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Friday, October 22, 2021

Preventing the dreaded knee injury

A recent UC Davis Human Performance Laboratory study found that landing on the toes after a forward jump cuts forces on the anterior cruciate ligament (ACL) in half, potentially preventing the ACL from snapping.

The study, led by neurobiology, physiology and behavior professor David Hawkins, outfitted 14 female high school and college basketball players with sensors and reflectors and asked them to perform a jump-stop movement on camera. Typically, when a player leaps forward to plant both feet (a jump-stop), she will land on her heels, which transfers most of the force to her knees.

The researchers then asked the subjects to do a second jump-stop, this time landing on their toes. All 14 subjects reduced shear (back-and-forth) forces between the thighbone and shinbone by an average of 56 percent.

Keith Baar, assistant professor of neurology, physiology, and behavior, described safe jump-stop form as nearly identical to proper squat form.

“When you’re doing squats, the feet need to be ahead of the knees. That way, the force is transferred off the knees, onto the feet and muscles,” Baar said.

Protecting the knee is important even in squats, and the stakes get higher as the forces on the knee increase.

The ACL is one of the two ligaments that run through the core of the knee in an X shape, linking the thighbone and shinbone together. Ligaments are the connective tissues that hold bones together, like thick rubber bands. Unlike the muscles, ligaments can’t contract to create movement: they prevent movements instead, stabilizing joints and keeping the bones from sliding out of place.

ACL tears happen when the shinbone (tibia) is jarred out of place, whether by an impact or by the forces created by dodging, stopping suddenly or landing from a jump. Since 100 percent of the study’s subjects reduced these shear forces by landing on their toes, this modification seems like an obvious way to prevent ACL tears.

But the problem is that athletes in high school and college, who are most likely to be injured, have already established ligament-damaging movements into their muscle-memory, said UC Davis women’s basketball coach Sandy Simpson.

“The problem is incorporating the findings into the athletes’ habits,” said Simpson. “When they get to our level, the movements are ingrained. At the younger levels, it would help to have that kind of training.”

Early preventative training is the focus of Gretchen Casazza’s latest research. Casazza, the research director for UC Davis Sports Medicine, is developing an electronic training device: a portable sensor that attaches to the knees or ankles to monitor the player’s positioning. The sensor will have a feedback feature, like a vibration, in response to an incorrect position.

Casazza has been working with her daughter’s soccer team since the girls were eight, and now they’re 14 – the age at which ligament-saving training drills become crucial. Her invention, combined with Hawkins study, provides a good theoretical basis for developing such drills for young athletes.

“Just knowing the biomechanics and what goes wrong isn’t enough,” said Casazza. “You need to know how to develop a strength program that can prevent these injuries.”

EMILY GOYINS can be reached at science@theaggie.org.

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