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Biomechanical Research in Space
Gideon B. Ariel, Ph.D.


Biomechanics is fundamental to understanding the work performance capabilities of humans in space. Biomechanics as practiced by NASA has the primary goal of conducting operationally-oriented research focusing on maximizing astronaut on-orbit performance capabilities. One immediate and important objective of this research is to minimize the effects of deconditioning during spaceflight using individualized exercise "prescriptions" and in-flight exercise facilities combined with extensive biomechanical analysis of movement in micro-gravity. Results from experiments on the Gemini, Apollo, and Skylab missions suggest that regular exercise is helpful in minimizing several aspects of spaceflight deconditioning (1,2,3). In fact, exercise is the only countermeasure that can potentially counteract the combined cardiovascular, musculoskeletal and neuromuscular effects of adaptation. One of the ways the human body reacts to the reduced physiological and mechanical demands of micro-gravity is by a deconditioning of the cardiovascular, musculoskeletal, and neuromuscular systems. Deconditioning produces a multitude of physical changes such as loss of muscle mass, decreases in bone density and body calcium. It is also responsible for decreased muscle performance, strength and endurance, orthostatic intolerance, and overall decreases in aerobic and anaerobic fitness. Deconditioning presents operational problems during spaceflight and upon return to I-G. Muscular and cardiovascular deconditioning contributes to decreased work capacity during physically demanding extravehicular activities (EVAs); neuromuscular and perceptual changes precipitate alterations in magnitude estimation, or the so-called "input-offset" phenomenon; and finally, decreased vascular compliance can lead to syncopal episodes upon re-entry and landing. Extravehicular activity is the most physically demanding task that astronauts perform on-orbit. Space Station Freedom and manned Lunar and Mars missions will greatly increase the number, frequency, and complexity of EVA's within the next 10 to 20 years.

The purpose of our biomechanical analysis in space is to provide a program of exercise countermeasures that will minimize the operational consequences of microgravity-induced deconditioning by providing individualized exercise 'prescriptions' for each crew member. Task requirements have been defined in terms of the musculoskeletal and neuromuscular system demands induced by microgravity, and training protocols developed to address deconditioning in these systems to serve as the basis for training prescriptions. To achieve these training protocols it was necessary to develop flight exercise hardware and associated software related to biomechanical measurement devices.


Some of the critical issues that had to be addressed in order to achieve the above goals were:

  1. What type of exercise devices such as weight training, bicycling, rowing, swimming, running, etc. are necessary to train all of the organ systems affected by deconditioning?
  2. Which indices are the most reliable indicators of changes in fitness?
  3. Which reliable indicators of changes in fitness best describe the changes caused by deconditioning?
  4. How does training in micro-gravity differ from training in 1-G ?
  5. What are the differences between training that includes impact forces and training that uses non-impact forces?
  6. Can an artificial intelligence expert system be developed to aid in monitoring, controlling, and adjusting prescriptions?

Next, an exercise dynamometer had to be designed for exercise purposes that could also analyse muscle functions and efficiencies. Some of the requirements of such an in-flight O-G exercise dynamometer were:

  1. The flexibility of performing exercises and diagnostics in isotonic, isokinetic, isometric, accommodating velocity at variable loads as well as accommodating resistance at variable speeds, or any combination of these exercise controlled modes.
  2. The ability to perform exercises and diagnostics from a pre-programmed sequence of tests and exercises stored on computer disk. The investigators needed to be able to prescribe for object, testing and rehabilitation programs from a library of specialized programs or be able to create specific protocols tailored for a particular subject.
  3. To offer user-friendly, menu-driven software packages which would be easy learned and are simple to operate.
  4. To allow for data transfer to other commercial or custom software packages for extraordinary graphing, data report formats, statistical analysis, etc.
  5. Allow for external analog data acquisition that could be correlated with the acquired force curves such as electromyographic and load cell data.

Such a system has been developed by the author and its utilization in a micro-gravity environment shows great promise.


  1. Thornton, W. et al. In: Biomedical Results From Skylab, Chapter 21, NASA, 1977.
  2. Johnson, R.S. In: Biomedical Results From Skylab, Chapter 1, NASA, 1977.
  3. Moore, T.P. Proceedings of NASA Sponsored Workshop On Exercise Prescription For Long-Duration Space Flight, Houston, Texas, 1989.



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