This paper proposes a close-fitting assistive suit, called e.z.UP®, with a passive actuation mechanism composed of an adjustable structure. The suit can adequately assist the back and arm muscles of a user with the proposed layout of an arm assistive belt and a two-layer structure, respectively. With its lightweight characteristic (i.e., weighing 0.75 kg only), the proposed suit is portable and easy to wear without additional burden. By using the averaged Japanese body data, a simulation was conducted based on a human body model wearing our proposed suit to evaluate the layout of the arm assistive belt. The simulation results prove that the proposed suit can adequately assist the user’s arm muscles based on the user’s motion. An experiment involving the measurement of muscle activities is also implemented with seven young subjects and seven middle-aged subjects to evaluate the arm assistive belt and the two-layer structure. The experimental results reveal that the proposed suit can successfully and appropriately assist both the arm and back muscles simultaneously.

This paper proposes a three-layer elastic cloth fabric mechanism for an assistive suit with adjustable structure (based on a two-layer non-adjustable structure) to achieve different assistive force profiles. This increases the assistive force on the lower-back muscle group and alleviates the undesired pre-tension that acts on a user when the rubber belt located on the back is pulled to provide a higher assistive force. With the lower pre-tension, users would not encounter body fatigue as rapidly as in the past. The adjustable feature enables the structure to provide a force that increases gradually to a high level over a short distance without pre-tension. An experiment involving the measurement of muscle activities is conducted to evaluate the variation in assistive force in the lower back by comparing the three-layer suit to the two-layer non-adjustable suit. The experimental results show that the new three-layer structure successfully assists without pre-tension in the lower-back muscle group similar to the two-layer structure with pre-tension. A simple questionnaire is also administered to collect feedback from participants on the differences between the three-layer suit and two-layer suit in terms of wearing perception. Over half of the participants reported that the perception of pre-tension in the three-layer suit is lower than that in the two-layer suit.

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