Characterizing the determinants of limb preference for compensatory stepping in healthy young adults

Compensatory stepping responses are frequently observed following postural perturbations. Compensatory steps require extremely rapid onset timing while maintaining sophisticated control of limb placement. However, the influence of asymmetric limb loading on compensatory stepping limb preference and step characteristics is unknown. The purpose of this study was to gain an understanding of the factors that influence limb preference for compensatory stepping under symmetric and asymmetric loading.

Ten healthy young individuals (mean age 24±3 years) experienced postural perturbations delivered using a lean-and-release system. Perturbations were delivered during three different loading conditions: (1) symmetric stance, (2) asymmetric stance with 30-70% body weight over the preferred limb and, (3) asymmetric stance with the unloaded (30% body weight) limb constrained. Kinematic and kinetic data were collected from three force plates mounted in the platform and a three-dimensional motion analysis system.

As stance loading on the preferred limb increased, step frequency with the preferred limb decreased. Forced stepping with the preferred limb loaded at 70% body weight resulted in shorter (p=0.005) and more laterally displaced (p<0.001) steps as well as non-significant trends towards faster swing time (p=0.057) and shorter time to foot-off (p=0.081) compared to steps taken from symmetric stance.

Healthy young adults prefer to step with the more unloaded limb. However, when forced to step with an asymmetrically vertically loaded limb, individuals demonstrate a number of spatio-temporal characteristics that may indicate increased instability.