HYPERGRAVITY RESISTANCE TRAINING IN FEMALES: COUNTERMEASURE TO MICROGRAVITY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Note: If you are applying for exempt or expedited status, please provide a justification for the appropriate category here. 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 (15,16), 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. Given this background, the current proposal is a "proof-of-principle" of a unique countermeasure technology referred to as the "Space Cycle." The Space Cycle is a human powered centrifuge that can be used to generate various levels of artificial gravity (53; see Figure 1, APPENDIX A). To our knowledge, the Space Cycle is the only human powered centrifuge in the United States that is currently operational. The primary objective of this proposal 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. For the purposes of this study, 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 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 (26). 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. Development of the Space Cycle. As described in APPENDIX A, we have developed two versions of the Space Cycle. The newest version of the Space Cycle has a radius of 6 feet and is compatible with the dimensions of the International Space Station. The Space Cycle has an aluminum frame that houses a moving drive system and restraints for riders. The frame can be configured so that the legs and/or upper body musculature are required to produce power. Additionally, the centrifuge arms can be easily removed and modified according to the type of activity desired. The physiological instrumentation of the Space Cycle includes: i) instrumented foot pedals that can be used to measure torque, work, and power; and ii) monitors for blood pressure, heart rate, and oxygen consumption (using a ViaSys VmaxST telemetry unit). Work and power are controlled using a caliper brake system and are monitored by telemetry. For the purposes of the current grant proposal, the passive centrifuge arm will be modified such that subjects can perform squats under hypergravity conditions.