Montana State University

Balanced muscle development is important to keep knees safe

March 7, 2007 -- By Carol Flaherty MSU News Service


MSU student Sarah Eby jumps forward to illustrate one of the tests in a study of knees just completed by biomechanics researchers at MSU. MSU photo by Jay Thane.   High-Res Available

Subscribe to MSU Newsletters


Bobcat Bulletin is a weekly e-newsletter designed to bring the most recent and relevant news about Montana State University directly to friends and neighbors via email. Visit Bobcat Bulletin.

MSU Today e-mail brings you news and events on campus thrice weekly during the academic year. Visit the MSU Today calendar.

MSU News Service
Tel: (406) 994-4571
msunews@montana.edu
It's 5:30 p.m. and you're in a pick-up basketball game. Do you know where your knee is?

That's a question Mike Hahn might ask you, though he would probably have wires and electrodes attached to your leg when he asked.

Hahn is a Montana State University biomechanics researcher who recently studied awareness of knee position in women athletes. His work also looked at the forces on the knee joint and nerve activity and muscle strength in the thigh in relationship to the menstrual cycle. The goal was to add to information about whether estrogen is a key player in women athlete's increased risk, compared to men, of injuring their anterior cruciate ligament. The ACL helps stabilize the knee, and female athletes suffer four to six times more ACL injuries than male athletes.

The questions are "Why do women have more injuries?" and "Can we strategically prevent these injuries?" When scientists see a gender difference in injury, one of the things they investigate is whether hormones contribute to the different injury rate.

"There are conflicting studies on the role of hormones in women athletes' higher risk of ACL injury," Hahn said. "Some studies of women's college basketball teams on oral contraceptives have shown reduced injuries, but other studies have shown no effect. That leaves a lot of room for speculation."

Initial findings from the MSU study come down on the side of estrogen fluctuations playing little role in the increased incidence of ACL injuries. However, the study had other interesting outcomes, including that the quadriceps muscle group on the front of the thigh acted with greater strength as the lower leg flexed backward than previous research suggested would be the case. The quadriceps worked to balance the efforts of the hamstrings as the knee was flexed.

Hahn and Mary Miles, also a researcher in MSU's Department of Health and Human Development, recruited 10 women athletes who were already taking oral contraceptives. Each participant came to the lab at three different phases of their menstrual cycle. Due to the hormone regimen, the exact phase of the cycle was precisely known.

Then researchers and undergraduate student assistants performed a battery of tests in MSU's Movement Science/Human Performance Lab in the basement of Romney Hall.

For jumping, running and leg extension exercises under weight, the students were wired. Sometimes electromyography equipment recorded the electrical activity in their muscles. At other times, instruments recorded the torque applied to the knee joint as it extended and flexed. In another part of the study, subjects were blindfolded while seated, then asked to first extend, then bend, the lower leg. The goal was to see whether they had accurate sense of their knee position. Testing a person's joint position sense gives researchers an idea of how well the neuromuscular feedback system is working. If it is not providing accurate feedback, the joint can be put into a mechanically risky position without the athlete's knowledge.

In general, the hamstrings on the back of the thigh have been thought to do more work to stabilize the knee as the leg extends than the quadriceps on the front of the thigh do as the knee bends and the heel goes back. The MSU researchers found that, when extending the lower leg, one of the lengthening hamstrings worked at about 34 percent of the activity it used when it was shortening, similar to results from other studies.

However, in the MSU study, the quadriceps were more active than reported in most other studies. When the knee flexed rapidly, the lengthening quadriceps fired at 17-24 percent of the level they used when shortening, three to four times more muscle use than other researchers have found.

"The main implication of this study is for preventing injury in athletes," Hahn said. "The quadriceps insert on the tibia (shin bone) and pull the tibia up and forward. This makes us consider whether, when the quads are stronger than the hamstrings, they may overpower the system during a high intensity sport and pull the tibia forward to the point of tearing the ACL."

"The take-home message is that we need to have balanced development of the muscles for the knee to function well in high intensity activities," he said.

To see a short story on how to develop balanced thigh muscles, go to http://www.montana.edu/cpa/news/nwview.php?article=4605

Contact: Michael Hahn (406) 994-7154 or mhahn@montana.edu