Muscle activation during body weight-supported locomotion while using the ZeroG

The ZeroG provides dynamic body weight support (BWS) using a harness while individuals with mobility impairments (e.g., spinal cord injury) ambulate overground. Muscle activity during locomotion using this device was studied in 13 nondisabled adults (age 23.8 +/- 2.7 yr). Electromyography (EMG) recordings were collected from tibialis anterior (TA), medial gastrocnemius (MG), rectus femoris (RF), and biceps femoris muscles during randomized walking trials at preferred speeds under five levels of BWS (0%, 20%, 40%, 60%, 80%). Filtered EMG signals from each trial were normalized to 0% BWS and correlated with gait phases. Muscle activity, averaged across muscles, decreased significantly at heel strike by 33.4% with increasing BWS. Offloading significantly decreased heel strike activity of RF (62.8%), MG (35.5%), and TA (25.9%). Gait cycle completion time increased with BWS primarily because of increased swing phase time. These results summarizing the effect of BWS on muscle activation during ambulation can now be compared with clinical populations using the ZeroG.