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Closed-loop, estimator-based model of human posture following reduced gravity exposure
D J Newman1, K U Schultz, J L Rochlis
1Massachusetts Institute of Technology, Cambridge 02139, USA.
Journal of Guidance, Control, and Dynamics : a Publication of the American Institute of Aeronautics and Astronautics Devoted to the Technology of Dynamics and Control
|September 1, 1996
Summary
Astronauts experience postural instability after spaceflight due to reduced muscle gains, leading to a heavy-legs sensation. This study models and experimentally verifies this phenomenon, crucial for emergency situations.
Area of Science:
- Human physiology
- Spaceflight research
- Biomechanics
Background:
- Astronauts face challenges with posture control after reduced gravity exposure.
- Postural stability is critical for astronaut safety, especially during emergency egress.
- A 'heavy legs' sensation and perceived muscular weakness are common complaints upon return to Earth's gravity.
Purpose of the Study:
- To computationally and experimentally investigate the mechanisms behind postural control deficits after reduced gravity exposure.
- To test the hypothesis that reduced muscular gains contribute to postural instability.
- To understand the physiological and biomechanical changes affecting astronaut balance.
Main Methods:
- Development of an estimator-based computational model incorporating an inverted pendulum, Hill-type muscle model, feedback pathways, and a central nervous system estimator.
- Verification of the computational model by replicating human posture's spatial and temporal characteristics.
- Experimental exposure of subjects to simulated partial gravity (3/8 g) followed by recovery exercises.
Main Results:
- Computational model results, with lowered muscle gain, supported the hypothesis of reduced muscular influence on posture.
- Experimental data showed a significant increase in the root-mean-square (rms) position of the center of pressure after reduced gravity exposure.
- Analysis revealed distinct short-term (stochastic, persistent trends) and long-term (low stochastic, antipersistent trends) postural control behaviors.
Conclusions:
- Reduced muscular gains during spaceflight are a likely cause of postural instability and the heavy-legs phenomenon upon return to 1 g.
- The developed model effectively simulates and explains postural control changes in astronauts.
- Understanding these changes is vital for developing effective countermeasures and ensuring astronaut safety.