Hypergravity Resistance Training: Countermeasure to Microgravity
Vincent J. Caiozzo, Ph.D.
University of California, Irvine
A NASA Biomedical Research and Countermeasures Program priority is to determine the potential usefulness of artificial gravity to combat the problem of muscle atrophy and loss of muscle function that occurs in microgravity. Research by Dr. Vincent Caiozzo will test the Space Cycle, a human-powered centrifuge that can be used to generate various levels of artificial gravity/hypergravity. On this bike-like device, the rider pedals in circles around a pole. The project will test whether artificial gravity can be used as a unique resistance training method that acts as an effective solution for preventing the loss of muscle mass and function that occurs due to microgravity.
NASA Taskbook Entry
A program priority of NASAs Human Research Program is to determine the potential usefulness of artificial gravity as a countermeasure, especially with respect to skeletal muscle atrophy and loss of muscle function. This project 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 or hypergravity. The novelty of hypergravity resistance training is that each element of the body is loaded proportional 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.
This project uses the Space Cycle to address the following general hypothesis: hypergravity can be used as a unique resistance training modality that acts as an effective countermeasure, preventing the loss of muscle mass and function that occurs due to microgravity.
In addressing this issue, a logical sequence of experiments was proposed with the following objectives:
- Determine if squats performed under hypergravity conditions, and without external weights, can produce foot forces similar to those seen when performing squat resistance training (SRT) under normal Earth gravity conditions;
- Determine if squats performed under hypergravity conditions produce muscle adaptations similar to those seen using a SRT program under normal Earth gravity conditions; and
- Determine if the squat hypergravity resistance training program is an effective countermeasure to simulated microgravity.
During the past two years, two studies were performed. The first study represents the initial step in testing the hypothesis that hypergravity can be used as a unique modality for resistance training, maintaining the health and function of skeletal muscle in microgravity.
Primary Objectives of Study
- To determine if subjects could perform squats under hypergravity conditions without developing motion sickness or illusory motion;
- To measure foot forces while performing squats under hypergravity conditions; and
- To determine the power required by the cyclist to produce 1.5, 2.0, 2.5 and 3.0 Gz.
All studies were performed using a unique human-powered short-arm centrifuge, the Space Cycle. One of the centrifuge arms of the Space Cycle had a gondola or cage-like configuration that allowed subjects to perform squats. Subjects (male n = 20; and female n = 16) performed squats under hypergravity conditions (1.5, 2.0, 2.5 and 3.0 Gz). During these tests, foot forces were monitored using the Pedar-X system. Foot forces measured under the hypergravity conditions were normalized to foot forces measured at 1 Gz, and these were referred to as relative foot forces. All of the subjects were able to perform the hypergravity squats without developing motion sickness, and illusory motion was minimized by having the subjects fix their sight on the leading edge of the base plate. All of the male and female subjects were able to perform squats at 1.5, 2.0 and 2.5 Gz. However, two male and two female subjects were not able to perform squats at 3.0 Gz because the loading at this hypergravity condition exceeded their strength. The mean relative foot forces at the highest Gz (i.e., 3.0) were 2.3 and 2.5 times greater than body weight for the male and female subjects, respectively. The work rate required to power the Space Cycle was a linear function of Gz and is well within the aerobic scope of most untrained individuals. In conclusion, the findings of this study demonstrate that hypergravity can be used as an effective modality for loading skeletal muscle and that subjects can perform squat resistance exercise without becoming motion sick or experiencing illusory motion.
These data were published in Aviation, Space and Environmental Medicine in 2007.
Objectives of Second Study
- Determine if hypergravity squats can produce foot forces similar to those measured while performing 10-repetition maximum (10-RM) squats under normal 1 Gz condition; and
- Compare the integrated electromyography (iEMG) and goniometry of selected muscles and joints, respectively between hypergravity and 10-RM squats of similar foot forces.
Subjects completed (male = 8 subjects; females = 5 subjects) ten, 10-RM squats (97 12 kg) and 10 hypergravity squats (3.2 0.3 Gz; range of 3-3.75 Gz) under similar average total foot force conditions (104 percent 10-RM) in the same visit. Hypergravity squats were performed on a human-powered short-arm centrifuge. Foot forces were monitored using insole force sensors. Hip and knee flexion/extension, plantar/dorsi flexion, and EMG of the erector spinae, bicep femoris, rectus femoris and gastrocnemius were also monitored during the squats. There were no differences in average total foot forces, average duration per repetition, and iEMG and range of motion of the selected muscles and joints, respectively, between hypergravity and 10-RM squats except a 60 percent greater iEMG of the gastrocnemius muscles during hypergravity squats (P < 0.05). These results suggest that hypergravity squats are comparable to squats performed at 1 Gz and may represent an important countermeasure to microgravity. Collectively, we have performed a series of sequential studies that will culminate in two training studies.
There are potentially several unique aspects of the Space Cycle that may have a direct benefit to Earth-based activities. Currently, it is unclear whether hypergravity may represent a unique loading mode that might enhance training and/or rehabilitation. The unique aspect of hypergravity is that each element is weighted in accordance to its specific gravitational field. In essence, this is like hanging a set of bar bells on every atom/molecule in the body. This distribution of load may be quite different than that of placing weights on a given body structure whereby there is a concentrated loading on that particular structure. Additionally, hypergravity may represent a unique modality for spinal cord injured patients. It is well known that many of these individuals have a reduced orthostatic tolerance. Some have suggested that exposing such individuals to hypergravity may help in this regard. Finally, there may be vestibular aspects of Space Cycle activity that might be of benefit to patients who have balance problems. From our work, we are planning to develop a National Institutes of Health grant that will look at the use of hypergravity as a multisystem rehabilitation tool.