Hypergravity Resistance Training Project
A. Profound Deconditioning Occurs in Microgravity
The effects of spaceflight on various physiological systems are clearly profound, and despite extensive research are incompletely understood. It is widely recognized, within both the space and scientific communities, that even short periods of exposure to microgravity can produce vestibular dysfunction, losses in muscle strength and function, and loss of orthostatic tolerance. Hence, there is a substantial amount of concern regarding the physiological deconditioning that might occur during longer duration spaceflights, for instance to Mars. Within this context, several countermeasures have been developed, but none appear to be completely effective. Therefore, a program priority of NASA’s Biomedical Research and Countermeasures Program (NRA-03-OBPR-04) is to determine the potential usefulness of artificial gravity as a countermeasure, especially with respect to skeletal muscle atrophy and loss of muscle function. As Burton noted (ref), the most obvious countermeasure to microgravity is a centrifuge, yet it has been the least explored. There are some obvious applications of artificial gravity as a countermeasure to microgravity. For instance, artificial gravity could be used to impose orthostatic challenges on the cardiovascular system, possibly preventing the loss of orthostatic tolerance that occurs as a result of microgravity. There are also some potential applications of artificial gravity in a microgravity environment that are not as obvious. As an example, artificial gravity/hypergravity in a microgravity environment could be used as a novel method of performing resistance training under high loading conditions. The novelty of artificial gravity/hypergravity resistance training is that each element of the body is loaded proportionally to the local gravitational field, and under hypergravity conditions muscles like those of the leg can be made to work against very high loads (e.g., + 2 body weights) without the need for external weights. For instance, performing squats (a target exercise performed by astronauts on the International Space Station) under a hypergravity load of 2 body weights would be approximately equivalent to an individual (body weight of 200 lbs) performing squats using a 200 lb weight in a normal 1 G environment.
B. Objectives
The Space Cycle research program seeks to test a “proof-of-principle” of a unique human powered centrifuge that can be used to generate various levels of artificial gravity. The primary objective of our project is to use the Space Cycle to address the following general hypothesis: Artificial gravity can be used as a unique resistance training modality that acts as an effective countermeasure to microgravity, preventing the loss of muscle mass and function. In addressing this issue, a logical sequence of experiments is proposed with the following objectives: i) determine if squats under hypergravity conditions and without external weights can produce foot forces similar to those seen when performing squat resistance training (SRT) under normal 1 G conditions; ii) determine if squats performed under hypergravity conditions produce muscle adaptations similar to those seen using a squat resistance training program under normal 1 G conditions; iii) determine if squat hypergravity resistance training (SHRT) program is an effective countermeasure to simulated microgravity. We are focusing on SRT because squats recruit a broad spectrum of muscles in the leg and back, and are one of the classical exercises used by bodybuilders and athletes to hypertrophy muscles of the leg. Additionally, the so-called antigravity muscles of the leg are at the greatest risk for atrophy induced by microgravity. Furthermore, as noted above, squats are a target exercise performed by astronauts on the International Space Station. In achieving the objectives noted above, it will be possible to test the following hypotheses.
C. Hypotheses
1. Foot force hypothesis:
Previous studies show that hypertrophy of skeletal muscles occurs when they contract under high loading conditions. Perhaps the best illustration of this is the development and popularization of the repetition maximum (RM) concept that was initially pioneered by DeLorme (ref). Using the Space Cycle, we hypothesize that it can be used to create hypergravity-loading conditions that result in foot forces similar to those seen when performing a 10 RM set of squats in a normal 1 G environment.
2. Hypergravity resistance training (HRT) hypothesis:
By definition, SHRT is used refers to resistance training that employs hypergravity as the loading modality rather than external weights. This hypothesis states that SHRT on the Space Cycle under conditions that produce foot forces similar to those seen when performing SRT in 1 G will result in muscle hypertrophy (just as is seen under normal 1 G conditions).
3. Countermeasure hypothesis:
This hypothesis states that SHRT can be used as an effective countermeasure to microgravity, preventing the loss of muscle mass and function normally associated with exposure to microgravity.
1. Burton RR. A human-use centrifuge for space stations: proposed ground-based studies. Aviat Space Environ Med 59: 579-581, 1988.
2. Burton RR and Meeker LJ. Physiologic validation of a short-arm centrifuge for space application. Aviat Space Environ Med 63: 476-481, 1992.
3. DeLorme TL. Progressive resistance exercises. New York: Appleton-Century-Crofts, 1951.