ABSTRACT
INTRODUCTION: Astronauts exhibit sensorimotor changes upon return from long-duration spaceflight that can result in altered gait kinematics and possibly an increased risk of tripping. Toe trajectory during locomotion is a precise motor control task involving both legs, thus providing a composite metric of locomotor control. The purpose of this study was to determine whether astronauts are at an increased risk of tripping after their return from long-duration spaceflight. This was accomplished by assessing the pre- to postflight changes in toe clearance during treadmill walking. METHODS: Ten crewmembers walked on a treadmill while performing a visual-acuity task pre- and postflight. RESULTS: In the three subjects on whom landing day data were available, each exhibited a characteristic of increased tripping risk on landing day: either a decreased median toe clearance or an increased interquartile range (a measure of variance). For all crewmembers, toe clearance median and interquartile range were not significantly different from preflight for the other postflight sessions (the earliest being 1 d after landing). A follow-up analysis showed that changes in foot pitch, ankle dorsiflexion, and pelvis roll angles were significant predictors of changes in toe clearance. DISCUSSION: The landing-day observations indicated an increased risk of tripping, which may pose a hazard during locomotion immediately upon return to Earth, especially in an emergency scenario. However, tripping risk on subsequent days was not different than preflight. The joint angle analysis suggested that the crewmembers tried to reestablish their normal walking pattern postflight, instead of developing a new motor control strategy.
