Article

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. METHODS: 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. RESULTS: 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. DISCUSSION: 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.
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Langue : ANGLAIS