Gait speed and postural stability during stair negotiation: effects of dual task and postural task difficulty

Introduction Dual task interference occurs when the introduction of a secondary task during a cognitive or motor performance leads to a competition between the attentional resources available, resulting in a decreased performance in either task. The attentional demands of a task and the interference effects of concurrent tasks are influenced by several factors, such as subject's age, skill level, task difficulty and the nature of the tasks involved (Woollacott and Shumway-Cook 2002). Two different types of secondary tasks, a mental task and a manual task, have been used in dual task studies (Woollacott and Shumway-Cook 2002; Asai, Misu et al. 2014). However, most postural control studies only address dual-task interference with an extra mental task. It is interesting to investigate dual-task interference in the context of more complex postural tasks, such as stair negotiation. We study how secondary mental and manual tasks interfere with stair negotiation and how attention is allocated between tasks when a person concurrently performs tasks with different levels of complexity. Methods Gait kinematic parameters and secondary task performance were obtained from fifteen normal subjects while ascending and descending a four-step staircase at three inclinations (17.7°, 29.4°, and 41.5°) as well as level walking. They performed a mental task, ‘backward digit recall’ (Maylor and Wing 1996), a manual task, ‘holding a cup of water’ and a combination of the two tasks concurrently. Kinematic data was recorded by a 14-camera three-dimensional motion capture system and kinematic data of the lower extremities as well as the body COM were collected by using the Plug-in gait model. Gait performance was measured by gait speed. Postural stability was assessed by CoM RoMs in medial-lateral (ML-COM RoM) and anterior-posterior (AP-COM RoM) directions, separately. Also, the performance of each secondary task was measured. Two-way repeated measures of ANOVA was performed for gait speed and CoM RoMs as well as for secondary task performance. Results In mental and manual tasks, no significant main effect of postural task was observed. In contrast, results for gait speed and COM RoMs showed a significant main effect of postural task and secondary task (p<0.05). There also was a significant effect of postural task by secondary task interaction in gait speed (p<0.001). However, no interaction effect was found in results for COM RoMs. Overall, increasing difficulty of postural tasks and secondary tasks lead to decreased gait speed and increased AP-COM RoM. No systematic change was observed in ML-COM RoM. Discussion Postural tasks did not have an effect on performance of the secondary tasks. The secondary tasks did however affect gait speed and postural stability: more complex secondary tasks compromise the postural stability and decrease the gait speed. When there is competition between two motor tasks, one of which is postural control, the maintenance of stability has priority. Method and results of this study can be used to evaluate postural stability and gait in order to predict a possible fall. Also, our results are useful for improving rehabilitation and treatment procedures where the relationship between attention demands and the control of posture and gait is important. Acknowledgements. This work is supported by the Dutch research project COMMIT - Virtual Worlds for Well-Being. References Asai, T., S. Misu, et al. (2014). Gait & posture 39(1): 54-59. Maylor, E. A. and A. M. Wing (1996). The Journals of Gerontology Series B: Psychological Sciences and Social Sciences 51(3): P143-P154. Woollacott, M. and A. Shumway-Cook (2002). Gait & posture 16(1): 1-14.