential amino acids Address for reprint requests and other correspondence: R. H. Fitts, Marquette Univ., Dept. of Biology, Wehr Life Sciences Bldg., PO Box 1881, Milwaukee, WI 53201-1881 (e-mail: robert.fitts{at}mu.edu )