In tonight's Medical Watch -- the difference between boys and girls... specifically how we use our muscles for exercise. Knowing the difference can help prevent injury.

Dr. Cynthia LaBella, Medical Director of the Institute for Sports Medicine at Children's Memorial Hospital: "Girls rely on the skeletal system, their ligaments and their bones, to stop their knee motion."

In contrast, boys use their muscles to soften the landing and absorb the impact, a lesson Sheila Morrissey learned the hard way after spraining her ankle.

Sheila Morrissey, St. Ignatious volleyball player: "Before I was just kind of like falling down, you know, just like landing. But now I'm more agile I guess, I come down in like a peaceful, more relaxed way."

The newfound strength, control and balance is thanks to the Knee Injury Prevention Program or KIPP, the brainchild of sports medicine experts at Children's Memorial Hospital.

Michael Huxford, Sports Medicine Coordinator of the Institute for Sports Medicine at Children's Memorial Hospital: "We decided to go after female athletes between the ages of 13 and 18. Why? Because they typically have the majority of ACL tears in athletics, compared to boys playing the same sports."

The ACL injuries are due to three main differences: the ligament dominance for girls versus muscle strength. Girls have stronger quadricep muscles, but not hamstrings.

Dr. LaBella: "Girls contracting the quad much more than the hamstring, so it's an unbalanced force on the knee."

And girls have a dominant leg.

Dr. LaBella: "Girls are much more likely to have one leg slightly stronger than the other, and use that leg more often. Boys are much more likely to have even strength distributed between the two legs."

Knowing the deficits for girls gives experts a leg up on fixing them. Namely strengthening and evening the body. Coaches learn specific exercises in the KIPP program.

Michael Huxford: "I wanna point out exercises 1-10 on practice day A. Practice day B and on the back with game day."

Courtney Sommerville's volleyball team started KIPP this year, and after 5 years playing, she says this year the sky is the limit.

Courtney Sommerville, St. Ignatious volleyball player: "Balance has become better I've noticed, and increase in vertical, which is really important with volleyball."

Dr. LaBella: "The girls that were doing these exercises were much less likely to be injured, knee sprains, ankle sprains, ACL injuries compared to the group that didn't do these exercises. If I can be out here teaching this program instead of in the clinic treating the injuries then I'm still practicing medicine and in my view, I'm doing a better job than waiting for the injury to happen and then treating. I'd rather be on the other end and prevent it."

There is a brochure with all of the exercises and the Chicago Fire Soccer Club is providing funds for coaches to take the KIPP training program.

Two more free training sessions will be offered this summer at Toyota Park, Home of the Chicago Fire, in Bridgeview, IL Tuesday, July 27 and Wednesday, August 11.

For more information, please visit, or call (773) 327-1201 to register.