Abstract
The aim of this study was to evaluate the muscle activities and subjective discomfort according to the heights of tasks and the lower-limb exoskeleton CEX (Chairless EXoskeleton), which is a chair-type passive exoskeleton. Twenty healthy subjects (thirteen males and seven females) participated in this experiment. The independent variables were wearing of the exoskeleton (w/ CEX, w/o CEX), working height (6 levels: 40, 60, 80, 100, 120, and 140 cm), and muscle type (8 levels: upper trapezius (UT), erector spinae (ES), middle deltoid (MD), triceps brachii (TB), biceps brachii (BB), biceps femoris (BF), rectus femoris (RF), and tibialis anterior (TA)). The dependent variables were EMG activity (% MVC) and subjective discomfort rating. When wearing the CEX, the UT, ES, RF, and TA showed lower muscle activities at low working heights (40–80 cm) than not wearing the CEX, whereas those muscles showed higher muscle activities at high working heights (100–140 cm). Use of the CEX had a positive effect on subjective discomfort rating at lower working heights. Generally, lower discomfort was reported at working heights below 100 cm when using the CEX. At working heights of 100–140 cm, the muscle activity when wearing the CEX tended to be greater than when not wearing it. Thus, considering the results of this study, the use of the lower-limb exoskeleton (CEX) at a working height of 40–100 cm might reduce the muscle activity and discomfort of whole body and decrease the risk of related disorders.
Highlights
The results showed that the activities of the erector spinae (ES) and GAS muscles were significantly lower during high siting and low sitting EXO tasks, respectively, than during standing
Without wearing the CEX (w/o), muscle activity differed according to working height
This study analyzed the muscle activity and subjective discomfort associated with use of the CEX based on working height
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Work-related musculoskeletal disorders (WMSDs) of both the upper and lower extremities have become a major concern in many industries, such as the manufacturing, agricultural, forestry, and fishery sectors. WMSDs cause muscles, tendons, and nerves to be stressed and loaded due to excessive or repetitive exertive force, awkward body posture, less resting time, cold working environment, vibration, and so on. According to the Bureau of Labor Statistics [1], shoulder, back, and knee injuries comprise 15.2, 8.8, and 39.0%, respectively, of all WMSDs. There is evidence that a manual material handling (MMH) with the arms above the head, lifting weights, prolonged kneeling, and squatting can increase the risk of shoulder, back, and knee-related disorders [2,3]
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