Biomechanical Countermeasures to Space Flight- Induced Osteoporosis
A. Introduction
Exercise in microgravity is one of the most promising countermeasures to the dual problems of space flight-induced bone loss and muscle atrophy. Although exercise in microgravity has been studied extensively from a metabolic standpoint, little research has focused on the efficacy of different forms of exercise for maintaining musculoskeletal integrity in this unique environment. Exercise protocols thus far have not been effective in preventing muscle atrophy and bone loss during space flight, especially in the lower extremities. In 1-G, however, animal experiments have clearly indicated that certain bone strains and strain rates do stimulate bone deposition, and repetitive loading of the lower extremity can increase osteonal bone formation even as proximally as the vertebral column. Such studies have also indicated that a relatively small number of appropriate loading cycles may lead to bone deposition. This suggests that an optimal exercise regimen might be able to maintain bone and muscle integrity during space flight.
The major aims of the study are:
- To determine the relationship between externally applied impact loads and ratesof loading and the (global) strains and accelerations in the calcaneus and tibia in situ and in vivo in 1-G. Cadaver experiments were used to relate the global strains and accelerations in the calcaneus and tibia to each other and to external loads and rates of loading. Subsequent human in vivo trials related tibial accelerations and global strains in the calcaneus to external loads elicited by jumping exercises.
- To determine the external loads, rates of loading, global strains in thecalcaneus, tibial accelerations, and the amount of eccentric and concentric whole-muscle activity during jumping exercises in true and in simulated zero-gravity. Each of these aims will be addressed by well-defined, interrelated experiments.. How such loads can be achieved in zero-gravity was investigated with a simulator that negates the effect of gravity on a subject's limbs. The experiments in the simulator were validated with KC-135 aircraft experiments in which true zero-gravity was achieved.
B. Long-Term Goals
- Demonstrate that jumping exercises may be more effective and efficient thancurrent exercises performed in zero-gravity with respect to maintaining bone density and muscle strength.
- Validate the zero-gravity simulator as an appropriate substitute for truezero-gravity experiments during development of an optimum exercise regime.
- Quantify relationships between external loading profiles and internal bonestrains.
C. Importance / Relevance of Work
This knowledge gained from this experiment will not only benefit planners of an in-flight exercise program, but it is also expected that the novel experimental techniques will provide valuable information in the development of exercise-based countermeasures for osteoporosis and muscle atrophy. Moreover, if the zero-gravity simulator is shown to be an appropriate substitute for true zero-gravity experiments, it will provide a much less expensive way to conduct some experiments.
D. Results to Date
In general, we have determined (I) tibial strain data collected from cadaveric limbs arecomparable to values reported in the literature (there are no available comparative values for the strains observed in the calcaneus); (II) statistically significant relationships exist between external forces and internal bone strains and strain rates; (III) peak loads are comparable to loads produced by jumping exercises in vivo; and (IV) data obtained from simulated and true zero-G are comparable.
Cadaver data were collected on fourteen single-leg specimens over a range of peak loads of 300 to 2500N, corresponding to 1 to 5 times body weight. Peak tibial strain ranged up to 0.1% and peak calcaneal strains ranged up to 0.3%. Because of the range of peak loads and tibial strains measured, we have confidence that our test protocol was reasonable and loaded the specimens over a range with an upper limit close to the maximum load that would be encountered in normal circumstances in 1-G.
Twelve subjects were tested in the zero-gravity simulator. Peak external forces during jumping ranged from 1400 to 3100 N, corresponding to 1.7 to 4 times body weight. All of the subjects could elicit loads under the calcaneus which is important given the fact that there is an absence of heel loading in many exercises currently used during extended orbital missions.
Once it was determined that jumping exercises could produce loads large enough to produce strains that have previously been reported to have an osteogenic effect, it was necessary to collect jumping data on a KC-135 microgravity aircraft to validate the ZGS data. Data from the KC-135 show that ground reaction forces were remarkably similar to the ZGS data across all three types of landings, with ground reaction forces differing by no more than 100N. Additionally, loading rates were found to be similar with an average difference of 30kN/s.
In summary, these results support the notion that a suspension-type zero gravity simulator can be used to study certain exercise countermeasures for long-duration missions. When performing the jumping exercises on the KC-135, however, the subjects were jumping on a force plate that was mounted directly to the aircraft. The accelerations imparted by the jump exercise ranged from 0.406g to 0.81g. For jumping to be considered as a countermeasure to bone loss, methods need to be developed to keep accelerations at frequencies below NASA specifications for allowable induced vibrations.
The next step in this research program involves utilizing the information, experience, and expertise gained thus far to design a countermeasure device which permits astronauts to perform tethered jumping exercises without transmitting vibrations to the International Space Station superstructure.
F. Publications From This Research
S.E. D'Andrea, B.L. Davis, D. Lord, A.C. Courtney, G.P. Perusek: External impact leads onthe lower extremity during jumping in simulated microgravity and the relationship to internal bone strain. Submitted to Acta Astronautica, 1997.
G.P. Perusek, B.L. Davis, A.C. Courtney, S.E. D Andrea: An extensometer for global measurement of bone strain suitable for use in vivo in humans. Submitted to Journal of Biomechanics.
G. Abstracts From This Research
Cavanagh, P.R., Davis, B.L., Grabiner, M.D., and Gross, T.S. ''Effects of microgravityon the musculoskeletal system.'' Med. Sci. Sports Exercise, Vol 29, 5, Abstract #1367, S241 1997).
Courtney, A.C., Perusek, G.P., Davis, B.L., Sferra, J., and Kambic, H.E. ''External impact loading and tibial strains in cadaveric lower limbs.'' XVI meeting of the International Society of Biomechanics, Tokyo, Japan (1997).
D'Andrea, S., Davis, B.L., Courtney, A.C., and Perusek, G.P. ''External impact loads on the lower extremity during jumping in simulated microgravity and the relationship to internal bone strain.'' The 12th Man in Space Symposium: The Future of Humans in Space, Washington, DC (June 8 - 13, 1997).
D'Andrea, S., Lord, D., and Davis, B.L. ''A rheological model of the human heel pad.'' The American Society of Biomechanics meeting, Clemson, SC (September 24 - 27, 1997).
Davis, B.L., D'Andrea, S., Lord, D., Courtney, A.C., and Perusek, G.P. ''Lower limb response to impact loads in 1G and micro-G.'' Symposium on the Effects of Microgravity on the Musculoskeletal System, Session G-5 at the 44th Annual Meeting of the American College of Sports Medicine, Denver, CO (May 28 - 31, 1997).
B.L. Davis, S.E. D'Andrea, T. Orlando: Gastrocnemius and Vastus Lateralis actions during jumping in 1G and simulated microgravity. 12th International Congress of ISEK, Montreal, Canada, June 27-30th, 1998.
D Andrea, S. Lower limb response to impact in simulated microgravity and 1G. (Dissertation) The Ohio State University (1998).
D Andrea, S., Davis, B., and Lord, D. ''Rheological modeling of the response of calcaneal bone to high impact loads.'' (oral presentation) NACOB, Waterloo, Ontario, Canada (August 14 - 18, 1998).
B.L. Davis, S.E. D'Andrea, G. Perusek, T. Orlando: Quantifying biomechanical characteristics of jumping exercises in 1G and in simulated and true microgravity. First Biennial Space Biomedical Investigators workshop, League City, Texas, Jan 11-13, 1999.
S.E. D'Andrea, B.L. Davis, G. Perusek, A. C. Courtney: In vivo calcaneal strain during jumping exercises, 45th Annual Meeting of the Orthopaedic Research Society, Anaheim, Feb 1-4, 1999.
S.E. D Andrea, B.L. Davis and G.P. Perusek: Ground reaction forces during countermovement jumps in simulated and true microgravity. 46th Annual Meeting of the American College of Sports Medicine, Seattle WA, 1999.
I. Funding Sources
- National Aeronautics and Space Administration, Office of Life and Microgravity Sciences and Applications (OLMSA)
- UPN/Project Identification: 199-26-17-18
- Solicitation: 95-OLMSA-01
- Initial Funding Date: 1996
- Expiration: 1999