Date Published: June 5, 2018
Publisher: Public Library of Science
Author(s): David Conradsson, Caroline Paquette, Erika Franzén, Yih-Kuen Jan.
Medio-lateral stability during walking turns relies on the interaction between precise weight shifts of the body and changes in base of support by regulating step width. Although older adults and clinical populations often slow down while turning in order to compensate for balance impairments, little is known about the influence of walking speed on stability during turning.
To compare medio-lateral stability between walking turns and straight walking and to investigate whether walking speed affects medio-lateral stability during turning in healthy older adults.
Nineteen older adults walked straight or walked and turned 180° to the right and left at their comfortable speed and at a slow pace. The walking direction was visually cued before they started to walk (preplanned) or while walking straight (unplanned). As a proxy for medio-lateral stability, we calculated the absolute difference between pelvis lateral displacement and the lateral edge of the base of support during straight walking and turning.
Overall, irrespective of turning condition, medio-lateral stability was enhanced during turning as the pelvis was further away from the boundary of the base of support resulting in a greater margin of stability compared to straight walking. Turning at a slow pace hampered medio-lateral stability as demonstrated by pelvis lateral displacement closer to the boundaries of the base of support resulting in reduced margins of stability. The reduction in stability was caused by a narrower step width during slow walking whereas pelvis lateral displacement was unaffected by turning speed.
In older adults, medio-lateral stability was augmented during turning compared to straight walking, whereas turning at a slow pace hampered medio-lateral stability. These findings provide insights into the postural strategies used by older adults in order to adapt to the postural challenges of turning and straight walking.
Locomotion in everyday life is rarely performed during steady state walking; in fact, up to 50% of the steps executed each day incorporate turning steps . As turning naturally induces instability to the body, it challenges postural control and can cause falls and injuries among older adults [2, 3]. The high prevalence and serious consequences of falls in older adults [4, 5] highlight the importance of detecting age-related mechanisms of fall-related tasks, such as walking turns.
As illustrated in Fig 2a, for step and spin strategy, walking turns at comfortable speed were 21–22% faster during the pre- and unplanned condition compared to turning at slow speed (p < 0.001). Walking turns at comfortable speed also resulted in 4–5% greater rotation for the step strategy (p < 0.001, Fig 2b) and 6–7% greater rotation for the spin strategy compared to turning at slow speed (p < 0.001, Fig 2b). Unplanned turns resulted in 6% higher body rotation than preplanned turns (p < 0.001) whereas there were no differences in turning speed between pre- and unplanned turns (p ≥ 0.382, see Fig 2a). Walking turns at comfortable speed also revealed 12–20% longer average step length for the step strategy (preplanned: 587mm vs 668mm, p < 0.001, unplanned: 560mm vs 670mm, p < 0.001) and the spin strategy (preplanned: 592mm vs 667mm, p < 0.001, unplanned: 599mm vs 670mm, p < 0.001) compared to turning at a slow pace. Contrasting our hypothesis, we found that older adults overall augmented medio-lateral stability while turning by increasing their margins of stability compared to straight walking. On the other hand, turning at a slow pace hampered medio-lateral stability, as the pelvis was shifted closer to or outside the boundaries of BOS, which was caused solely by a narrower step width during slow turning compared to turning at a comfortable speed. Older adults enhanced their medio-lateral stability during turning (i.e. increasing their margins of stability) compared to straight walking, which might reflect an effort to compensate for the greater postural challenges associated with turning. Surprisingly, we found that medio-lateral stability during turning was hampered (i.e. pelvis lateral displacement closer to the boundary of BOS), while walking speed was reduced. This finding could reflect an appropriate adaptive strategy due to the reduced postural perturbations during slow turning compared to their comfortable walking speed. Source: http://doi.org/10.1371/journal.pone.0198455