In which phase of the lifting motion is the assist suit we developed effective?

The purpose of this study is to verify the load-reducing effect on the lower back muscles of the prototype assist suit with artificial muscles, focusing on the effectiveness in each phase of the lifting motion.

In this experiment, we conducted a lifting task under two conditions, with and without wearing the prototype assist suit (KOGANEI Co., Ltd.) (subjects: 17 healthy adult males). The lifting motion started from a standing posture, with the phases defined as follows: Phase 1 was from the standing position to gripping the container, Phase 2 was from lifting the container to standing upright, Phase 3 was from standing to lowering the container, and Phase 4 was from lowering the container to returning to the standing position, with each phase lasting 4 seconds. The target muscles were the longissimus (LG), iliopsoas (IC), and multifidus (MF), and electromyographic sensors were attached according to the SENIAM sensor locations. The recorded EMG signals were processed using ARV, and the average EMG for each phase was calculated. The average EMG of the prototype was divided by the average EMG when the assist suit was not worn, and the percentage was calculated.

When wearing the assist suit, the muscle activity of the three muscles in the erector spinae decreased by 3.0% to 12.7% compared to when the assist suit was not worn. The percentage of muscle activity in each phase was as follows: in Phase 1, the average muscle activity for LG, IC, and MF was 86.0%, 82.7%, and 93.2%, respectively; in Phase 2, 96.1%, 92.8%, and 102.0%; in Phase 3, 91.6%, 91.1%, and 96.6%; and in Phase 4, 92.4%, 90.5%, and 97.5%.

Compared to the condition without wearing the assist suit, the assist suit we developed reduced muscle activity in the lower back, with the most significant effect observed during Phase 1.

The assist suit demonstrated effectiveness in the early phase of the lifting motion, where lower back pain is more likely to occur. Moving forward, we aim to gather feedback from users regarding wearability through validation trials in hospitals and care facilities, and improve the assist suit to contribute to reducing lower back pain.