Believe it or not, catching a ball can actually make you more likely to suffer a knee injury. Injuries to the anterior cruciate ligament (ACL) of the knee are more common in sports like basketball, which involve sudden stops and ball handling. Researchers in Australia tested why that may happen.
They tested seven male and 11 female recreational athletes with an average age of about 23. The subjects ran three steps and then jumped onto a force platform, where they landed on one leg. Sometimes, without advance warning, they had to catch a ball as they landed.
The subjects were filmed and their muscle activity measured as they did the jumping tests. Researchers found that catching a ball didn’t change the movements or angle of the legs, hips, or body as the subjects landed on the platform. However, catching a ball made major changes in the timing of muscle contractions. Something about catching a ball made the quadriceps contract earlier and the hamstring contract later than during the other landings.
Normally, the hamstring muscle keeps the tibia bone in the lower leg centered. This keeps it from sliding forward under the femur bone of the thigh. If the quadriceps muscle on the front of the thigh tightens without the opposing action of the hamstrings, the tibia gets pulled forward. This causes the ACL to become taut to the point where it can stretch out. It may even tear.
Proper muscle coordination when landing on one leg helps protect the ACL and the rest of the knee from heavy force. This study shows that catching a ball can alter muscle coordination between the quadriceps and hamstring muscles, making the ACL more vulnerable to injury. But why this happens is still a mystery that demands more research.