title: The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation.
abstract: 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 (muN.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.
authors.affiliation: Dept. of Biology, Marquette University, Wehr Life Sciences Bldg., PO Box 1881, Milwaukee, WI 53201-1881, USA. robert.fitts@mu.edu
authors.forename: R H
authors.initials: RH
authors.lastname: Fitts
authors.forename: J G
authors.initials: JG
authors.lastname: Romatowski
authors.forename: J R
authors.initials: JR
authors.lastname: Peters
authors.forename: D
authors.initials: D
authors.lastname: Paddon-Jones
authors.forename: R R
authors.initials: RR
authors.lastname: Wolfe
authors.forename: A A
authors.initials: AA
authors.lastname: Ferrando
mesh_terms: D000328:Adult; D000601:Amino Acids, Essential / Q000008:administration & dosage*; D001510:Bed Rest / Q000009:adverse effects*; D002908:Chronic Disease; D003480:Cushing Syndrome / Q000139:chemically induced / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D019422:Dietary Sucrose / Q000008:administration & dosage*; D006801:Humans; D006854:Hydrocortisone / Q000031:analogs & derivatives; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000473:pathology; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000473:pathology; D053580:Muscle Strength / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D009133:Muscular Atrophy / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000601:Amino Acids, Essential; D019422:Dietary Sucrose; C007133:hydrocortisone hemisuccinate; D006854:Hydrocortisone