Effects of aging on linear and curvilinear aiming arm movements

This research was designed to test the hypothesis that seniors may have deficits in their movement planning and execution of rapid target oriented arm movements. Twenty senior adults (M = 81.2 years, SD = 1.8) and 20 young adults (M = 25.2 years, SD = 2.5) performed two types of fast aiming arm movements (linear and curvilinear) on a digitizer in a counterbalanced order. Age effects on the variables of movement time, movement jerk, as well as on the profiles of movement displacement, velocity, and acceleration were examined. The outcomes of analysis of variance (ANOVA) with repeated measures indicated that the seniors executed both movement tasks more slowly and had higher movement jerk than the young adults. This suggests that aging is not only associated with slower but less smooth movements. In addition, the examination of movement profiles indicated that the young adults implemented the curvilinear task as one smooth and integrated motion, whereas the seniors executed the task in two segments. One possible reason of this "segmental" execution of curvilinear movement is that seniors may compensate for their deficits in movement planning by adopting a control strategy that reduces movement complexity. The aging effects on rapid aiming arm movements are discussed from the perspectives of motor planning, the "speed-accuracy trade-off," and task complexity.