Motor Performance

Older adults also exhibit heightened movement variability in kinematic and endpoint measures. Variability has been documented in such measures as movement trajectory, peak velocity, movement duration, ratio of acceleration and deceleration phases, and force control. Compensation for movement variability may result in behavioral outputs that are a consequence of, rather than a mechanism of, movement variability and/or slowing. Seidler-Dobrin et al. (1998) found that older adults coactivate the agonist and antagonist muscles during movement, leading to altered muscle activation patterns, which consequently contributes to increased variability. Older adults also exhibited longer deceleration phases of movements. Coordination of multiple joint segments involves very complex control. Studies of handwriting, bimanual coordination, and multijoint coordination have found that older adults lose fine motor coordination and have increased normalized jerk, which is a measure of movement smoothness. This is manifested in decreased peak acceleration, deformations of desired movements at lower speeds, and bimanual coordination declines at lower speeds.