Abstract
Eight subjects participated in a 6-wk unilateral lower limb suspension (ULLS) study to determine the influence of reduced weight bearing on human skeletal muscle morphology. The right shoe was outfitted with a platform sole that prevented the left foot from bearing weight while walking with crutches, yet it allowed freedom of movement about the ankle, knee, and hip. Magnetic resonance images pre- and post-ULLS showed that thigh muscle cross-sectional area (CSA) decreased (P less than 0.05) 12% in the suspended left lower limb, whereas right thigh muscle CSA did not change. Likewise, magnetic resonance images collected post-ULLS showed that muscle CSA was 14% smaller (P less than 0.05) in the left than in the right leg. The decrease in muscle CSA of the thigh was due to a twofold greater response of the knee extensors (-16%, P less than 0.05) than knee flexors (-7%, P less than 0.05). The rectus femoris muscle of the knee extensors showed no change in CSA, whereas the three vastus muscles showed similar decreases of approximately 16% (P less than 0.05). The apparent atrophy in the leg was due mainly to reductions in CSA of the soleus (-17%) and gastrocnemius muscles (-26%). Biopsies of the left vastus lateralis pre- and post-ULLS showed a 14% decrease (P less than 0.05) in average fiber CSA. The decrease was evident in both type I (-12%) and II (-15%) fibers. The number of capillaries surrounding the different fiber types was unchanged after ULLS.(ABSTRACT TRUNCATED AT 250 WORDS)
Highlights
Physiol. 72(4): 1493-1498, 1992.-Eight subjects participated in a 6-wk unilateral lower limb suspension (ULLS) study to determine the influence of reduced weight bearing on human skeletal muscle morphology
Decreases (P < 0.05) in cross-sectional area (CSA) of both the images were not collected for the leg before or on day 26 knee flexor and knee extensor muscle groups contributed of ULLS because of limited availability of the imager. to the reduction in thigh muscle CSA (Table 1)
The purpose of the present study was to examine the influence of the loss of body weight bearing on skeletal muscle morphology of the lower limb in healthy humans
Summary
Magnetic resonance images pre- and post-ULLS showed that thigh muscle cross-sectional area (CSA) decreased skeletal muscle CSA after 4 wk of bed rest and the approximate 20% reduction in knee extensor strength after 4 or 5 wk of bed rest or 4 wk of spaceflight (4, 9, 12, 27). Taken together, these results suggestthatlowerlimb suspension in humans induces neuromuscular responses to unweighting, comparable to spaceflight and the more constrained 1-G model, bed rest. Biopsies of the left vastus lateralis pre- and post- may explain the larger reduction in knee extensor
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