Single task and dual task gait: In which condition do we walk more automatically? Answer changes with maturation

Introduction: In a recent work the complexity of gait, assessed through Sample Entropy (SE), was suggested as an innovative and relevant parameter for characterizing the maturation of gait during growth [1]. A possible physiological interpretation of this index is that it describes the amount of cognitive input during walking: in the work by Lamoth et al. [2], SE showed larger values in elderly individuals during dual task (DT), indicating that changes in cognitive functions contribute to changes in gait stability and automaticity. On the other hand, in another study on adolescents’ gait, gait complexity was found to be slightly reduced during DT gait when compared to single task (ST) gait [3]: it was suggested that, probably, adolescents use a different strategy when walking in DT conditions when compared to elderlies. The aim of this work was to further investigate how gait automaticity, assessed through SE, changes through maturation when comparing ST and DT conditions. To this purpose, SE was applied on trunk acceleration data collected during gait of subjects at different ages, from scholar children to young adults. Methods: Forty healthy subjects participated in the study: ten 7-year-old children (7YC), ten 9-year-old children (9YC), ten 15-year-old adolescents (15YC) and ten 25-year-old adults (25YA). Measures of acceleration of the trunk (at L5 level) were collected using one tri-axial wireless inertial sensor. The participants were asked to walk at self-selected speed in ST and cognitive DT conditions: the cognitive DT consisted in counting backward aloud by n from a random starting number (n was fixed at 3 for children, 8 for adolescents and 7 for young adults). For each participant 20 strides were analysed. SE (m = 2, r = 0.2 and τ = 6) was calculated on raw unfiltered data of L5 acceleration along the anteroposterior (AP), vertical (V) and mediolateral (ML) axis, for both conditions (SEap, SEv and SEml). The difference between SE in DT and ST was calculated for each participant (ΔSE). ΔSE was expressed in percentage of SE in ST. Median (and 25th and 75th percentiles) were obtained for each group. Results: Children and adolescents showed a decrease in complexity from ST to DT condition on all the three axes. Young adults showed an opposite trend on AP and ML directions (Fig. 1). ΔSE (%) results for the three axes (median, 25th and 75th percentiles) Download high-res image (94KB)Download full-size image Fig. 1. ΔSE (%) results for the three axes (median, 25th and 75th percentiles). Discussion: The results of this study suggest that the strategy used while walking during DT is different in childhood and adulthood. Adults’ results are in agreement with those shown by elderlies [2], where gait complexity in AP increased with DT, suggesting a decrease in automaticity. Children’ and adolescents’ results showed an opposite behaviour: it could be argued that they involve a lower amount of cognitive input in walking, when focusing on a cognitive task. These results highlight the relevance of studying movement performance during growth in order to improve our understanding on motor control and its development: future research will have to focus on the interpretation of these results, with particular attention on how physical and cognitive changes affect motor development.