AGE CHANGES IN RESPONSE SPEED AND NERVE CONDUCTION

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Age is associated with a slowing of movement and loss of strength that affects the accuracy of arm and leg use. At a critical level this can be an important factor leading to functional disability in the elderly. The natural history of how these changes occur and the causes are poorly understood. During the past year, two studies were completed to (1) explore age changes in the relationship between speed of movement time and accuracy, and (2) the contribution of nerve function to age associated loss of strength. A reciprocal tapping test was administered to participants in the Baltimore Longitudinal Study of Aging (BLSA). Movement time increased cross-sectionally and longitudinally with increasing age. After age 40, movement time increases with age was linked to decreased consistency of hitting the targets. Longitudinally, accuracy decreased with increasing age. Fitt's law accurately described the speed and accuracy of hand movements during adult aging, across cohorts and within participants. Age associated muscle strength loss is attributed to decreasing muscle mass. Both strength and mass are dependent on muscle innervation. There is little direct human evidence demonstrating the association between age changes in nerve function and strength. Median and, to a lesser extent, ulnar nerves are the major nerves supplying grip strength. Grip strength and median and ulnar nerve conduction velocities were measured in BLSA participants. Median but not ulnar nerve significantly related to grip strength along with age and forearm circumference. Age and initial grip strength predicted rate of grip strength change with age. Motor nerves, muscle mass and age have significant, independent contributions to age associated levels of strength.