Ageing movement control

Normal aging movement control in humans is about the changes in the muscles, motor neurons, nerves, sensory functions, gait, fatigue, visual and manual responses, in men and women as they get older but who do not have neurological, muscular (atrophy, dystrophy...) or neuromuscular disorder. With aging, neuromuscular movements are impaired, though with training or practice, some aspects may be prevented.

For voluntary force production, action potentials occur in the cortex. They propagate in the spinal cord, the motor neurons and the set of muscle fibers they innervate. This results in a twitch which properties are driven by two mechanisms: motor unit recruitment and rate coding. Both mechanisms are affected with aging. For instance, the number of motor units may decrease, the size of the motor units, i.e. the number of muscle fibers they innervate may increase, the frequency at which the action potentials are triggered may be reduced. Consequently, force production is generally impaired in old adults.

Aging is associated with decreases in muscle mass and strength. These decreases may be partially due to losses of alpha motor neurons. By the age of 70, these losses occur in both proximal and distal muscles. In biceps brachii and brachialis, old adults show decreased strength (by 1/3) correlated with a reduction in the number of motor units (by 1/2). Old adults show evidence that remaining motor units may become larger as motor units innervate collateral muscle fibers.

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