Locomotion in simulated and real microgravity: horizontal suspension vs. parabolic flight.

INTRODUCTION The effect of reducing gravity on locomotion has been studied using microgravity analogues. However, there is no known literature comparing locomotion in actual microgravity (AM) to locomotion in simulated microgravity (SM). METHODS Five subjects were tested while walking at 1.34 m x s(-1) and running at 3.13 m x s(-1) on a treadmill during parabolic flight and on a microgravity simulator. The external load (EL) in AM and SM was provided by elastomer bungees at approximately 55% (low) and 90% (high) of the subjects' bodyweight (BW). Lower body joint kinematics and ground reaction forces were measured during each condition. Effect size and its 95% confidence interval were computed between gravitational conditions for each outcome variable. RESULTS In AM, subjects attained approximately 15-21 degrees greater hip flexion during walking and 19-25 degrees greater hip flexion during running. Hip range of motion was greater in AM during running by approximately 12-17 degrees. Trunk motion was 4 degrees less in SM than AM during walking. Peak impact force was greater in SM than in AM during walking with a low EL (SM = 0.95 +/- 0.04 BW; AM = 0.76 +/- 0.04 BW) and contact times were greater in SM. CONCLUSIONS Subtle differences exist in locomotion patterns, temporal kinematics, and peak impact ground reaction forces between AM and SM. The differences suggest possible adaptations in the motor coordination required between gravitational condition, and potential differences in adaptations that are dependent upon if training occurs in actual or simulated microgravity.