NEUROMUSCULAR ACTIVATION PATTERNS DURING TREADMILL WALKING AFTER SPACE-FLIGHT

Astronauts adopt a variety of neuromuscular control strategies during space flight that are appropriate for locomoting in that unique enviro nment, but are less than optimal upon return to Earth. We report here the first systematic investigation of potential adaptations in neuromu scular activity patterns associated with post flight locomotion. Astro naut-subjects were tasked with walking on a treadmill at 6.4 km/h whil e fixating a visual target 30 cm away from their eyes after space flig hts of 8-15 days. Surface electromyography was collected from selected lower limb muscles and normalized with regard to mean amplitude and t emporal relation to heel strike. In general, high correlations (more t han 0.80) were found between preflight and postflight activation wavef orms for each muscle and each subject; however, relative activation am plitude around heel strike and toe off was changed as a result of flig ht. The level of muscle cocontraction and activation variability, and the relation ship between the phasic characteristics of the ankle musc ulature in preparation for toe off also were altered by space flight. Subjects also reported oscillopsia during treadmill walking after flig ht. These findings indicate that, after space flight, the sensory-moto r system can generate neuromuscular-activation strategies that permit treadmill walking, but subtle changes in lower-limb neuromuscular acti vation are present that may contribute to increased lower limb kinemat ic variability and oscillopsia also present during postflight walking.