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Two independent contributions to step variability during over-ground human walking.

Collins SH, Kuo AD - PLoS ONE (2013)

Bottom Line: We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01).The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations.Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering and Robotics Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.

ABSTRACT
Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control.

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Difference in step length and width variability between walking with eyes open and eyes closed.(A) Eyes open. (B) Eyes closed. Each panel shows total variance of step length and width (left and right bars of each pair), speed-related length and width components, and filtered length and width components. When walking with eyes closed, subjects walked with 56% greater step length variance, and 103% greater step width variance (P < 0.05). Speed-related trends do not account for the increased gait variability with eyes closed.
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pone-0073597-g005: Difference in step length and width variability between walking with eyes open and eyes closed.(A) Eyes open. (B) Eyes closed. Each panel shows total variance of step length and width (left and right bars of each pair), speed-related length and width components, and filtered length and width components. When walking with eyes closed, subjects walked with 56% greater step length variance, and 103% greater step width variance (P < 0.05). Speed-related trends do not account for the increased gait variability with eyes closed.

Mentions: Walking with eyes closed had relatively little effect on average steps, and much greater effect on step variability (Figure 5). Subjects walked with slightly reduced average step lengths and speeds, with reductions of 3.8% and 4.5%, respectively (P < 0.05). But both eyes open and closed trials were consistent with the same preferred step length relationship, that is, with no significant differences in α and β (P = 0.36 and P = 0.17, respectively). Mean step width exhibited a non-significant increase of 6.4% (P = 0.09). The greatest effect of the eyes closed condition was on the step variabilities with the speed-related trends excluded. There was a 103% increase in de-trended step width variability (P = 5.7 · 10−6), and about half that increase, 56% in de-trended step length variability (P = 0.001).


Two independent contributions to step variability during over-ground human walking.

Collins SH, Kuo AD - PLoS ONE (2013)

Difference in step length and width variability between walking with eyes open and eyes closed.(A) Eyes open. (B) Eyes closed. Each panel shows total variance of step length and width (left and right bars of each pair), speed-related length and width components, and filtered length and width components. When walking with eyes closed, subjects walked with 56% greater step length variance, and 103% greater step width variance (P < 0.05). Speed-related trends do not account for the increased gait variability with eyes closed.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3756042&req=5

pone-0073597-g005: Difference in step length and width variability between walking with eyes open and eyes closed.(A) Eyes open. (B) Eyes closed. Each panel shows total variance of step length and width (left and right bars of each pair), speed-related length and width components, and filtered length and width components. When walking with eyes closed, subjects walked with 56% greater step length variance, and 103% greater step width variance (P < 0.05). Speed-related trends do not account for the increased gait variability with eyes closed.
Mentions: Walking with eyes closed had relatively little effect on average steps, and much greater effect on step variability (Figure 5). Subjects walked with slightly reduced average step lengths and speeds, with reductions of 3.8% and 4.5%, respectively (P < 0.05). But both eyes open and closed trials were consistent with the same preferred step length relationship, that is, with no significant differences in α and β (P = 0.36 and P = 0.17, respectively). Mean step width exhibited a non-significant increase of 6.4% (P = 0.09). The greatest effect of the eyes closed condition was on the step variabilities with the speed-related trends excluded. There was a 103% increase in de-trended step width variability (P = 5.7 · 10−6), and about half that increase, 56% in de-trended step length variability (P = 0.001).

Bottom Line: We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01).The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations.Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering and Robotics Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States of America.

ABSTRACT
Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control.

Show MeSH
Related in: MedlinePlus