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Skeletal muscle responses to unloading with special reference to man
G A Dudley1, B M Hather, P Buchanan
1Biomedical Operations and Research Office, John F. Kennedy Space Center.
The Journal of the Florida Medical Association
|August 1, 1992
Summary
Spaceflight and unloading decrease human muscle strength and mass. Earth-based models like bed rest and unilateral lower limb suspension (ULLS) effectively simulate these effects, showing significant strength loss and muscle fiber atrophy.
Area of Science:
- Human physiology
- Space medicine
- Neuromuscular adaptation
Background:
- Limited spaceflight data indicates microgravity reduces human muscle strength and mass.
- Earth-based models are crucial for studying unloading effects on the neuromuscular system due to spaceflight limitations.
Purpose of the Study:
- To investigate the impact of unloading on human neuromuscular systems using earth-based models.
- To compare the efficacy of bed rest and unilateral lower limb suspension (ULLS) in simulating spaceflight conditions.
Main Methods:
- Utilizing bed rest to eliminate lower limb weight-bearing.
- Employing unilateral lower limb suspension (ULLS) for unloading one limb during ambulatory activity.
- Analyzing muscle strength changes, particularly in the m. quadriceps femoris.
Main Results:
- Four to six weeks of bed rest, ULLS, or spaceflight caused a 20-25% decrease in m. quadriceps femoris strength.
- Muscle unloading led to a reduction in muscle fiber cross-sectional area (atrophy).
- Strength reductions were more pronounced in lower versus upper limbs and extensor versus flexor muscle groups.
Conclusions:
- Unloading induces significant adaptations in the human neuromuscular system.
- Contrary to previous beliefs, slow-twitch muscle fibers are not preferentially affected by unloading.
- Further research is needed as this field of study is still developing.