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Medio lateral sway and afferent input in quiet stance

Medio lateral sway and afferent input in quiet stance

Climent, Guillaume and Goss-Sampson, Mark ORCID: 0000-0002-2662-559X (2003) Medio lateral sway and afferent input in quiet stance. In: Conference of the International Society for Postural and Gait Research - ISPGR World Congress, 23-27 March 2003, Sydney, Australia. (Unpublished)

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Introduction: Decreased medio-lateral (ML) movements following increase of the stance width was hypothesized to be the result of both a mechanical and a sensory event where activation of the proprioceptors located in the muscles and the joints of the hips increased the afferent input to the postural control system (Day et al., 1993). This study investigated the effects of decreasing the stance width on medio-lateral sway and its role in postural control in a group of young healthy females (n = 8).

Methods: Using kinetic and kinematic analysis, the following sway variables were acquired: centre of pressure (CoP) and centre of gravity (CoG) sway area, amplitude, power and frequency. Cross correlation analysis was conducted on CoP and CoG signals. Stabilogram-diffusion analysis (Collins and De Luca 1993) was also performed on CoP displacements. Measurements were performed both with eyes open and eyes closed. Two stance widths were used, a pelvic stance (PS) which was determined by the distance between the subject’s ASIS and a narrow stance (NS) being half of the PS.

Results: Independently of the visual condition, narrowing of the stance width significantly (P<0.05) altered the ML component of all the sway parameters. In stabilogram diffusion analysis, the diffusion coefficients, which represent the subject’s average level of postural sway, were increased in the ML direction. Increase in the ML scaling exponents was only seen in the short-term region i.e., the CoP tendency to move away from some relative equilibrium point increased. This was reflected by the increase in the ML critical mean square displacement indicating that CoP had to travel a greater distance before the postural system switched from an open to closed loop control. Larger CoP and CoG ML sway amplitude were also observed. Finally, the only decrease observed in the ML direction originated from the CoP and CoG sway frequency.

Discussion and Conclusions: Using similar stance width to NS, studies investigating the effects of perception of threat on postural control during quiet stance found that the amplitude of CoP displacement decreased and frequency of CoP increased linearly as postural threat increased with increasing height. It was hypothesised that the central nervous system progressively tightened its control of posture as postural threat increased (Adkin et al., 2000). These results were exactly opposite to ours. This demonstrate that upon narrowing of the stance width from PS to NS and under the safe postural condition of the present study the CoG was allowed to travel over a greater distance in the ML direction since there was no perceived postural threat. It is suggested that the postural control system produced a strategy which led to further displacements in the ML direction of the CoG as a means to acquire more proprioceptive information from the hip joints and hip muscles. With eyes closed, such a strategy was further used as the need for somatosensory input became even more important.

Item Type: Conference or Conference Paper (Poster)
Uncontrolled Keywords: Quiet stance sway
Subjects: Q Science > QM Human anatomy
Faculty / School / Research Centre / Research Group: Faculty of Education, Health & Human Sciences > School of Human Sciences (HUM)
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Last Modified: 09 Oct 2021 04:46

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