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. 2015 Jul 31;10(7):e0134148.
doi: 10.1371/journal.pone.0134148. eCollection 2015.

How to Sync to the Beat of a Persistent Fractal Metronome without Falling Off the Treadmill?

Affiliations

How to Sync to the Beat of a Persistent Fractal Metronome without Falling Off the Treadmill?

Melvyn Roerdink et al. PLoS One. .

Abstract

In rehabilitation, rhythmic acoustic cues are often used to improve gait. However, stride-time fluctuations become anti-persistent with such pacing, thereby deviating from the characteristic persistent long-range correlations in stride times of self-paced walking healthy adults. Recent studies therefore experimented with metronomes with persistence in interbeat intervals and successfully evoked persistent stride-time fluctuations. The objective of this study was to examine how participants couple their gait to a persistent metronome, evoking persistently longer or shorter stride times over multiple consecutive strides, without wandering off the treadmill. Twelve healthy participants walked on a treadmill in self-paced, isochronously paced and non-isochronously paced conditions, the latter with anti-persistent, uncorrelated and persistent correlations in interbeat intervals. Stride-to-stride fluctuations of stride times, stride lengths and stride speeds were assessed with detrended fluctuation analysis, in conjunction with an examination of the coupling between stride times and stride lengths. Stride-speed fluctuations were anti-persistent for all conditions. Stride-time and stride-length fluctuations were persistent for self-paced walking and anti-persistent for isochronous pacing. Both stride times and stride lengths changed from anti-persistence to persistence over the four non-isochronous metronome conditions, accompanied by an increasingly stronger coupling between these gait parameters, with peak values for the persistent metronomes. These results revealed that participants were able to follow the beat of a persistent metronome without falling off the treadmill by strongly coupling stride-length fluctuations to the stride-time fluctuations elicited by persistent metronomes, so as to prevent large positional displacements along the treadmill. For self-paced walking, in contrast, this coupling was very weak. In combination, these results challenge the premise that persistent metronomes in gait rehabilitation would evoke stride-to-stride dynamics reminiscent of self-paced walking healthy adults. Future studies are recommended to include an analysis of the interrelation between stride times and stride lengths in addition to the correlational structure of either one in isolation.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Examples of stride-to-stride fluctuations.
Representative examples of stride-time, stride-length and stride-speed time series for two non-isochronous metronome conditions with anti-persistence (α0.2, left panel) and persistence (α0.9, right panel) in interbeat intervals. The correlation between stride-times and stride-length time series was positive, and much stronger for the persistent (r = 0.61, right panel) than for the anti-persistent (r = 0.36, left panel) metronome condition.
Fig 2
Fig 2. Scaling exponents for original and surrogate time series.
DFA scaling exponents α for stride speeds (left panel), stride times (center panel) and stride lengths (right panel) for uncued treadmill walking (UC) and isochronous (ISO) and non-isochronous (α0.2, α0.5, α0.6, α0.9) metronome conditions. DFA scaling exponents α are given for original time series (gray circles) as well as for phase-randomized and cross-correlated phase-randomized surrogates (black diamonds and white squares, respectively).
Fig 3
Fig 3. Maximal displacement and coupling strength.
Results of maximal displacement along the treadmill (left panel) and the coupling strength between stride times and stride lengths (right panel) for uncued treadmill walking (UC) and isochronous (ISO) and non-isochronous (α0.2, α0.5, α0.6, α0.9) metronome conditions.

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