Motor Performance

The slowing of movement in older adults can be seen in everyday tasks such as reaching and grasping, point-to-point movements (discrete goal-directed aiming movements with a defined beginning and end), and continuous movements (cyclical movements, such as circles, with no defined beginning and end). Movement time (MT) provides an assessment of the speed of task execution. Movement time is defined as the time from the initiation of a particular movement to the termination of the movement. Movement times in older adults are substantially slower than young adults, ranging from 20 to 70 percent slower, depending on the complexity of the task. A variety of tasks have been assessed, including movements of the finger, hand, arm, and trunk.

Fitts' Law (Fitts) describes increases in MT as a function of task complexity (see Figure 1). Movement accuracy is manipulated by increasing the distance traveled to a target or increasing the size of the target, and tasks can be analyzed through an Index of Difficulty (ID). For both young and older adults, MT increases linearly as ID increases. However, older adults are slower than young adults at the lowest levels of difficulty, and MT increases at a greater rate as difficulty increases.

Movement-time measures are important in assessing movement slowing, however they do not provide explicit insight on the underlying mechanisms of slowing or on specific changes in control. Research has therefore focused on movement decomposition in an effort to identify particular movement characteristics that contribute to movement slowing, allowing researchers to assess fundamental changes associated with movement slowing in older adults.