Abstract
Background/Objectives: Preoperative muscle atrophy leads to persistent gait abnormalities in patients undergoing total hip arthroplasty (THA). Efficient motor learning of the gluteus medius is crucial for their recovery. In this study, a single-joint hybrid assistive limb (HAL) was developed to assist hip abduction. We aimed to evaluate the muscle activity and safety of this device during hip abduction in healthy adults. Methods: Ten healthy adults (five males and five females; mean age, 40.7 years) with no hip disorders performed one set of 30 repetitions of side-lying hip abduction under three conditions: without HAL (pre-HAL), with HAL, and without HAL (post-HAL). Muscle activities of the gluteus medius, gluteus maximus, tensor fasciae latae, rectus femoris, and biceps femoris (expressed as percentage of maximum voluntary contraction [%MVC]); vital signs; hip visual analog scale (VAS); and hip abduction and flexion angles were assessed. The mean values were compared among the conditions. Results: The %MVC of the gluteus medius significantly increased from 52% (pre-HAL) to 75.4% (HAL) and then decreased slightly to 61.6% (post-HAL). No other muscle groups showed significant changes. Vital signs and hip VAS scores showed no significant variation. Although no significant differences were found in the hip abduction and flexion angles, a reduction in the hip flexion angle was observed in the HAL and post-HAL conditions. Conclusions: The hip abduction HAL effectively and safely enhanced gluteus medius activity. Reduction in the hip flexion angle during HAL and post-HAL suggests the possibility of appropriate abduction movements and motor learning effects.