Assessing hand grip endurance with repetitive maximal isometric contractions.

The purpose of this study was to identify a method for measuring hand grip endurance in patients with hand injury as well as in healthy subjects. Twenty hand-injured patients and 60 healthy subjects participated in the study. Each subject performed two sets of maximal repetitive isometric contractions on the Grippit instrument for 180 seconds, with a contraction time of 2.5 seconds and a rest time of 1 second. Reliability data were high for initial grip force and for absolute and relative endurance values at 90 seconds (r range, 0.73 to 0.97, p < 0.001). Relative endurance at 180 seconds, though, showed weaker reproducibility (r = 0.54, p < 0.01). A measuring period of 90 seconds instead of 180 seconds is suggested, because of the results of test-retest reliability. The method allows endurance to be described in relative force values (as a percentage) as well as in absolute force values (Newtons).