Quantification of the relationship between dynamic grip strength and forearm rotation: a preliminary study

Clinically, the measurement of grip strength is a static measure. It is performed in a standardized posture with the arm at the side, elbow flexed to 90 degrees, and the wrist-forearm positioned in neutral. Many functional activities require dynamic grip strength when an individual moves the wrist-forearm while simultaneously gripping an object. This preliminary study investigated dynamic forearm rotation with isometric grip strength over real time. Thirty wrists from 15 normal subjects were measured with a tilt sensor attached to a strain gauge dynamometer. Each subject underwent randomized trials of maximally gripping the dynamometer while rotating the forearm over a 10-second period. A multiple-regression model was fit for the parameters of extremity, forearm rotation order, fatigue, and loss of strength with supination and pronation. For each parameter, the mean and standard error of its estimate were computed and compared with zero. The significant effects (p = 0.05) of interest were for fatigue and the loss of grip strength from 70 degrees of supination to the end range of supination. Comparisons to existing static grip strength literature were made. We concluded that there is a decrease in grip strength over time as a result of fatigue, there is a decrease in grip strength at supination angles greater than 70 degrees. There is no decrease in grip strength resulting from supination angles less than 70 degrees, nor is there a decrease in grip strength with pronation when measured dynamically. It is suggested that there may be a difference in static and dynamic GS measurements related to forearm rotation.