Assessment of Muscle Fatigue Based on the Reaction Force of Muscles for a Basis of Developing a Massage Robot

Massage therapy is crucial in the field of physical activities and sports to recover muscle fatigue and reduce stress. However, the physical workload on massage therapists is demanding, and the number of therapists is limited. To solve these problems, a massage robot that can move with human-like flexibility and delicacy was develop using a five-fingered robotic hand that mimicking a human hand. Moreover, the aim of this research is to develop a method of online estimation of a user’s fatigue based on the muscle hardness in order to evaluate the effect of massaging from tactile information of the robot hand finger-tips to perform appropriate treatment. In this paper, we constructed a system about to measure muscle hardness based on reaction forces and measuring changes in muscle hardness and subjective fatigue over time before and after exercise. Then, the experiment of measuring muscle fatigue was conducted. As a result, the correlation coefficient between changes in muscle hardness and subjective fatigue highly correlated with five of the seven experimental participants. The result suggests the possibility that changes in the reaction force of muscles can be used as a measure for muscle fatigue recovery.