Functional compensation of human motor units in health and disease

The number of motor units in the human thenar muscles falls gradually over the first 6 decades of life. In healthy humans over 60 years of age and subjects with hemiplegic atrophy, motoneuron disease, diabetic neuropathy and the carpal tunnel syndrome, the loss may be more severe. Provided the motor unit count did not fall below 10–20% of the normal number of motor units, functional compensation could maintain muscle size and strength and mask the severity of motor unit loss.