Ing that chronic exercise may preserve MU function with advancing age. This has not previously been examined in humans. Purpose: Thus, the purpose of this study was to estimate the number of functioning MU in the tibialis anterior of masters runners (∼65 yr) and to compare the values with recreationally active young (∼25 yr) and healthy age-matched controls (∼65 yr). Methods: Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular EMG signals during dorsiflexion at 25% of maximum voluntary isometric contraction. Results: The estimated number of MU did not differ between masters runners and young, but MU number estimates were lower in the old (91 ± 22 MU) compared with the masters runners (140 ± 53 MU) and young (150 ± 43 MU). Conclusion: These results demonstrate that lifelong high-intensity physical activity could potentially mitigate the loss of MU associated with aging well into the seventh decade of life....

-matched recreationally active controls. This suggested that long-term exposure to high levels of physical activity may limit the loss of MU numbers with adult aging. However, it is unknown if this finding is the result of long-term activation of the specifically exercised motoneuron pool (i.e., tibialis anterior) or an overall systemic neuroprotective effect of high levels of physical activity. Purpose The purpose was to estimate the number of functioning MUs (MUNEs) in the biceps brachii (an upper body muscle not directly loaded by running) of nine young (27 ± 5 yr) and nine old (70 ± 5 yr) men and nine lifelong competitive master runners (67 ± 4 yr). Methods Decomposition-enhanced spike-triggered averaging was used to measure surface and intramuscular EMG signals during elbow flexion at 10% of maximum voluntary isometric contraction. Results Derived MUNEs were lower in the biceps brachii of runners (185 ± 69 MUs) and old men (133 ± 69 MUs) than the young (354 ± 113 MUs), but the old and master runners were similar. Conclusions Although there were no significant differences in MUNE between both older groups in the biceps brachii muscle, with the number of subjects tested here, we cannot eliminate the possibility of some whole-body neuroprotective effect. However, when compared with the remote biceps muscle, a greater influence on age-related spinal motoneuron survival was found in a chronically activated MN pool specific to the exercised muscle....

Background. Muscle power is more relevant to the activities of daily living than is isometric strength. However, dynamic contractions have received little attention as they relate to the effect of age on muscle fatigue, particularly in very old persons. Thus, the purpose of this study was to investigate fatigue of the dorsiflexors during a velocity-dependent (isotonic) power task in 12 young (26 years), 12 old (64 years), and 12 very old (84 years) men. Methods. The fatigue protocol involved 25 maximal (as fast as possible) contractions at a load of 20% maximum isometric strength through a 25° range of motion. Electromyographic signals of the tibialis anterior and soleus muscles were recorded to assess agonist activation and antagonist coactivation, respectively. Results. Fatigability increased progressively with age as muscle power decreased by 13% in young men, 19% in old men, and 24% in very old men. In contrast, agonist activation and antagonist coactivation were unaffected by age. During the fatigue protocol, agonist activity decreased by 3%, 5%, and 4%, whereas antagonist activity increased by 11%, 13%, and 13% in young, old, and very old men, respectively. Conclusion. These results demonstrate that older adults are more fatigable than young adults during a velocity-dependent power task. This finding is in contrast to the majority of fatigue data previously reported from less functionally relevant isometric or isokinetic tasks.