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1 Department of Physiology and
Pharmacology,
Received 1 May 1996; accepted in final form 12 September 1996.
Berg, H. E., L. Larsson, and P. A. Tesch. Lower limb
skeletal muscle function after 6 wk of bed rest. J. Appl. Physiol. 82(1): 182-188, 1997.
atrophy; electromyography; humans; inactivity; maximum voluntary
strength
Force,
electromyographic (EMG) activity, muscle mass, and fiber
characteristics were studied in seven healthy men before and after 6 wk
of bed rest. Maximum voluntary isometric and concentric knee extensor
torque decreased (P < 0.05)
uniformly across angular velocities by 25-30% after bed rest.
Maximum quadricep rectified EMG decreased by 19 ± 23%, whereas
submaximum (100-Nm isometric action) EMG increased by 44 ± 28%.
Knee extensor muscle cross-sectional area (CSA), assessed by using
magnetic resonance imaging, 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
percentages nor their relative proportions of myosin heavy chain (MHC)
isoforms were altered after bed rest. Because the decline in strength
could not be entirely 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 MHC composition or in vivo
muscle contractile properties.
0161-7567/97 $5.00
Copyright © 1997 the American Physiological Society
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