In this April 8, 2011, file photo, Aliya Mustafina of Russia gets assistance after suffering from an injury at the vault during the women's individual all-around gymnastics final of the Artistic Gymnastics European Championships in Berlin, Germany. Photo: AP Photo/Gero Breloer,File/MCT

The new study compared girls and boys playing the same sport. ######

About 70 percent of these injuries happen when there is no contact with another player at all.

Usually, you feel a pop in the knee and then see swelling, says Randall Schultz, a doctor who works on bones and joints. Sometimes it will hurt - other times, the pain might not be that bad.

###### However, you should see a doctor the next day or after the weekend is over to see what's going on and what needs to be done. In the meantime, put ice on it and use crutches to try to stay off it, Schultz says.

Jump. Turn. Stop. Kick. Pain.

Sports where kids stop suddenly and turn a different direction usually are the cause. ###### Boys also saw problems with football which, unlike the others, is a contact sport. Doctors see injuries arising from all of these sports, along with cheerleading and dance.

The risk goes up for girls once they hit age 12 or 13 and for boys around age 14 or 15. Why? ###### The teen years are a time when kids grow faster, and their bodies can't always keep up. This is especially true of the leg's tibia and femur bones, the two bones on the front of the leg.

For girls, hormones also make the ligaments looser. ###### ]]>