Locomotor behaviour of children while navigating through apertures

Abstract

During everyday locomotion, we encounter a range of obstacles requiring specific motor responses; a narrow aperture which forces us to rotate our shoulders in order to pass through is one example. In adults, the decision to rotate their shoulders is body scaled (Warren and Whang in J Exp Psychol Hum Percept Perform 13:371–383, 1987), and the movement through is temporally and spatially tailored to the aperture size (Higuchi et al. in Exp Brain Res 175:50–59, 2006; Wilmut and Barnett in Hum Mov Sci 29:289–298, 2010). The aim of the current study was to determine how 8-to 10-year-old children make action judgements and movement adaptations while passing through a series of five aperture sizes which were scaled to body size (0.9, 1.1, 1.3, 1.5 and 1.7 times shoulder width). Spatial and temporal characteristics of movement speed and shoulder rotation were collected over the initial approach phase and while crossing the doorway threshold. In terms of making action judgements, results suggest that the decision to rotate the shoulders is not scaled in the same way as adults, with children showing a critical ratio of 1.61. Shoulder angle at the door could be predicted, for larger aperture ratios, by both shoulder angle variability and lateral trunk variability. This finding supports the dynamical scaling model (Snapp-Childs and Bingham in Exp Brain Res 198:527–533, 2009). In terms of movement adaptations, we have shown that children, like adults, spatially and temporally tailor their movements to aperture size.

Appendix

Safety margins were calculated by determining the relative distance between the shoulders as the participant moved through the door. The difference between this and the aperture size was taken to be the safety margin. Values were then normalised to shoulder width of the participant. Safety margins were only calculated for turn trials. The exclusion of no turn trials meant that safety margins were not calculated from a full data set. For adults, the 1.3 SA ratio safety margin was calculated for 7 out of 9 participants, and the 1.5 and 1.7 SA ratio could not be calculated. For children, safety margins for the 1.3 SA ratio included all children, the safety margin for the 1.5 SA ratio included 14 children and the safety margin for the 1.7 SA ratio included 4 children. Due to this loss of data, we will only compare safety margins for the 0.9, 1.1 and 1.3 SA ratio. It was not possible to combine the safety margins for the five SA ratios as variance was seen for both adults and children.

To investigate whether normalised safety margins were different across adults and children, we carried out independent samples t-tests (group) and found a significant effect of group for 0.9 SA ratio [t(23) = −2.336 P = 0.029] and an approaching significant effect for 1.1 SA ratio [t(23) = −1.815 P = 0.083]. The difference between adults and children suggests that even when shoulder width has been taken into account there is a difference between adults and children in terms of the safety margin left for the 0.9 and 1.1 SA ratio, this supports the Snapp-Childs and Bingham (2009) data. To further investigate the relationship between safety margins and movement variability, regression analyses were carried out between safety margins and the variability of safety margins. Neither the 0.9 nor the 1.1 SA ratio End wall showed a significant regression analysis.