Abstract
Head stabilization is fundamental for balance during locomotion but can be impaired in elderly or diseased populations. Previous studies have identified several parameters of head stability with possible diagnostic value in a laboratory setting. Recently, the ecological validity of measures obtained in such controlled contexts has been called into question. The aim of this study was to investigate the ecological validity of previously described parameters of head stabilization in a real-world setting. Ten healthy subjects participated in the study. Head and trunk movements of each subject were recorded with inertial measurement units (IMUs) for a period of at least 10 h. Periods of locomotion were extracted from the measurements and predominant frequencies, root mean squares (RMSs) and bout lengths were estimated. As parameters of head stabilization, attenuation coefficients (ACs), harmonic ratios (HRs), coherences, and phase differences were computed. Predominant frequencies were distributed tightly around 2 Hz and ACs, HRs, and coherences exhibited the highest values in this frequency range. All head stability parameters exhibited characteristics consistent with previous reports, although higher variances were observed. These results suggest that head stabilization is tuned to the 2 Hz fundamental frequency of locomotion and that previously described measures of head stability could generalize to a real-world setting. This is the first study to address the ecological validity of these measures, highlighting the potential use of head stability parameters as diagnostic tools or outcome measures for clinical trials. The low cost and ease of use of the IMU technology used in this study could additionally be of benefit for a clinical application.
Highlights
During locomotion, reflexive head movements operate to minimize horizontal head translation (Cromwell et al, 2001a; Mazzà et al, 2009) and simultaneously compensate for vertical translation by pitching the head (Pozzo et al, 1990; Hirasaki et al, 1999)
A convenience sample of ten healthy human subjects with no history of balance or gait disorders participated in the experiment
In order to make our results comparable to previously published results, we limited our analysis to segments with head predominant frequencies between 1 and 2.6 Hz, corresponding to the range of frequencies associated with walking speeds between 0.6 and 2.2 m/s determined in Hirasaki et al (1999)
Summary
Reflexive head movements operate to minimize horizontal head translation (Cromwell et al, 2001a; Mazzà et al, 2009) and simultaneously compensate for vertical translation by pitching the head (Pozzo et al, 1990; Hirasaki et al, 1999). These stabilization behaviors are thought to be crucial for effective control of both balance and locomotion because they reduce undesired variability of vestibular and visual sensory inputs (Pozzo et al, 1990). Known as ecological momentary assessment (EMA) (Shiffman et al, 2008), advocates the sampling of clinically relevant parameters in a subject’s natural environment rather than a clinical setting
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