Leg choice for volitional goal-directed stepping is primarily influenced by effort rather than success: A preliminary investigation in neurotypical adults

During reaching, arm choice depends on success and motor effort. Whether these factors influence leg choice for stepping behavior is unknown. Here, we conducted two experiments (1: proof-of-principle; 2: kinematic analysis) to explore whether limb selection for goal-directed stepping depends on success and/or effort under two Choice conditions: Free (choose either leg) and Constrained (no choice – only left leg). For both experiments, in which Free trials always preceded Constrained trials, we adapted the classic center-out target array in which right-leg dominant neurotypical adults stood in the middle of the array and stepped to pre-cued targets as accurately as possible. The Free condition reflected the preferred limb choice. We compared success, effort, and self-perceived difficulty between Free and Constrained trials, separately for three (Experiment 1) and two (Experiment 2) regions. Overall, in Free condition, participants uniformly selected the limb ipsilateral to lateral left and right targets and with slight leg dominance-based bias for central targets. Success (step accuracy and consistency/precision) did not depend on Choice condition, rather, performance improved over repeated trials. Effort (peak vertical foot lift and step path ratio) depended on Choice condition. Finally, independent of Choice condition, participants perceived posterior targets (particularly far targets) as the most difficult during non-dominant left steps. Present findings suggest that effort may influence leg choice to a greater degree than success for goal-directed stepping. Future work that probes these findings’ robustness in patients with unilateral paresis (intrinsic constraint) may advance our understanding of the motor decision processes for goal-directed mobility behaviors.