The measurement of palmar abduction strength of the thumb (PAST) is often used as a research tool to provide an objective assessment of thenar muscle function in patients with carpal tunnel syndrome (CTS). The purpose of this study is to determine the effect of blocking radial abduction on PAST in a normal population. PAST was measured for both hands of 100 healthy volunteers in two positions. In the first position a vertical board was placed perpendicular to the radial border of the hand to block radial abduction, and in the second position PAST was measured without the board. Men had greater PAST. There was no difference in PAST between the dominant and non-dominant hand for both men and women, when a vertical board was used. Without the board, the values were significantly greater in the dominant hand. Radial abduction should be blocked during measurement of PAST.