Biomechanics and Injury Prevention

For Young Learners

The Principle

Some things about your body you cannot change: how tall you are, the shape of your bones, how old you are.

Other things you can: how strong you are, how you land, how you turn, how tired you let yourself get.

Injury prevention is the idea of finding the things in the second list that matter, and changing them.

At the Knee

When people land badly, their knees tend to fall inwards. That position puts a lot of load on the ligament inside the knee.

You can practise landing with your knees over your toes instead, and with your hips and knees bending to absorb the landing.

Teams that practise this as part of their warm up get fewer knee injuries. That is a real finding, not a guess.

For Patients

The Principle

Prevention works on the part of the mechanics that can be modified. That is a smaller list than people expect and it is not empty.

Strength, movement pattern, fatigue management and load progression are modifiable. Bone shape, joint geometry and past injury are not.

A prevention programme is a set of exercises aimed at the modifiable list, performed often enough to change a habit.

At the Knee

The target is usually the position of the knee under load. A knee that collapses inwards when landing or changing direction is loaded in the direction its ligaments resist least.

Programmes train landing, cutting, balance and strength together, because the position is produced by all four.

They are done as a warm up rather than as extra training, which is what makes them possible to keep doing.

Clinical Relevance

Prevention programmes reduce knee injury rates in several sports when they are actually performed. Adherence is the limiting factor rather than the content.

They matter most to people who have already had an injury, because reinjury is the largest single risk.

Section 8 covers the programmes themselves.

For Medical Students

The Principle

Prevention requires a modifiable variable that is causally related to injury. Both halves are needed: an unmodifiable risk factor cannot be a target and a modifiable association that is not causal will not help when changed.

Neuromuscular training targets the position of the joint at contact, which the mechanics identifies as decisive because the load arrives faster than a correction can be made.

The outcome measure is injury rate rather than a biomechanical variable, which is what separates a prevention trial from a mechanism study.

At the Knee

Dynamic knee valgus during landing and cutting is the usual target. It combines hip adduction and internal rotation, knee abduction and tibial internal rotation. 3.12.7 covers it.

Programmes combine plyometrics, balance, strength and technique feedback. No single component has been shown to carry the effect alone.

Hip strength and trunk control are part of the target, because the knee's position is partly set above it.

What Changes It

Programme effect depends on adherence, on the sport's demands and on the baseline risk of the population.

Fatigue resistance is part of the mechanism, because the protective pattern degrades within a session.

Age affects trainability of movement patterns, and programmes introduced in adolescence are reported to have larger effects.

How It Is Measured

Cluster randomised trials by team are the standard design, with injury rate per exposure hour as the outcome.

Biomechanical outcome measures such as knee abduction moment are used as surrogates and are not the same as an injury outcome.

Screening tests for risk have generally performed poorly at the individual level even where the group association is real, which is a statistical point with practical consequences.

Clinical Relevance

Recommend a prevention programme to athletes in pivoting sports, and to any athlete returning after a knee injury.

Expect the group effect rather than individual prediction, and say so, because screening an individual does not perform as well as the group data suggests.

Address hip and trunk control alongside the knee, since the position being targeted is produced above the joint as well as at it.

MRCS Level

The Principle

State the causal chain being assumed: training changes movement, changed movement changes joint loading, changed loading changes injury rate. Trials test the first and last links together and the middle ones are inferred.

That is a defensible position and worth saying out loud, because it explains why biomechanical surrogates and injury outcomes sometimes disagree.

Prevention and rehabilitation share a mechanism, which is why return to sport programmes look like prevention programmes.

At the Knee

Conventional teaching reports relative risk reductions for knee injury in the range of a third to a half in well conducted programmes with good adherence, with smaller effects in pragmatic implementation.

The effect is larger for anterior cruciate injury specifically than for knee injury in general in several analyses.

Hip abductor and external rotator strength, trunk control and landing technique are the components most often credited, without a clean separation between them.

What Changes It

Adherence is the dominant moderator and it falls over a season without reinforcement.

Coach delivery rather than clinician delivery determines whether a programme survives in a club setting, which is an implementation variable with a mechanical consequence.

Baseline risk changes absolute benefit, so the same relative reduction means different things in different populations.

How It Is Measured

Cluster randomisation by team avoids contamination and complicates analysis. Exposure hours rather than player numbers are the denominator.

Injury definition varies between studies, which affects comparability more than most readers notice.

Surrogate biomechanical endpoints are useful for mechanism and weak for effect size.

Clinical Relevance

Prescribe a programme by name and by frequency rather than advising exercise generally, since adherence is the variable that decides the effect.

Involve the coach where possible, because delivery determines survival of the programme.

Expect a relative risk reduction rather than elimination, and set that expectation with the athlete.

Avoid individual screening as a basis for selection or exclusion, since the tests do not perform at that level.