Nerve fiber hypertrophy in posterior tibial nerves of mice in response to voluntary running activity during aging.

Three-month-old male C57BL/10 mice were exercised by voluntary running activity in vertically revolving wheels for two hours each day until 24 months of age. Activity scores were recorded each day and the animals were regularly weighed and inspected for abnormalities. Control animals were similarly treated except that the activity wheels were immobilized. At the end of the exercise period, survival was 84% for the exercise group and 64% for the controls. Light microscopic examination of the posterior tibial nerve of the surviving animals showed a significant fiber hypertrophy in response to the exercise. The number of myelinated fibers in nerves from exercised animals did not differ from those of the controls. On the basis of these data, it is suggested that prolonged exercise does not prevent the loss of peripheral nerve fibers associated with age but rather, may exert an effect on the nervous system by modifying the surviving cells.