ADAPTATION OF NEUROMUSCULAR ACTIVATION PATTERNS DURING TREADMILL WALKING AFTER LONG-DURATION SPACE-FLIGHT

The precise neuromuscular control needed for optimal locomotion, parti cularly around heel strike and toe off, is known to be compromised aft er short duration (8- to 15-day) space flight. We hypothesized here th at longer exposure to weightlessness would result in maladaptive neuro muscular activation during postflight treadmill walking. We also hypot hesized that space flight would affect the ability of the sensory-moto r control system to generate adaptive neuromuscular activation pattern s in response to changes in visual target distance during postflight t readmill walking. Seven crewmembers, who completed 3- to 6-month missi ons, walked on a motorized treadmill while visually fixating on a targ et placed 30 cm (NEAR) or 2 m (FAR) from the subject's eyes. Electroni c foot switch data and surface electromyography were collected from se lected muscles of the right lower limb. Results indicate that the phas ic features of neuromuscular activation were moderately affected and t he relative amplitude of activity in the tibialis anterior and rectus femoris around toe off changed after space flight. Changes also were e vident after space flight in how these muscles adapted to the shift in visual target distance. (C) 1998 Elsevier Science Ltd. All rights res erved.