Dataset Information

Swaying slower reduces the destabilizing effects of a compliant surface on voluntary sway dynamics.

ABSTRACT: The ability to control weight shifting (voluntary sway) is a crucial factor for stability during standing. Postural tracking of an oscillating visual target when standing on a compliant surface (e.g. foam) is a challenging weight shifting task that may alter the stability of the system and the muscle activation patterns needed to compensate for the perturbed state. The purpose of this study was to examine the effects of surface stability and sway frequency on the muscle activation of the lower limb, during visually guided voluntary postural sway. Seventeen volunteers performed a 2-min voluntary sway task in the anterior-posterior direction following with their projected center of pressure (CoPAP) a periodically oscillating visual target on a screen. The target oscillated at a frequency of 0.25 Hz or 0.125 Hz, while the participants swayed on solid ground (stable surface) or on a foam pad (unstable surface), resulting in four experimental conditions. The electromyogram (EMG) of 13 lower limb muscles was measured and the target-CoPAP coupling was evaluated with coherence analysis, whereas the difference in the stability of the system between the conditions was estimated by the maximum Lyapunov exponent (MLE). The results showed that slower oscillations outperformed the faster in terms of coherence and revealed greater stability. On the other hand, unstable ground resulted in an undershooting of the CoPAP to the target and greater MLE. Regarding the EMG data, a decreased triceps surae muscle activation at the low sway frequency compared to the higher was observed, whereas swaying on foam induced higher activation on the tibialis anterior as well. It is concluded that swaying voluntarily on an unstable surface results in reduced CoPAP and joint kinematics stability, that is accomplished by increasing the activation of the distal leg muscles, in order to compensate for this perturbation. The reduction of the sway frequency limits the effect of the unstable surface, on the head and upper body, improves the temporal component of coherence between CoP and target, whereas EMG activity is decreased. These findings might have implications in rehabilitation programs.

SUBMITTER: Patikas DA

PROVIDER: S-EPMC6905565 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Swaying slower reduces the destabilizing effects of a compliant surface on voluntary sway dynamics.

Patikas Dimitrios A DA Papavasileiou Anastasia A Ekizos Antonis A Hatzitaki Vassilia V Arampatzis Adamantios A

PloS one 20191211 12

The ability to control weight shifting (voluntary sway) is a crucial factor for stability during standing. Postural tracking of an oscillating visual target when standing on a compliant surface (e.g. foam) is a challenging weight shifting task that may alter the stability of the system and the muscle activation patterns needed to compensate for the perturbed state. The purpose of this study was to examine the effects of surface stability and sway frequency on the muscle activation of the lower l ...[more]

PMID: 31826026

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Project description:ObjectivesSlowed speaking rate was examined for its effects on speech intelligibility, its interaction with the benefit of contextual cues, and the impact of these factors on listening effort in adults with cochlear implants.DesignParticipants (n = 21 cochlear implant users) heard high- and low-context sentences that were played at the original speaking rate, as well as a slowed (1.4× duration) speaking rate, using uniform pitch-synchronous time warping. In addition to intelligibility measures, changes in pupil dilation were measured as a time-varying index of processing load or listening effort. Slope of pupil size recovery to baseline after the sentence was used as an index of resolution of perceptual ambiguity.ResultsSpeech intelligibility was better for high-context compared to low-context sentences and slightly better for slower compared to original-rate speech. Speech rate did not affect magnitude and latency of peak pupil dilation relative to sentence offset. However, baseline pupil size recovered more substantially for slower-rate sentences, suggesting easier processing in the moment after the sentence was over. The effect of slowing speech rate was comparable to changing a sentence from low context to high context. The effect of context on pupil dilation was not observed until after the sentence was over, and one of two analyses suggested that context had greater beneficial effects on listening effort when the speaking rate was slower. These patterns maintained even at perfect sentence intelligibility, suggesting that correct speech repetition does not guarantee efficient or effortless processing. With slower speaking rates, there was less variability in pupil dilation slopes following the sentence, implying mitigation of some of the difficulties shown by individual listeners who would otherwise demonstrate prolonged effort after a sentence is heard.ConclusionsSlowed speaking rate provides release from listening effort when hearing an utterance, particularly relieving effort that would have lingered after a sentence is over. Context arguably provides even more release from listening effort when speaking rate is slower. The pattern of prolonged pupil dilation for faster speech is consistent with increased need to mentally correct errors, although that exact interpretation cannot be verified with intelligibility data alone or with pupil data alone. A pattern of needing to dwell on a sentence to disambiguate misperceptions likely contributes to difficulty in running conversation where there are few opportunities to pause and resolve recently heard utterances.

Project description:IntroductionThe effect of rhythmic acoustic stimuli on body sway is of increasing interest due to their positive contribution when training or restoring the control of movement. Inertial sensors show promise as a portable, easier, and more affordable method compared to the force plate "gold standard" concerning the evaluation of postural sway. This study examined the concurrent validity of inertially sensed measures of voluntary body sway against those obtained with a force plate, in silence and while exposed to a rhythmic acoustic stimulus.MethodsTemporal (sway duration and variability) and spatial (trajectory length, variability, range, velocity, and area) body sway variables were extracted using an inertial sensor (at L5) in synchronization with a force plate, during anteroposterior body sway in silence and while exposed to a rhythmic acoustic stimulus (n = 18 young women; two 70-s trials in each condition). Statistics included bivariate correlations between the inertially sensed and the force plate measures, separately, in silence and with a rhythmic acoustic stimulus, as well as for the effect of the rhythmic acoustic stimulus (percentage difference from silence) (p ≤ 0.05, SPSS v25.0).ResultsThe inertially sensed measures demonstrated good-to-excellent concurrent validity for all temporal and almost all spatial variables, both in silence and with rhythmic acoustic stimulus (r > 0.75, p = 0.000), as well as for the rhythmic acoustic-stimulus effect (r > 0.75, p ≤ 0.05).ConclusionThe inertially sensed measures of the voluntary anteroposterior body sway demonstrated an overall good-to-excellent concurrent validity against those obtained with the force plate "gold standard," both in the silence and the rhythmic acoustic stimulus conditions, as well as for the rhythmic acoustic-stimulus effect. The findings of this pilot study allow the recommendation of inertial sensing for the evaluation of postural control alterations when exposed to rhythmic acoustic stimuli, a condition of increasing interest due to the positive contribution of such stimuli when training or restoring the control of movement.

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Swaying slower reduces the destabilizing effects of a compliant surface on voluntary sway dynamics.

Publications

Swaying slower reduces the destabilizing effects of a compliant surface on voluntary sway dynamics.

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