Abstract
Unloaded inactivity induces atrophy and functional deconditioning of skeletal muscle, especially in the lower extremities. Information is scarce, however, regarding the effect of unloaded inactivity on muscle size and function about the hip. Regional bone loss has been demonstrated in hips and knees of elderly orthopaedic patients, as quantified by computerized tomography (CT). This method remains to be validated in healthy individuals rendered inactive, including real or simulated weightlessness. In this study, ten healthy males were subjected to 5 weeks of experimental bedrest and five matched individuals served as ambulatory controls. Maximum voluntary isometric hip and knee extension force were measured using the strain gauge technique. Cross-sectional area (CSA) of hip, thigh and calf muscles, and radiological density (RD) of the proximal tibial bone were measured using CT. Bedrest decreased (P < 0.05) average (SD) muscle strength by 20 (8)% in knee extension, and by 22 (12)% in hip extension. Bedrest induced atrophy (P < 0.05) of extensor muscles in the gluteal region, thigh and calf, ranging from 2 to 12%. Atrophy was more pronounced in the knee extensors [9 (4)%] and ankle plantar flexors [12 (3)%] than in the gluteal extensor muscles [2 (2)%]. Bone density of the proximal tibia decreased (P < 0.05) by 3 (2)% during bedrest. Control subjects did not show any temporal changes in muscle or bone indices (P > 0.05), when examined at similar time intervals. The present findings of a substantial loss in hip extensor strength and a smaller, yet significant atrophy of these muscles, demonstrate that hip muscle deconditioning accompanies losses in thigh and calf muscle mass after bedrest. This suggests that comprehensive quantitative studies on impaired locomotor function after inactivity should include all joints of the lower extremity. Our results also demonstrate that a decreased RD, indicating bone mineral loss, can be shown already after 5 weeks of unloaded bedrest, using a standard CT technique.
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Acknowledgments
The support of the personnel at the Valdoltra Orthopaedic Hospital in Ankaran (Slovenia) is gratefully acknowledged, particularly that of Prim. dr. Vencesalv Pisot (Director) and Mrs. Stanislava Skrabec (Head Nurse). The study was supported, in part, by grants from the Swedish Defence Research Agency, the Slovene Ministry of Education, Science and Sport, Orthopedic Hospital Valdoltra, and the Jozef Stefan Institute to the principal investigators Ola Eiken and Igor B Mekjavic. The authors are particularly grateful to Anders Brumer and Jon-Arne Reitan for their assistance in the data analysis, and for providing physiotherapy during the bedrest portion of the study. Thanks also to Dr. Alan Kacin who assisted with the physiotherapy during the study and supervised the active recovery period.
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Berg, H.E., Eiken, O., Miklavcic, L. et al. Hip, thigh and calf muscle atrophy and bone loss after 5-week bedrest inactivity. Eur J Appl Physiol 99, 283–289 (2007). https://doi.org/10.1007/s00421-006-0346-y
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DOI: https://doi.org/10.1007/s00421-006-0346-y