Anticipatory and Motor Equivalence Responses of Sagittal Configuration to a Transient Volitional Task

Optimality in motor behavior is both task- and person-specific. Despite progress in theoretical models, clinical perspectives on optimal movement most commonly invoke between-subjects research findings studying imprecise constructs, and the implications for practice are far-reaching. Clarifying the theory and evidence concerning optimality in movement is essential for informed application of these nuanced concepts. We studied motor performance effects of optimality in bipedal sagittal configuration, a behavior of disputed significance in disease explanatory frameworks. Sixteen healthy young adults performed bipedal standing tasks under 2 non-optimal stance configurations (toes up, toes down) intended to induce a range of initial displacement from our surrogate for optimal (flat). Goal-equivalent variance (GEV) in joint angle displacement was quantified using an uncontrolled manifold approach. Bipedal standing was periodically interrupted by "mini-squats", around which we quantified the effects of proximity to optimal configuration on 1) motor equivalent (ME) deviation pre-to-post squat, and 2) anticipatory GEV constriction. Toes-up stance was associated with greater pre-to-post squat ME deviation and greater anticipatory GEV constriction, both consistent with greater initial displacement from optimality. These observations partially support our hypothesis that bipedal sagittal configuration is subject to optimality, which informs ongoing debates concerning the role of movement optimality in health and disease.