Article

Changes in step width (SW), step length (SL), and/or the variability of these
parameters have been prospectively related to risk of falling. However, it is
unknown how voluntary changes in SW and SL directly alter variability and/or
dynamic stability of walking. Here, we quantified how variability and dynamic
stability of human walking changed when individuals voluntarily manipulated SW
and SL. 14 unimpaired, young adults walked on a treadmill at their preferred
walking speed with normal gait, with a metronome and with narrower, wider,
shorter and longer steps than normal. Taking narrower steps caused increased SL
variability while mediolateral (ML) movements of the C7 vertebra (i.e., trunk)
became locally more stable (p<0.05) and anterior-posterior (AP) C7 movements
became locally less stable (p<0.05). Taking wider steps caused increased SW and
SL variability, while ML C7 movements became both locally and orbitally less
stable (p<0.05). Any change in SL caused increased SW, SL, and stride time
variability. When taking shorter steps, ML C7 movements exhibited greater
short-term local and orbital instability, while AP C7 movements exhibited
decreased short-term and long-term local instability (p<0.05). When taking longer
steps, AP, ML, and vertical C7 movements all exhibited increased long-term local
instability and increased orbital instability (p<0.05). Correlations between mean
SW, SL and dynamic stability of C7 marker motions were weak. However, short-term
voluntary changes in SW and SL did significantly alter local and orbital
stability of trunk motions.
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