Lower limb skeletal muscle function after 6 weeks of bedrest.
Berg, H. E., L. Larsson, and P. A. Tesch.
Department of Physiology and Pharmacology, Karolinska Institute and
Department of Clinical Neurophysiology, Karolinska Hospital,
Stockholm, Sweden
APStracts 3:0446A, 1996.
Force, electromyographic (EMG) activity, muscle mass and fiber
characteristics were studied in 7 healthy males before and after 6 wk
bedrest. Maximum voluntary isometric and concentric knee extensor
torque decreased (p<0.05), uniformly across angular
velocities, by 25-30% after bedrest. Maximum quadricep rectified EMG
decreased by 19+/-23% while submaximum (100Nm isometric action) EMG
increased by 44+/-28%. Knee extensor muscle cross-sectional area
(CSA), assessed using magnetic resonance imaging (MRI), decreased by
14+/-4%. Maximum torque per knee extensor CSA decreased by 13+/-9%.
Vastus lateralis fiber CSA decreased 18+/-14%. Neither type I, IIA
and IIB fiber percentage nor their relative proportion of myosin
heavy chain (MyHC) isoforms were altered after bedrest. Because the
decline in strength could not entirely be accounted for by decreased
muscle CSA, it is suggested that the strength loss is also due to
factors resulting in decreased neural input to muscle and/or reduced
specific tension of muscle as evidenced by a decreased torque/EMG
ratio. Additionally, it is concluded that muscle unloading in humans
does not induce important changes in fiber type or MyHC composition
or in vivo muscle contractile properties.
Received 1 May 1996; accepted in final form 12 September 1996.
APS Manuscript Number A419-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996