Grip Strength in Different Elbow and Forearm Positions

The purpose of this study was to test for differences in the grip strength among the six different combinations of elbow and forearm positions. The dominant hand of sixty normal subjects was tested for maximal grip strength in elbow flexion at 90 degrees with forearm in pronation, midposition, and supination and elbow at full extension with forearm in pronation, midposition, and supination. The six positions were randomized and the grip strength was measured by Jamar Dynamometer. Surface EMG of the biceps brachii of the dominant upper extremity was recorded simultaneously during grip testing. The result of two-way analysis of variance (ANOVA) revealed that elbow or forearm position could significantly change grip strength (p＜0.001). There was also significant interaction between elbow and forearm position (p＜0.05). Further post hoc test with Student-Newman-Keuls multiple comparison showed that grip strength in the position of elbow flexion at 90 degrees with forearm pronation was significantly lower than those in the same elbow position with other forearm position and those in the same forearm position with other elbow position. It appeared to be similar results if we analyzed the male and female data separately. Furthermore, the regression coefficient between grip strength and integrated EMG of biceps brachii in the six positions is only 0.37 at 0.001 significant level. It suggested that the reasons for differences of grip strength in different elbow-forearm positions might mainly be other biomechanical factors.