The mechanism
The typical non-contact ACL injury happens in a fraction of a second: landing from a jump or planting to change direction, with the knee relatively straight, the trunk leaning, and the knee collapsing inwards over the foot.
That position places high load on the ligament at a moment when the muscles are not positioned to protect it. Recognising the position is important, because it is the same position that can be trained out.
Why risk rises at puberty
Before puberty, ACL injury rates are similar between boys and girls. The divergence appears with maturation, which points to modifiable neuromuscular factors rather than fixed biology.
- Increased body mass and limb length raise the forces at landing.
- Strength gains do not automatically keep pace with those forces in girls.
- Growth changes coordination temporarily, reducing control.
- Sport demands intensify at exactly the same age.
The modifiable risk factors
- Dynamic knee valgus on landing and cutting.
- Low hamstring strength relative to quadriceps.
- Poor single-leg control and hip strength.
- Stiff, upright landing patterns with limited hip and knee flexion.
- Fatigue and congested fixture schedules.
- Low energy availability, which impairs tissue quality and recovery.
What prevention programmes contain
The successful programmes are strikingly similar: a 15–20 minute structured warm-up performed two to three times a week, containing running mechanics, strength, plyometrics, balance and specific landing and cutting technique work with coaching feedback.
They work when they are done consistently, and their effect disappears when they are dropped mid-season. Compliance is the single biggest determinant of benefit.
Coaching the landing
- Land softly - hips back, knees bent, quiet feet.
- Knees track over the middle of the foot, never inside it.
- Absorb through the hips rather than stopping the movement at the knee.
- Practise stopping in three steps, not one, when decelerating from a sprint.
- Train it fresh and fatigued, injuries happen late in matches.
The practical message for parents
This is one of the few areas of youth sport where a specific, well-evidenced intervention exists and is rarely used. A 15-minute warm-up, done properly, three times a week, is the single highest-value action available for an adolescent female athlete in a cutting or jumping sport.
If your child's club does not run one, the same programme can be done at home before training or matches.