Kinematics of arm movements in elderly humans.

Changes in the kinematics of arm movements with age were studied. "Young" (aged 21-23) and "elderly" (aged 68-95) subjects performed a visually guided, step tracking task. Each subject performed movements of eight different amplitudes (10-80 deg) at two volitionally determined speeds ("own speed," "fast and accurate"). Movement durations and maximum velocities were similar for both groups and increased with movement amplitude under all conditions. The young subjects made movements in which approximately the same length of time was spent in accelerating as in decelerating the movement. In contrast, movements by the elderly subjects were temporally asymmetrical, the deceleration phase being longer than the acceleration phase. The ratio of maximum to average velocities (Vm/Vav) was markedly different between the young and elderly subjects, particularly in the smaller amplitude movements (less than 40 deg). Values of this parameter ranged from 1.5 to 6 in the elderly subjects. Movements made by the elderly subjects were more variable than those of the young subjects, particularly so at smaller amplitudes. Variability was most apparent in the deceleratory phase of movement where the elderly subjects often showed hypermetria. Some elderly subjects also showed movement decomposition, the movements being made as a series of discrete submovements. Thus, the elderly subjects displayed some of the characteristics classically described as arising from cerebellar dysfunction.