Fatigability is increased with age during velocity-dependent contractions of the dorsiflexors

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.

The fatigue protocol involved 25 maximal (as fast as possible) contractions at a load of 20% maximum isometric strength through a 25 degrees range of motion. Electromyographic signals of the tibialis anterior and soleus muscles were recorded to assess agonist activation and antagonist coactivation, respectively.

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.

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.