NEW YORK (Reuters Health) - While a stiff leg may help you run faster and jump higher, it may also make you more prone to sitting on the sideline, hints a new study of Australian Rules Football players.
Researchers found significantly more preseason leg and hamstring stiffness among players who would later sustain a strain, compared to those who maintained healthy hamstrings throughout their practices and matches.
Australian Rules Football, a variant of football, is a high-intensity, intermittent running game, combining skills such as kicking, hand passing, and jumping. It is played on a large oval-shaped grass field.
“Hamstring injuries occur regularly in Australian Rules Football,” lead researcher Mark Watsford of the University of Technology in Sidney, Australia, told Reuters Health in an email.
Although some risk factors have been identified, such as age and prior injury, Watsford and colleagues wanted to see if they could identify a modifiable risk factor that was associated with such an injury. Such a finding could point to a testing and training program for injury prevention.
At any given time, 15 percent of each Australian Rules Football club’s roster is on the sidelines with an injury, the most common ailment being a strained hamstring. And one out of every four players with this injury is likely to suffer the muscle pull again.
To find out if the potentially preventable factor of stiffness could explain this high rate, Watsford and his colleagues followed 136 players from four clubs over the course of the 2006 season.
Each athlete underwent a series of tests to measure leg and hamstring stiffness a month prior to the first match. Subsequent hamstring injuries were defined as pain on the back of the thigh that was tender to the touch and kept a player out of at least one match.
About one of every ten players suffered a non-contact hamstring injury during the season, the researchers report in The American Journal of Sports Medicine. These 14 athletes had, on average, 11 percent higher hamstring and 5 percent higher leg stiffness during the preseason compared to the non-injured athletes.
But when the researchers looked more closely at the differences in stiffness between the left and right legs of injured players, a paradoxical finding emerged: the injured limb actually displayed less stiffness than the opposite limb.
Because stiffness is linked to strength, explained Watsford, the weaker leg may not have been able to handle higher levels of stress, resulting in a muscle strain.
“High performance athletes require dynamically stiff lower extremities to maximize their efficiency and speed,” Robert Butler of Duke University in North Carolina, who was not involved in the study, noted in an email to Reuters Health. “However, the other side of this is that excessive stiffness can place too much strain on the tissue and lead to injury.”
Watsford and colleagues note that the small number of injuries sustained and the extended time between preseason assessment and the injury may restrict the applicability of their results.
Nevertheless, the limited findings can be generalized across other team-based sports, such as soccer and rugby, which have similar rates of hamstring injuries.
Since stiffness is a modifiable factor associated with hamstring injury, “monitoring muscle stiffness levels certainly appears to be an important component of tracking athlete well-being,” said Watsford.
Strength training or plyometrics -- exercises designed to produce fast, powerful movements -- can then be used to increase stiffness, he added, while flexibility training can reduce it.
The American Journal of Sports Medicine, online July 1, 2010.
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