# Effects of a Dual-Task Paradigm and Gait Velocity on Dynamic Gait Stability during Stair Descent
## 4 Discussion  
This work is the first known research to investigate the effect of a concurrent dual-task condition on gait velocity and DGS, represented by IA, one of the potential indicators for DGS, during stair descent. The main observations in this study were threefold. First, peak gait velocity decreased under concurrent cognitive (CT) or manual (MT) dual-task conditions. Second, DGS was adversely affected by a concurrent dual-task; and finally. Third, IA was positively related to gait velocity and negatively related to a concurrent MT. Agreeing with previous literature, the results here showed that maximum gait velocity during a single-limb stance decreased during dual-task stair descent. Previous research on the effect of dual-task paradigms during stair negotiation on DGS using the COM range of motion reported a decrease in velocity during stair descent/ascent among young males [9]. It has also been reported  
Figure 3: COM–COP inclination angles (y) of the single-support phase (x) in the (a) anterior/posterior and (b) medial/lateral directions; # Significant difference between single-task and cognitive dual-task conditions; # Significant difference between single-task and manual dual-task conditions; \(\bullet\) Significant difference between cognitive dual-task and manual dual-task conditions. that velocity decreased under dual-task conditions during level walking for both young [34] and old participants [7; 10]. Here, the maximum gait velocity was greater under ST than under CT/MT. It was once believed that gait occurs unconsciously and does not involve higher brain functions such as attentional resources. However, a consensus has been reached that CT and MT require attentional resources [9; 28; 35; 36; 37]. Under dual-task conditions, attentional resources are split and allocated to each task, and the concurrent task draws attentional resources away from gait [9]. Dual-tasks appear to cause a performance decrement in at least one of the components of the dual-task. Previous studies have indicated that dual-task changes in gait might result from a competition between the attention demands of gait and the concomitant dual-task [30]. This study corroborates previous findings that a dual-task paradigm affected gait velocity. Although the paradigms were observed to influence gait velocity adversely, this does not mean that they would negatively influence DGS evaluated as IA. IA was hypothesized to be adversely affected by CT/MT when compared to ST. However, our results failed to support our second hypothesis in both the anterior/posterior and medial/lateral directions; the decreased IA indicates improved DGS under CT or MT conditions during stair descent. These results are consistent with most previous young participant research, which reported additional stabilization rather than postural destabilization occurring during a concurrent dual-task paradigm [12; 13; 37; 38]. One study was reported that showed worse DGS under dual-task conditions among young males in terms of COM medial/lateral range of motion [9]. The differences between our study and theirs may stem from the different DGS measurements. Their dependent variable was the COM range of motion, which does not necessarily indicate instability [19]. The unique effects of dual-tasks on DGS should be studied without the influence of gait velocity. Thus, stepwise forward elimination multiple regression analyses were performed to determine and compare the relationships between velocity, dual-task condition, and DGS. The third hypothesis was supported since the results showed that DGS decreased with increasing gait velocity under both the MT and CT paradigms. Two previous studies published by our group reported that IA was increased under a relatively faster velocity condition during over-ground [18] and treadmill walking [20]. The regression analyses also indicated that concurrent MT decreased IA in the anterior/posterior direction with a magnitude of 0.768\({}^{\circ}\), which means that concurrent MT increases DGS.