Contributions of the thumb and index finger to tip pinch force sense

This study aimed to examine the roles that the index finger and thumb play in tip pinch force sense at different force levels in both males and females. Forty-two healthy participants (21 females and 21 males) underwent an ipsilateral force reproduction assessment employing three different fingers (thumb, index finger, and tip pinch) at 3 distinct forces of 5, 10, and 20% of maximal voluntary isometric contraction (MVIC). The findings revealed no significant between incorrect (absolute error) or consistent (variable error) force sense errors among the pinch, thumb, and index finger. The results further revealed significant correlations between the pinch and index finger of a constant error at 5%, 10%, and 20% MVIC (r = 0.460, P = 0.036; r = 0.735, P < 0.001; r = 0.839, P < 0.001, respectively) in males. Significant correlations were also observed in females between the pinch and thumb of a constant error at 5%, 10%, and 20% MVIC (r = 0.436, P = 0.048; r = 0.464, P = 0.034; r = 0.565, P = 0.008, respectively). These findings demonstrated that when the thumb and index finger are employed simultaneously (tip pinch), females rely more on the thumb, while males rely more on the index finger for accurate pinching forces. A higher force level led to a higher contribution of the individual finger (thumb for females and index finger for males) to the pinch force sense.