Effects of an active exoskeleton on the muscle activity of the erector spinae and biceps femoris muscles during lifting with symmetric stoop and squat technique

Introduction Active exoskeletons are increasingly used to reduce muscle activity and support lifting tasks. However, the effectiveness of exoskeletons can vary depending on the lifting technique. This study investigates the effects of a commercially available active exoskeleton (Apogee) on muscle activity during two different lifting techniques: stoop and squat. Methods 17 healthy young adults (8 male, 9 female) participated in the study. Muscle activity was measured in the M. erector spinae (MES) and M. biceps femoris (MBF) using EMG while lifting a 15 kg box in four conditions: 1) without exoskeleton, 2) exoskeleton in passive mode, 3) 50% support and 20% counterforce, 4) 100% support and 60% counterforce. Results The MBF activity was 29% lower during the squat technique compared to the stoop technique (F 1 , 16 = 20.53, p 0.01, ղ P 2 = 0.56). MES activity was similar across both techniques (F 1,15 = 0.53, p = 0.48, ղ P 2 = 0.03). When pooling data across techniques, the exoskeleton significantly reduced MES (F 1,45 = 18, p 0.01, ղ P 2 = 0.53) and MBF activity (F 1,48 = 10.2, p 0.01, ղ P 2 = 0.39), with higher support levels leading to greater reductions in muscle activity. The stoop technique benefitted more from the exoskeleton, showing significant reductions in MES activity (10%–27% MVC) and MBF activity (7%–10% MVC). In contrast, squat lifting showed a significant reduction in MES (10%–17% MVC) activity but no significant reduction in MBF (2%–3% MVC) activity. Discussion The results indicate that the exoskeleton provides greater benefits during the stoop technique, where the lifting motion primarily involves hip extension. The reduction in muscle activity supports the potential of exoskeletons in reducing muscle load and preventing work-related musculoskeletal disorders (MSDs). However, the squat technique showed limited improvements, suggesting that exoskeletons may need to be adapted for different lifting tasks. Future exoskeletons should aim to dynamically adjust their support based on the specific lifting technique to maximize effectiveness.