The general purpose of this study was to examine factors that may influence acceleration characteristics of the upper body during walking, thereby clarifying the means by which the postural system facilitates dynamic stability of the upper body during walking. Upper body accelerations were measured during a range of straight-line walking tasks. Time domain, frequency domain, signal regularity and coupling analyses were used to 1) provide new insight into gait-related upper body accelerations

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... ing walking in normal healthy adults, and 2) determine how the postural system accommodates to perturbations that challenge upper body stability during walking. The specific perturbations to the postural system that were examined in the present study were the normal ageing process, changes in walking speed, and fatigue of the cervical and lumbar erector spinae. In general, the patterns of accelerations measured at the level of the head were an attenuated version of those at the lower trunk during normal walking. Power spectral analysis revealed that both the head and lower trunk in the anterior-posterior (AP) and vertical directions (VT) directions were characterised by a single peak frequency corresponding the step frequency during normal walking. However, the most notable of all attenuation profiles was the difference between accelerations of the head and lower trunk in the mediolateral (ML) direction. ML trunk accelerations were characterised by multiple low amplitude frequency peaks, which were attenuated to a single peak at the head corresponding to stride frequency. The coupling between acceleration directions was greater for the head than the lower trunk, suggesting that the postural system promotes a coordination strategy which enhances global stability of the head. Subdividing the upper body into neck and trunk segments facilitated a more comprehensive description how the gait-related oscillations are prevented from impacting on the motion of the head. Overall, acceleration amplitude, power content, and regularity [...]