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Skeletal muscle responses to unloading with special reference to manThe limited space flight data suggest that exposure to microgravity decreases muscle strength in humans and muscle mass in lower mammals. Several earth-based models have been used to address the effect of unloading on the human neuromuscular system due to the limited access of biological research to long-term space flight. Bedrest eliminates body weight bearing of both lower limbs. Unilateral lower limb suspension (ULLS), where all ambulatory activity is performed on crutches with an elevated sole on the shoe of one foot, has recently been used to unload one lower limb. The results from studies using these two models support their efficacy. The decrease in strength of m. quadriceps femoris, for example, after four to six weeks of bedrest, ULLS or space flight is 20 to 25 percent. The results from the earth-based studies show that this response can be attributed in part to a decrease in the cross-sectional area of the KE which reflects muscle fiber atrophy. The results from the ground based studies also support the limited flight data and show that reductions in strength are larger in lower than upper limbs and in extensor than flexor muscle groups. They also raise issue with the generally held concept that postural muscle is most affected by unweighting. Slow-twitch fibers in lower limb muscles of mixed fiber type composition and muscle composed mainly of slow-twitch fibers do not preferentially atrophy after bedrest or ULLS. Taken together, the data suggest that unloading causes remarkable adaptations in the neuromuscular system of humans. It should be appreciated, however, that this area of research is in its infancy.
Document ID
19930044721
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Dudley, G. A.
(NASA John F. Kennedy Space Center Cocoa Beach, FL, United States)
Hather, B. M.
(NASA John F. Kennedy Space Center Cocoa Beach, FL, United States)
Buchanan, P.
(NASA Kennedy Space Center Cocoa Beach, FL, United States)
Date Acquired
August 16, 2013
Publication Date
August 1, 1992
Publication Information
Publication: Florida Medical Association, Journal
Volume: 79
Issue: 8
ISSN: 0015-4148
Subject Category
Aerospace Medicine
Accession Number
93A28718
Distribution Limits
Public
Copyright
Other

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