Lower Extremity Exoskeleton Reduces Back Forces in Lifting

We propose a lower extremity exoskeleton device which adds a passive extensor moment (restoring moment) about the hips during squat lifting, thus reducing forces on the lower back by reducing the required extensor muscle force. Video sequences were recorded of normal speed sagittal squat lifting 44.5 N (10 lb) and 133.5 N (30 lb) packages for marker tracking. Calculations suggested that the device reduces maximum spine compressive forces by approximately 1300 N. Surface electromyography (EMG) was performed on 6 subjects supporting 44.5 N (10 lb) and 133.5 N (30 lb) packages in the static squat posture. With the device, back muscles demonstrated a 54% reduction in muscle activity. This exoskeleton device includes features not available on other devices including highly adjustable moment profile and elimination of high contact stress in the lower extremities by connecting directly with the ground.