ANALYSIS OF MUSCLE FATIGUE AND ENERGY EXPENDITURE IN REPETITIVE LIFTING TASKS USING SHAPE MEMORY ALLOY EXOSUIT

This study investigates the effectiveness of a wearable exosuit using shape memory alloys (SMAs) in reducing muscle fatigue and energy expenditure during repetitive lifting tasks. Designed to support the lumbar region without relying on motors or batteries, the SMA-based exosuit offers a lightweight and flexible solution suitable for industrial environments requiring mobility and comfort. Five healthy adult males participated in controlled experiments comparing physiological responses between conditions with and without the exosuit. Each participant performed a 10-min repetitive lifting task involving a 13kg load, and various indicators of physical exertion were measured to evaluate the performance of the exosuit. Key physiological metrics included blood lactate concentration, energy expenditure, respiratory exchange ratio (RER), and muscle fatigue. The results showed that the post-task blood lactate concentration increased significantly in the nonexosuit condition (mean 10.5mmol/L), while the increase was notably smaller (mean 5.5mmol/L) when the exosuit was worn, indicating reduced anaerobic metabolism and muscle fatigue. Similarly, energy expenditure decreased by approximately 16.4% with the exosuit, and improvements were observed in RER values, suggesting a more balanced use of carbohydrate and fat as energy sources. This indicates that the exosuit enhances metabolic efficiency during physically demanding tasks. Muscle fatigue was assessed through median frequency (MF) analysis of surface electromyography (sEMG) signals from key trunk muscles (thoracic and lumbar erector spinae, multifidus). In the exosuit condition, the decline in MF over time was less severe, and final MF values were consistently higher compared to the nonexosuit condition, confirming the exosuit's role in reducing muscular strain during prolonged lifting. These findings demonstrate that SMA-based exosuits can meaningfully reduce physical fatigue and improve efficiency in repetitive work environments. Their motorless, battery-free design provides advantages in terms of weight and wearability, making them well-suited for industrial applications. While the study was limited by a small and homogeneous sample, effect size calculations supported the practical relevance of the observed benefits. Future research should involve larger and more diverse populations and evaluate long-term usability in real industrial settings. Continued development of SMA technology, including improved thermal response and adaptive control, could further enhance the applicability of exosuits across various occupational and rehabilitative contexts.