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

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.

Increased gait variability may not imply impaired stride-to-stride control of walking in healthy older adults

“…This fundamentally dynamical analysis of movement fluctuations near the GEM yields a quantification of the “strength” of motor regulation (i.e., control) that is independent of the amount of variability present in the data [21, 22]. Our models of stride-to-stride fluctuation dynamics were validated experimentally [24, 25] and our overall theoretical predictions replicated in at least three independent studies [26–28]. …”

Fractal Fluctuations in Human Walking: Comparison Between Auditory and Visually Guided Stepping

“…Rev2, Feb. 2016 time and stride length are actually cross-correlated: 7,34,41 In other words, stride time and stride length vary over time in a similar way (positive correlations). 34 A model that explains how motor control manages speed regulation has been proposed by Dingwell and collaborators.…”

“…Whereas treadmill walking has only a marginal effect on the fractal fluctuation of stride time compared to overground walking, 4,39 treadmill walking changes the serial correlations of stride speed into anti-correlations, as AC does for stride time. 8,34,41 Moreover, when AC is combined with treadmill walking, all the gait parameters (stride time, stride length, and stride speed) exhibit anti-correlated patterns. 34,41 The constant speed Author's accepted version of the treadmill (speed cueing) requires coordinated adjustments between the stride time and the stride length to maintain an appropriate speed and thus avoid falling off the treadmill.…”

“…8,34,41 Moreover, when AC is combined with treadmill walking, all the gait parameters (stride time, stride length, and stride speed) exhibit anti-correlated patterns. 34,41 The constant speed Author's accepted version of the treadmill (speed cueing) requires coordinated adjustments between the stride time and the stride length to maintain an appropriate speed and thus avoid falling off the treadmill. As a result, when cadence and speed are voluntarily adjusted to external cues (dual cueing), stride length must be coordinated accordingly (the "loss of redundancy" paradigm).…”

“…As a result, when cadence and speed are voluntarily adjusted to external cues (dual cueing), stride length must be coordinated accordingly (the "loss of redundancy" paradigm). 8,34,41 In addition to the temporal adjustments of steps to auditory cues, another possible type of sensorimotor synchronization consists of adjusting step length to visual cues (hereafter referred to as visual cueing, VC). In this case, a walker anticipates the position of his or her next step to coincide with a mark on the floor.…”