The aim of this study was to propose a tread swing mechanism for lower-limb strength training devices and to confirm its effects. In the standing position and for training the lower limbs, if the tread-surface angle is inappropriate, the posture of the knee joints gets affected, and knee adduction/valgus moments, which result in knee stress, get generated. The target training exercises are the front-back leg scissors and open-close leg triangle exercises. With regard to the swing of the tread, it is necessary to realize a pitch/yaw rotation and a roll/yaw rotation for the former and the latter exercises, respectively. As a result, knee joint stress can be reduced by moving the center of pressure (COP). The proposed mechanism has a further differential mechanism that utilizes the difference between the pulley diameters. The translational movement force of the tread is transmitted as the torque of the swing motion for the pitch, roll, and yaw through the effects of a differential mechanism. The rate of the swing angle can be changed by adjusting the pulley diameter. As a result of evaluating the effect of exercises using a manufactured device, it was confirmed that the tread performed a predetermined swing motion. It was also confirmed that the COP position changed. Therefore, it is expected that knee joint stress will reduce. Rehabilitation and strength training that result in small knee joint stresses and generate large muscle load are in great demand for people experiencing knee joint failure.

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