Quantifying Individual Differences in the Relationship Between Intended and Actual Force Across Repeated Trials With External Feedback

Abstract

Background: Accurate force control is essential for daily and sports performance, yet individuals differ in their ability to match intended and actual force. Little is known about how external feedback influences this ability or how individual differences can be quantified. Purpose: This study examined individual differences in matching intended grip force with actual force and clarified how repeated feedback affects accuracy across force levels. Research Design: A repeated-measures design was used in which participants performed multiple trials of a perceptually guided grip force task with external feedback. Study Sample: Forty-nine healthy young men completed 11 trials at three target forces (25%, 50%, and 75% of maximum voluntary contraction). Data Collection and Analysis: Accuracy was evaluated using the absolute value of the grip error (AE). A mixed-effects model assessed fixed effects of force level and trial number and random effects reflecting individual differences in accuracy and learning rate. Results: AE decreased across trials at all force levels, indicating improved accuracy with external feedback. Improvement varied by force level: AE was initially largest and decreased most at 75%, whereas 50% showed the slowest reduction. Random-effects analysis indicated differences in the force level at which participants were most accurate, suggesting preferred control levels. In contrast, individual differences in learning rates were small. Conclusions: Individuals vary in the force levels at which they perform most accurately, yet improvement through repeated external feedback is robust. These findings advance understanding of force control and individual differences in perceptually guided motor tasks.