Doctors say they are seeing more torn ACL cases in elementary schools, from children playing tackle football to doing gymnastics, and the numbers are so large that pediatric orthopedic surgeons like Dr. Daniel Green at New York’s Hospital for Special Surgery are calling it an epidemic.

“We recently looked at the database in New York and found a five- to six-fold increase over the last 20 years of ACL surgeries in children,” Green said.

The ACL, the main stabilizing ligament of the knee, is not strong enough to take the strain of repeated movements by itself; the whole knee must be strong.

Children who play the same sport repeatedly – doing just a few moves over and over again – are at risk and girls even more so. They are six times more likely to tear their ACL than boys, according to the PEP Program: Prevent Injury and Enhance Performance, which has developed exercise routines to lower the risk.

New data says there’s a simple solution that reduces the risks: warm-up exercises to strengthen the muscles around the knee, no matter what sport.

The exercises take about 15 to 20 minutes and can be done before practice, according to the PEP program, which was developed by the Santa Monica Sports Medicine Research Foundation, and the FIFA 11+ warm-up program.

Such warm-ups, according to one study, reduce childhood ACL tears by 74 percent. Now the goal is persuading coaches across the United States to adopt them.