Effect of long-duration spaceflight on postural control during self-generated perturbations

This report is the first systematic evaluation of the effects of prolonged weightlessness on the bipedal postural control processes during self-genera ted perturbations produced by voluntary upper limb movements. Spaceflight i mpacts humans in a variety of ways, one of which is compromised postflight postural control. We examined the neuromuscular activation characteristics and center of pressure (COP) motion associated with arm movement of eight s ubjects who experienced long-duration spaceflight (3-6 mo) aboard the Mir s pace station. Surface electromyography, arm acceleration, and COP motion we re collected while astronauts performed rapid unilateral shoulder flexions before and after spaceflight. Subjects generally displayed compromised post ural control after flight, as evidenced by modified COP peak-to-peak anteri or-posterior and mediolateral excursion, and pathlength relative to preflig ht values. These changes were associated with disrupted neuromuscular activ ation characteristics, particularly after the completion of arm acceleratio n (i.e., when subjects were attempting to maintain upright posture in respo nse to self-generated perturbations). These findings suggest that, although the subjects were able to assemble coordination modes that enabled them to generate rapid arm movements, the subtle control necessary to maintain bip edal equilibrium evident in their preflight performance is compromised afte r long-duration spaceflight.