Fatigue during multijoint exercise: biomechanical central, peripheral, and age-related aspects
T h e U n i v e r s i t y o f U t a h G r a d u a t e S c h o o l STATEMENT OF DISSERTATION APPROVAL The dissertation of Steven Joseph Elmer has been approved by the following supervisory committee members: ABSTRACT Exercise-induced fatigue is often evaluated during isometric tasks that involve a small muscle mass. The purpose of this dissertation was to utilize dynamic exercise including a large muscle mass to provide additional insight into biomechanical, central, peripheral, and age-related
... l, and age-related aspects of fatigue. Specifically, I used high-intensity submaximal cycling (SUB cyc time trial) to induce fatigue and quantify associated effects via pre-to postexercise changes in maximum cycling (MAX cyc ) power including jointspecific powers and power-rpm relationships. In the first study, I evaluated the effects of fatigue on changes in SUB cyc and MAX cyc joint-specific powers. Joint-specific powers were maintained during SUB cyc but were substantially compromised during subsequent MAX cyc . Changes in MAX cyc power manifested with differential power loss at each joint with ankle plantar flexion (-43%) and knee flexion (-52%) exhibiting relatively greater fatigue than knee extension (-124%) and hip extension (-28 ± 6%). These data demonstrate that exercise-induced fatigue can have distinct consequences for MAX cyc but not for SUB cyc joint-specific power production. For the second study, I induced fatigue in one leg and examined whether fatigue "crossed-over" to the rested contralateral leg. Despite considerable power loss in the fatigued leg (-22%), MAX cyc power was maintained in the rested leg. Thus, a cross-over of fatigue was either not present or not large enough to impair MAXcyc power in the rested leg. These results along with the lack of changes in maximum isometric handgrip force indicate that impairments in voluntary neuromuscular function were specific to those muscles involved in the fatiguing task. In my third study, I evaluated the effects of aging on the development of functional consequences of fatigue. Even with > 30 yr difference in age (26 ± 4 vs. 57 ± 5 yr), masters cyclists exhibited nearly identical levels of fatigue compared to young in the fatigued leg (-21 vs. -22%). Similar to young, masters cyclists were able to overcome fatigue in this leg and produce the same baseline MAX cyc with the rested leg. These results likely represent a best case scenario for healthy active aging. Collectively, these results provide insight into changes in dynamic neuromuscular function associated with high-intensity endurance exercise.