Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC228
Static postural after-effect of stepping on a rotating treadmill
C. J. Osler1, R. F. Reynolds1
1. School of Sport and Exercise Sciences, University of Birmingham, Birmingham, United Kingdom.
The adaptive nature of the somatic sensorimotor system has been shown in the control of locomotion using a circular treadmill (Gordon et al., 1995). Following a period of stepping in place on a rotating surface, subjects turn in circles when asked to step in place on a stationary surface with eyes closed (Weber et al., 1998). It is likely a remodelling of the relationship between the trunk and feet occurs, primarily mediated by somatic information. It has been suggested that the effects on dynamic locomotion may partly be caused by a reorganisation of static posture, namely, head and trunk rotation over the feet (Hollands et al., 2007). Here, we further investigated this postural after-effect; our aim was to ascertain its magnitude and at what level of the body it occurs. The adaptation protocol consisted of stepping in the centre of a turntable rotating at 60°/sec. Participants (n=6) were required to step at a cadence of 100steps/min for 20min. Equal numbers of subjects experienced clockwise and anti-clockwise rotations. Yaw of the head and trunk relative to the feet were measured over a 60sec period pre- and post- adaptation. Subjects were instructed to stand facing their perceived straight ahead, with feet together and eyes closed. The results show subjects demonstrated a significant change in the magnitude of actual head yaw (ΔHY) and trunk yaw (ΔTY) post-adaptation (mean ± SD: ΔHY 19.7 ± 7.6°, ΔTY 14.1± 5.3°; one-sample t-tests: both p=0.001). There was no significant difference in the magnitude of the after-effect between clockwise and anti-clockwise rotations (independent-samples t-tests: ΔHY p=0.853, ΔTY p=0.742). This confirms static posture is altered as a result of stepping on the rotating turntable. When studying the level at which the post-adaptation yaw occurs, results show that ΔTY accounted for 71.5% of ΔHY. This suggests the majority of the adaptation takes place below the level of the trunk. This most likely occurs at the hips, due to a remodelled relationship between the upper body and the feet. It also appears to result in an altered perception of “straight-ahead”. This after-effect in static posture could be used to investigate how an altered head-on-feet orientation is integrated with other sensory channels for the control of posture.
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