Optimum joint angles in dynamic gripping

Date of Completion

January 2006


Health Sciences, Recreation




The determination of optimum joint angles of the hand could have implications in ergonomics, tool design, and hand rehabilitation. Strong evidence in the literature shows that forceful hand and wrist exertions increase risk for wrist tendonitis and carpal tunnel syndrome. Efforts to optimize musculoskeletal function during tasks could significantly reduce the risk of injury. Optimal joint position is the joint angle at which optimal muscle length and moment arms occur together. The optimal joint angle of the proximal interphalangeal (PIP) and metacarpal phalangeal (MCP) joints of the index finger at differing wrist positions were determined by simultaneous electromyography and potentiometry of joint position during dynamic gripping under a constant load. Ten male and ten female aged matched subjects participated in the present study. Subjects were asked to flex the proximal interphalangeal joint under a constant load of one pound with the metacarpal phalangeal joint in extension at various wrist positions. The wrist positions were zero degrees, 15 degrees flexion, 15 degrees extension, 30 degrees flexion, and 30 degrees extension. The same procedure was conducted for the metacarpal phalangeal joint with the proximal interphalangeal joint in extension. The influence of forearm and hand anthropometrics was also study. The results were also compared to predictive values as determined by excursion and moment arms calculations. No significant differences were found between genders for optimal joint positions except at the MCP joint with the wrist at 0 and 30 degrees flexion. No significant differences were found within subjects as a function of wrist position. No significant effect was seen for hand and forearm anthropometrics. No significant differences were found between actual predicted values of optimal joint angles with the wrist in neutral. ^ The results appear to show that optimum joint angles are a function of tendon excursion and moment arm characteristics that are not influenced by gender, wrist position or forearm and hand anthropometrics. ^