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Normal aging movement control in humans is about the changes on 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. ==Force production== 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 2 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.〔Neuromechanics of human movement, chapter 6 Single-joint system function; Roger M. Enoka.〕 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. In first dorsal interosseus, almost all motor units are recruited at moderate rate coding, leading to 30-40% of maximal voluntary contraction (MVC). Motor unit discharge rates measured at 50% MVC are not significantly different in the young subjects from those observed in the old adults. However, for the maximal effort contractions, there is an appreciable difference in discharge rates between the two age groups. Discharge rates obtained at 100% of MVC are 64% smaller in the old adults than in the young subjects: 31.1 ± 11.8 impulses/s in the old subjects, 50.9 ± 19.5 impulses/s in the young subjects. Isometric strength and physical cross-sectional area of the elbow flexors and elbow extensors are reduced in old compared with young men. The normalized force (maximal voluntary force to the size of the muscle producing the force) of the elbow extensors is the same for old and young people. The normalized force for the elbow flexors is reduced in the old men compared to the young men. The lower normalized force of the elbow flexors may be due to an increase in agonist-antagonist muscles coactivation. Compared to the young group, the old group has lower dorsiflexors isometric torque at all angles, has lower knee extensors isometric torque at angles >90°. The impairment in force production is muscle specific. During dynamic exercise, the old group requires more time to reach a target velocity and is less able to attain high velocities. The slowing of voluntary contractile speed with age seems to play a role in the loss of dynamic torque. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aging movement control」の詳細全文を読む スポンサード リンク
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