Age-related changes in muscle fatigue resistance in humans.

Abstract

The goal of this study was to compare the relative contributions from the muscle and the central nervous system to muscle fatigue resistance in aging. Each subject carried out 90 s of sustained maximal voluntary isometric contraction (MVC) of the thumb using the thenar and forearm thumb muscles. Contractile capacity of the thenar muscles was assessed through tetanic stimulation of the median nerve. Interpolated doublets delivered during an MVC represented the overall voluntary activation level while transcranial cortical stimulation with an electromagnetic stimulator was used to assess motor output upstream from the corticomotoneuronal pathway. Nine elderly subjects [four females and five males, 70+/-9 years old (mean+/-SD)] and 10 younger subjects (five females and five males, 30+/-6 years old) were tested. After the fatiguing exercise, the elderly group's MVC declined by 29% as opposed to 47% in the younger group (p<0.01). The elderly group's greater fatigue resistance was accounted for by increased fatigue resistance at the muscle level as well as in the central nervous system. At least some of the decline in the central motor drive was upstream from the corticomotoneuronal pathway. The higher muscle fatigue resistance in the elderly group was attributable to differences in both the peripheral and central nervous systems.