Study Reveals New Insight About Muscle Fatigue |  
|
Dec. 6, 2006 -- A University of Wyoming professor is the lead author on a new study that links a muscle's resistance to fatigue to the metabolic pathway responsible for force production.
Matthew Bundle, assistant professor in the College of Health Sciences Department of Kinesiology and Health, wrote the report with investigators from Rice and Harvard universities while he was a research fellow at Rice in Houston, Texas. The study, published in the November issue of the "American Journal of Physiology," suggests an alternative training approach for athletes who compete in short-duration events.
Researchers asked six males to perform 30 all-out sprints on a stationary bicycle at different levels of pedal force. In a unique twist, the subjects cycled with both legs, and also with only one leg while resting their unused legs on an adjacent stool. The researchers knew that the relative reliance on the active metabolic pathways providing the energy necessary for contraction would differ during the one- and two-legged conditions.
During exercise, muscles break down and resynthesize the chemical ATP (adenosine triphosphate), which serves as the energy source for muscle contractions. Bundle explains that during less vigorous muscular activity, all of the ATP needed for muscular contraction can be provided via aerobic pathways that utilize oxygen delivered through the bloodstream, allowing moderate levels of exercise without fatigue for prolonged periods. During more vigorous exercise, such as sprinting or lifting heavy weights, the aerobic provision of ATP is supplemented by anaerobic pathways that do not rely on oxygen delivery. While the anaerobic pathways provide ATP very rapidly, their ability to fuel force production is short-lived.
The researchers knew that the rates of oxygen delivery, aerobic metabolism and the amount of "aerobic" muscle force generated would be greater during the one-legged condition because the heart and circulation can provide more blood and oxygen when only one limb is active. Bundle says the researchers found a greater fraction of the total muscle force was provided from aerobic pathways during the one- versus two-legged sprint trials.
To document the onset of fatigue during the sprints, the scientists measured the electrical activity produced by the contributing muscle cells. During the one- and two-legged sprints performed at pedal forces greater than those that could be supported by the aerobic pathways, the researchers observed progressive increases in electrical activity in the thigh muscles, indicating that new muscle fibers were being used throughout each trial to provide the muscle force necessary to maintain constant pedal force. And due to lesser pedal forces during two-legged cycling, the onset of compensatory muscle recruitment occurred at lower thresholds.
Bundle says the study conclusively suggests that relying on the anaerobic pathways for chemical energy causes fatigue.
"The threshold at which you start to use anaerobic energy is when fatigue begins to set in," Bundle says. "The role of the aerobic system in short-term performance is under-appreciated." He notes that athletes focused on short-duration events may benefit from endurance training.
The study's co-authors were Peter Weyand, assistant professor of kinesiology at Rice, and Carrie Ernst, Matthew Bellizzi and Seth Wright, all at Harvard. The U.S. Army Medical and Materiel Command, the National Institutes of Health and the National Research Council funded the research.
Posted on Wednesday, December 06, 2006
|
