Relative optimum grip span as a function of hand anthropometry

This study investigates the optimum grip span relative to an individual's hand anthropometry (ROGS) for an isometric power grip exertion. Maximum voluntary isometric grip force (MVGF), muscular activity (EMG) and subjective rating (SR) were used as criteria. Two complementary experiments were conducted. In both experiments, nine different widths of span, separated with 0.5cm intervals, were tested across 12 subjects. The span size was a function of one's modified thumb crotch length (TCLm). In the first experiment, the grip spans were tested as a function of MVGF and SR. The results of this experiment indicate TCLm-2 as the ROGS. The SR was also supportive of this result. In the second experiment, EMG at a constant force (30% MVGF) was evaluated as a function of the grip span. The EMG based efficiency coefficients indicate TCLm-2.5 as the optimum span, resulting in the least muscular activity. Based on the analysis of MVGF, EMG and SR, the ROGS is in the interval, TCLm-2.5 less than or equal to ROGS less than or equal to TCLm-2, indicating a precise location of optimum grip span as a function of one's TCLm. This result suggests that hand-powered tools with two-handles should be designed for adjustability as a function of TCLm.