Introduction: This study represents the first step toward testing the hypothesis that hypergravity can be used as a unique resistance training modality for maintaining the health and function of skeletal muscle in microgravity. The primary objectives of this study were to use a human-powered short-arm centrifuge for the following: 1) to determine whether subjects could perform squats under hypergravity conditions without developing motion sickness or illusory motion; 2) to measure foot forces while performing squats under hypergravity conditions; and 3) to determine the mechanical power required to produce 1.5, 2.0, 2.5, and 3.0 Gz (head to foot) at the feet.
Methods: Subjects (22 males and 19 females) performed 10 squats each at 1.5, 2.0, 2.5, and 3.0 Gz on a human-powered short-arm centrifuge, the space cycle. Foot forces during each squat were monitored using insole force sensors, and normalized to foot forces measured at 1 Gz (relative foot forces).
Results: Illusory motion was minimized using a visual focal point, and did not affect the ability of subjects to perform squats. The mean standing relative foot forces at 3.0 Gz were 2.3 and 2.4 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 untrained individuals.
Discussion: 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 developing motion sickness or illusory motion.