Muscle activity and Ground Reaction Force-based control strategies for actuating soft wearables using Squat motion

The squat posture is the most recommended activity for training the lower body muscles primarily in sports and rehabilitation. However, the current soft exosuit wearable is actuated based on the assist and resist nature of the squat. Limitations of such soft wearables include parameter optimization to enhance the subject's performance. Hence, we proposed an approach to determine the feasible lower limb muscular activity by obtaining surface electromyographic (sEMG) signals. In contrast, the vertical ground reaction forces (vGRF) were obtained from force plates to cross-validate the importance of vGRF and its overlapping nature with the sEMG data. Three healthy volunteers with no abnormalities were included in this study. Each participant was allowed to perform unloaded isometric squat motion in three phases. The phases include proper eccentric (30%), load at peak (60 %) and concentric phases (100%) of the predefined squat sessions. Electromyographic signals (Delsys Inc., Boston, MA, USA) were obtained for seven major muscles in the lower limb using Trigno Wireless sensors and the force plate data were obtained in synchronization using Bertec Solutions. The comparative results confirmed that the Rectus Femoris muscle of the quadriceps group has maximum activity during the descent phase of (116.2)%MVC. At the same time, the Vastus Medialis and Vastus Lateralis muscles from the quadriceps group show a higher activation pattern during load at peak phase, even though the Rectus Femoris begin to have lower activation during the ascent phase. Also, the amplitude characteristics of the Vastus Medialis and Vastus Lateralis and Gluteus Maximus muscle groups show more significance in the vertical ground reaction force (vGRF) pattern. These findings indicate that the vGRF could also be used as an actuating parameter in addition to sEMG to actuate the soft wearable exosuits based on biomechanical applications.