Effects of body weight unloading on electromyographic activity during overground walking

Background: Body weight unloading (BWU) on treadmills is a common method of gait rehabilitation. However, treadmills slightly but significantly modify gait biomechanical parameters thus confound the effects of BWU. By conducting our experiments under conditions that replicate daily walking and controlling for speed variability, with a mechanical device designed to pull the BWU system at a constant speed, this study could assess the unique effects of BWU on gait electromyography (EMG) of healthy subjects. Methods: Fifteen healthy subjects walked overground in a control (no suspension vest) and three (0%, 15%, 30%) BWU experimental conditions. The EMG activity of the Tibialis Anterior (TA), Lateral Gastrocnemius (LG), Vastus Lateralis (VL), and Rectus Femoris (RF) were recorded (six trials per condition). Results: ANOVA showed significant differences in the peak activity and integrated EMG of the TA, LG and VL. Pairwise comparisons of EMG parameters under 0% vs. 15% and 15% vs. 30% BWU levels showed that the increase in BWU levels decreased the peak and integrated EMG of the TA, LG, and VL without pattern modification. Conclusion: Overground gait with up to 30% BWU reduces joint loads without modifying the muscle activation patterns. Several clinical applications for overground gait reeducation with BWU are suggested.