July 2010

Fighting fatigue

In the moment: Sports medicine

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Focus shifts to screening, intervention

By Jordana Bieze Foster

As a growing body of research supports the idea that fatigue contributes to sports-related injury, investigators are now working to identify those athletes who may be most vulnerable to the effects of fatigue and interventions that could counteract those effects.

Fatigue was an especially popular topic this summer, at the annual meetings of the National Athletic Trainers Association in July and the American College of Sports Medicine in June.

Opportunities for intervention could start with halftime of a soccer match, according to research from the U.K. suggesting that for most soccer players, halftime may be too passive.

“The pre-match warm-up is something of a ritual. Everyone does it. What we need is to develop a halftime warm-up to consider biomechanical, physiological, and psychological demands of match play,” said Matt Greig, PhD, a senior lecturer in sport & exercise biomechanics at Edge Hill University in Ormskirk, Lancashire, who presented his group’s findings at the ACSM meeting.

Greig and colleagues studied 10 semipro soccer players who completed a 90-minute treadmill protocol designed to simulate a soccer match. The protocol emphasized bursts of acceleration and deceleration, with a change in speed approximately every 4.5 seconds, but also included a passive 15 minute halftime.

As previously reported in the March-April issue of the Journal of Athletic Training, fatigue was associated with significant decreases in eccentric hamstring strength that were not recovered during the halftime period. But the researchers also found that dynamic balance was significantly impaired at the start of the second half in terms of magnitude and pattern of center of gravity displacement. The greatest degree of knee varus displacement during a planar hop test was also seen at the start of halftime, a finding that trended toward significance.

“We go out in the second half in an impaired biomechanical state,” Greig said.

Another study on soccer players suggests that despite the length of most laboratory fatigue protocols, five minutes may be all that practitioners need to determine whether fatigue will increase an athlete’s risk of injury.

In 15 female collegiate soccer players, researchers from Old Dominion University found that neuromuscular changes were more pronounced following a five-minute multidimensional exercise protocol than a 30-minute treadmill run. During a running stop-jump test, both protocols were associated with significant decreases in hip flexion at all time points along with increases in knee internal rotation at initial contact IR at IC, hip abduction at peak force, and knee adduction moment at initial contact.

Because changes were seen after only five minutes, a similar protocol could potentially be used for screening, according to David Quammen, a graduate student in athletic training at the university, who presented his group’s findings at the NATA meeting.

Perhaps not surprisingly, athletes who are recovering from injury appear to be particularly susceptible to the effects of fatigue, according to research from the University of Virginia.

Investigators compared 17 subjects who had undergone anterior cruciate reconstruction with 17 healthy controls following a 20-minute treadmill protocol in which subjects maintained a rate of perceived exertion between 15 and 17. All injured participants were at least two years removed from their surgery.

Following the fatigue protocol, hip abduction strength had significantly decreased from baseline in all subjects. However, decreases in hip extension were significantly more pronounced in the ACLr group. The previously injured subjects also demonstrated poorer performance on the Star Excursion Balance Test, and less gluteus medius activity during the anterior component of the SEBT.

“Clinicians should identify weakness both at rest and post exercise in recreationally active individuals with a history of ACL injury,” said Elizabeth Dalton, MEd, a graduate assistant in athletic training at the university, who presented her group’s findings at the NATA meeting.

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