Last reviewed: September 29, 2026

The reason is not fully known. But the risk can often be lowered with a warm-up program.

The ACL is a ligament in the middle of the knee. Most tears happen without contact, when a player lands from a jump or cuts to change direction.

In a review of high school–age athletes, girls tore the ACL about one and a half times as often as boys overall. In basketball, the girls’ risk was about four times the boys’. Among girls, soccer had the highest rate. Tears were far more common in games than in practice.

Why this happens is not settled. Studies have linked several things to the difference. These include the shape of the knee, a narrower space where the ACL sits, landing with straighter knees, and muscle strength that does not keep up with growth after puberty. Studies of hormones and the menstrual cycle are inconclusive. Birth control pills have not been shown to lower the risk. None of these has been proven to cause the tears. Landing tests used to screen players have not been able to predict who will tear the ACL.

Prevention has been studied more. Warm-up programs that combine jumping and landing practice with strength, balance and agility exercises lower the rate of ACL tears. In a review of studies in young female athletes, the programs cut ACL tears about in half. The benefit was greater in middle and high school players than in older athletes. Programs that worked were usually done two to three times a week, for about 20 minutes, through the whole season. The benefit depends on teams actually doing them. The evidence in boys is more limited.

According to the American Academy of Orthopaedic Surgeons, these programs can be used to lower ACL risk in high-risk sports. Knee braces are not a preferred way to prevent ACL tears.

In general:

  • Ask the coach whether the team uses an injury prevention warm-up.
  • Programs seem to work best when started young and done all season long.

Drafted with AI assistance from published sources, reviewed and edited by Babak Sheikh, MD.

Sources:

This is general information about what published research shows. It is not medical advice and it is not about your situation. Reading it does not create a doctor-patient relationship with me. I am a retired orthopedic surgeon and I do not see patients. Talk with your own doctor before changing anything about your care. If something feels suddenly or seriously wrong, get medical care promptly rather than waiting.

This page is provided as is. I make no guarantee that it is accurate, complete or current, and medical evidence changes. Use of it is at your own risk.

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