Influence of exercise-induced local muscle fatigue on the thumb and index finger forces during precision pinch

The thumb and index finger are important digits to performed dexterous and complex manipulation of objects. However, the local muscle fatigue will induce the capacity of force production and impair the precision motor control of the thumb and index finger. This study focused on the exercise-induced local muscle fatigue influencing the COP (center of pressure) area, the SD and the PA (projection angle) of both the thumb and index finger and the CA (coordination angle) of two force vectors. Sixteen right-handed female subjects participated in this study. They performed the experiments including MVC, precision pinch and fatigue generation. The results show that the local muscle fatigue led an obvious increase in the COP area regardless of hands and digits, but only a great numerical increase in the SD of grip force in both digits of the left hand. Furthermore, for the CA of two force vectors, the statistical analysis showed a greater value in post-fatigue than that in prefatigue, there was no difference between both hands. No consistent significant difference of the PA was observed in both digits of both hands. However, the PA of the thumb force vector was bigger than that of index finger. The findings shed light on the exercise-induced local muscle fatigue had a significant effect on the force vector and the stability of force amplitude and provided a understanding of the force vectors, even could applied in a manual labor fatigue detection, and we also got that the local muscle fatigue has an obvious periphery mechanism.