Objectives: The study of spatial-temporal parameters and their changes in walking with dual tasks, symmetry in right and left legs functions as well as changes in these parameters have received scant attention from researchers. Therefore, the purpose of this study was to evaluate the changes in spatial-temporal parameters of walking due to their simultaneous execution with cognitive dual-task in older people with impaired balance.
Methods & Materials: Thirty older adults with weak balance voluntarily participated in this study. The study subjects were selected through Berg and Mini-Mental State Examination (MMSE) tests. The subjects who got scores lower than 52 in the Berg test were allowed to participate in the study. On the other hand, those who got scores lower than 23 in the MMSE test were excluded from the study. After subjects’ familiarity with the measurements and taking their informed consents, they walked 12 meters under 2 conditions; normal walking and walking with a cognitive dual-task. Spatial-temporal kinematic parameters were recorded by Vicon cameras. Then, by using the Polygon software, the variables of cadence, walking speed, step length, stride length, duration of step and stride, duration of stance and swing, time of single leg support and double leg support, separation of other leg, touching of other leg to the ground, and time of separation of fingers were calculated in terms of percentages of walking cycle. The obtained data were analyzed using repeated measures ANOVA. 
Results: The results showed that among the examined parameters, the variables of cadence and walking speed during walking with dual-task were reduced significantly compared to normal walking. The duration of the step, stride, time of double support, time of single leg support, the time of standing and swing in walking along with dual-task compared to normal walking showed a significant reduction (P<0.05). Asymmetry index in walking with dual-task compared to normal walking showed a significant increase in parameters of cadence, duration of step and stride; however, the changes in other parameters were not significant. The findings showed that the changes in stepping parameters from one step to the next one in walking with dual-task compared to normal walking had no significant changes. 
Conclusion: The results showed that the duration of double reliance and stance increase when walking with dual task than when normal walking. Therefore, in the elderly with poor balance, doing dual-task with walking could increase the risk of fall. With regard to increase in asymmetry in walking with dual-task, it seems that mutual harmony and symmetry is very sensitive to concurrent cognitive task. This asymmetry in the function of legs is considered a risk factor in falling. Thus, based on the results, walking of the elderly with poor balance needs better cognitive performance. Doing concurrent cognitive tasks could intervene with attention sources and consequently change the walking pattern. Therefore, we recommend that the older people with weak balance and prone to falling should refrain from cognitive dual-task during walking and focus on walking itself.