Age-related changes in muscle fatigue resistance in humans

Objective: The goal of this study was to compare the relative contributions from the muscle and the central nervous system to muscle fatigue resistanc e in aging. Methods: Each subject carried out 90 s of sustained maximal vol untary isometric contraction (MVC) of the thumb using the thenar and forear m thumb muscles. Contractile capacity of the thenar muscles was assessed th rough tetanic stimulation of the median nerve. Interpolated doublets delive red during an MVC represented the overall voluntary activation level while transcranial cortical stimulation with an electromagnetic stimulator was us ed to assess motor output upstream from the corticomotoneuronal pathway. Re sults: Wine 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 M VC declined by 29% as opposed to 47% in the younger group (p<0.01). The eld erly group's greater fatigue resistance was accounted for by increased fati gue 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. Conclusion: The higher muscle fatigue res istance in the elderly group was attributable to differences in both the pe ripheral and central nervous systems.