A Novel Method to Quantify Individual Limb Contributions to Standing Postural Control.

BACKGROUND:Understanding individual limb contributions to standing postural control is valuable when evaluating populations with asymmetric function (e.g., stroke, amputations). We propose a method of quantifying three contributions to controlling the net anteroposterior center of pressure (CoP) during quiet standing: CoP moving under left and right limbs and weight shifting between the two limbs. RESEARCH QUESTION:Can these contributions to standing postural control be quantified from CoP trajectories in neurotypical adults? METHODS:Instantaneous contributions can be negative or larger than one, and integrated contributions sum to equal one. Proof-of-concept demonstrations validated these calculated contributions by restricting CoP motion under one or both feet. We evaluated these contributions in 30 neurotypical young adults who completed two (eyes opened; eyes closed) 30-s trials of bipedal standing. We evaluated the relationships between limb contributions, self-reported limb dominance, and between-limb weight distributions. RESULTS:All participants self-reported as right-limb dominant; however, a range of mean limb contributions were observed with eyes opened (Left: mean [range] = 0.52 [0.37-0.63]; Right: 0.48 [0.31-0.63]) and with eyes closed (Left: 0.51 [0.39-0.63]; Right: 0.49 [0.37-0.61]). Weight-shift contributions were small with eyes opened (0.00 [-0.01 to 0.01]) and eyes closed (0.00 [-0.01 to 0.02]). We did not identify any between-limb differences in contributions when grouped by self-reported limb dominance (p > 0.10, d < 0.31). Contributions did not significantly correlate with Waterloo Footedness scores (-0.22 < r < 0.21, p > 0.25) or between-limb weight distributions (0 < r < 0.24, p > 0.20). SIGNIFICANCE:Across neurotypical participants, we observed a notable range of limb contributions not related to self-reported limb dominance or between-limb weight distributions. With this tool, we can characterize differences in the amount of CoP motion and the underlying control strategies. Changes in limb contribution can be measured longitudinally (i.e., across rehabilitation programs, disease progression, aging) representative of limb function, which may be particularly useful in populations with asymmetric function.