Motor Performance

To produce movement, force must be generated by the muscles driving the body segment involved in a movement. These forces must be scaled to increase velocity; but, perhaps more importantly, the timing of muscle activation must synchronize with multiple other muscles and subsystems of the motor-control system. Research has shown that older adults have reductions in force production and regulation across a range of tasks, which limits their ability to make fast, accurate movements. Properties that may contribute to such changes are loss in muscle mass and a reorganization of motor units. However, it has further been shown in tasks in which accuracy constraints are relaxed that older adults are able to produce similar forces as young controls produce. This suggests that while muscle loss and motor unit reorganization may lead to decreases in force production, it is most likely not the limiting factor in tasks such as reaching and grasping and point-to-point movements, in which force output is submaximal. Therefore, there must be other mechanisms that contribute to force-control deficits in the presence of accuracy constraints in older adults. A possibility is that the fine ramping of force production is compromised in the reorganization of motor units, which are essential in fine motor tasks such as reaching and grasping and point-to-point movements.

In precision grip tasks, older adults produce excessive force in an effort to keep the grasped object from slipping. Again, older adults, while able to produce sufficient and even excessive force, are unable to effectively modulate and time force output. This is amplified when grip surfaces are slippery—in such instances older adults substantially increase grip forces beyond the necessary level to keep the object from falling. This suggests that it is peripheral feedback-mechanism decrements such as proprioception or tactile feedback, and/or processing capacity, that are compromised with advanced age and limit performance of older adults in these fine motor tasks.