The relationship between wrist position, grasp size, and grip strength.

In the first part of this study, the position assumed by a normal wrist during unconstrained maximal grip and the relationship between wrist position and grip strength were investigated in 20 healthy subjects. Grip strength and wrist position were recorded in the self-selected position and then again while the subjects voluntarily deviated the wrist randomly into flexion, extension, or radial or ulnar deviation of 10 to 15 degrees. The self-selected position was 35 degrees of extension and 7 degrees of ulnar deviation. Grip strength was significantly less in any position of deviation from this self-selected position, even after accounting for fatigue. With the wrist in only 15 degrees of extension or in neutral radio-ulnar deviation, grip strength was reduced to two thirds to three fourths of normal. Sex did not affect wrist position. The dominant wrists were within 5 degrees of the nondominant ones but were relatively less extended and in more ulnar deviation. Grip strength is significantly reduced when wrist position deviates from this self-selected optimum position. In the second part of the study, the effect of grasp size on this self-selected position was studied in 21 subjects. The degree of wrist extension was inversely and linearly related to how large a setting on the Jamar dynamometer was used. This was true regardless of hand size, although the effect was more significant for smaller hands. Radial and ulnar deviations were not affected by handle position. A minimum of 25 degrees of wrist extension was required for optimum grip strength.(ABSTRACT TRUNCATED AT 250 WORDS)