An Optimal Method of Training the Specific Lower Limb Muscle Group Using an Exoskeletal Robot

This paper suggests a novel method of strengthening specific muscle groups in the lower limb during a functional movement. When the foot of an user wearing an exoskeletal robot follows a given path, the contribution of each muscle group to generate the motion changes along the path of the trajectory. The efficiency of muscle training, which is defined as the ratio of the work of a specific muscle group to that of all groups, can be maximized by changing the training load along the path. Based on a musculoskeletal model, the contribution of each muscle group along the path can be calculated as a function of its position. When a specific muscle group is chosen for exercise or rehabilitation, the efficiency of training can be maximized by setting high load where its contribution is high and low load where its contribution is low. By doing so, the user can exercise longer with the same amount of energy consumption. The EXOWheel that features a lower limb exoskeleton is employed to verify the method and the hamstring muscle group is selected as the specific muscle group. Three healthy subjects participate in the experiment, and electromyogram sensors are employed to monitor the muscle power. The results indicate that the efficiency of the hamstring muscle group for a given circular foot path under the optimal training load is 46.2% compared with 32.5% with a constant load and it means the 42% higher efficiency of the specific muscle group training.