Influence of a visual-verbal Stroop test on standing and walking performance of older adults.

The dual task (DT) paradigm has been used to investigate decrements in balance performance while walking and standing in fall prevention studies with older adults. However, there are inconsistent findings whether balance performance decreases or increases in DT situations. Following different theoretical models (e.g. limited resource hypothesis or cross domain competition model), these inconsistent findings can be explained by task settings and task complexity. We compared DT performance in an executive control task (Stroop test) while standing and walking to analyze which theoretical model would fit our data best. Twenty-eight persons (>65 years) were examined under single task (ST) and DT conditions for standing (sway length and sway velocity) and walking (step length, step width (SW), peak forces of the heel, mid- and forefoot). SW increased from ST to DT conditions, and step length decreased significantly. Maximum forces of the forefoot were reduced whereas the maximum forces of the midfoot increased. Additionally, correct answers of the Stroop test decreased from the ST baseline condition to DT walking. No correlations were found between DT costs (performance decrements) of standing and walking. For both conditions (standing and walking), the limited resources hypothesis fits best. Moreover, not all modified gait variables could be defined as negative DT costs. Increased SW and decreased step length might be used to compensate influences on lateral stability while demands on motor-cognitive resources increase. Further, drawing conclusions from a standing task for walking conditions might lead to misinterpretations.