Skeletal muscle responses to lower limb suspension in humans.
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)
Hather
B M
BM
Biomedical and Environmental Laboratories, Bionetics Corporation, Kennedy Space Center 32899, Melbourne, Florida.
Adams
G R
GR
Tesch
P A
PA
Dudley
G A
GA
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000328:Adult; D002196:Capillaries / Q000473:pathology; D005260:Female; D006801:Humans; D007866:Leg; D008279:Magnetic Resonance Imaging; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000378:metabolism / Q000473:pathology*; D009133:Muscular Atrophy / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D010503:Periodic Acid-Schiff Reaction; D014893:Weightlessness / Q000009:adverse effects*
D000251:Adenosine Triphosphatases