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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Mique Saes (VU university medical center)
Mohamed Irfan Mohamed Refai (University of Twente)
Ilona Visser (VU university medical center)
Peter Veltink (University of Twente)
Jaap Buurke (Roessingh Research and Development)
Hans Bussmann (Erasmus MC Rotterdam)
Gert Kwakkel (VU university medical center)
Bert-Jan van Beijnum (University of Twente)
Erwin van Wegen (VU university medical center)
Carel Meskers (VU university medical center)

Abstract:
Background Many stroke patients suffer from distorted gait patterns. Previous research show that the Margin of Stability (MoS), defined as the shortest distance between the projection of the extrapolated center of mass (XCoM) and the Base of Support (BoS)(Hof et al., 2008), is a potential relevant metric that varies with different balance impairment levels (Van Meulen et al. 2006; Bruijn et al., 2013). However, the influence of different gait patterns on MoS is not yet systematically explored. We investigated the influence of casting induced asymmetry and changes in walking speed on MoS in healthy individuals, which can be used to understand compensatory strategies and ultimately gait recovery post stroke. Methods Eight healthy participants walked at different speeds (0.4m/s, 0.8m/s, 1.2m/s and preferred speed), under two conditions: with and without a complete restriction of the dominant ankle using plaster casting. Kinematic gait measurements were performed on a GRAIL treadmill system (Motek, Inc.) including force platforms and ten infrared cameras. MoS was calculated in anterior-posterior (MOSAP) and mediolateral (MOSML) direction (van Meulen et al., 2016) at initial contact of the right and left foot separately. Results MoSAP and MoSML increased with gait speed (p<0.001). Step length of the restricted foot was smaller when walking at >0.8m/s compared to the non-restricted condition (p<0.05). MoSAP was further outside the BoS in casted compared to unrestricted condition at 0.8m/s (p<0.05). MoSAP is outside the BoS at 0.8m/s or faster. Casting resulted in increased MoSML towards the restricted side (p<0.001). This increase was correlated with the increase in step width (r=0.74,p=0.04). Conclusion MoS changes with gait speed and asymmetry. The shift of MoS to the casted side is probably caused by an increased step width. Healthy individuals are able to keep their XCoM outside their BoS in AP direction with unilateral casting of the ankle joint, compensation strategies in stroke patients are probably different. Significance MoS is responsive to asymmetrical walking patterns and changes in gait speed. MoS might be a candidate metric to detect changes and progress in stroke rehabilitation during gait.