What Causes ACL Injuries and Can They Be Prevented?
- Murray Leyland
- Aug 12
- 3 min read
Updated: Aug 15
Short answer: largely, yes. ACL injuries fall into two types: contact tears from a tackle or collision, which can't be prevented, and non-contact tears from ordinary landing and change-of-direction movements, which make up most cases. That second group responds to training, with the right strength and warm-up program cutting injury rates by up to 60%.
Most ACL injuries don't happen in a tackle. They're often the most innocuous thing you'll see on a football field — a player is running, boom, they're down, and nobody touched them. That moment confuses players, parents, and coaches every weekend. So let's unpack what actually causes ACL injuries, who's most at risk, and what you can actually do about it.
Are ACL injuries just bad luck?
That's the misconception: ACLs just happen, they're bad luck, and there's nothing you can do about them.
The research says otherwise. Effective strengthening and warm-up programs can reduce ACL injury rates by up to 60%. You don't get a number like that from injuries that are purely random. It tells us there's something trainable underneath most of them.
To understand that, you need to know there are two very different kinds of ACL injury.
How do most ACL injuries actually happen?
Contact injuries are the ones everyone pictures. You're in a tackle, someone crashes into the knee, and it gives. These are unavoidable. They're simply part of the deal when you play contact sport, and no program prevents them.
Non-contact injuries are the bigger group, and they follow three classic patterns:
Watch enough football and you'll recognise all three instantly. No contact, no tackle. Just a movement the player has done thousands of times before, going wrong this one time.
Who is most at risk of an ACL injury?
The risk factors are well established:
If you or your kid ticks a few of those boxes and plays a pivoting sport, prevention work isn't optional extra credit. It's the smartest training investment you can make.
Why does the knee fail on that one movement?
Here's the honest part. Despite enormous research investment, we still can't identify the exact neuromuscular event that makes a knee fail at that precise moment.
The player who tears their ACL cutting left in the 15th minute has performed that exact zig and zag hundreds, probably thousands of times before without a problem.
Why that rep? Why not last week, or the other thirty times they did it at training? To truly answer it you'd need to scan a thousand footballers' knees every day for five years, and nobody's running that study.
But we do have one very revealing clue: when ACLs happen during games.
Why do warm-ups prevent ACL injuries?
ACL injuries cluster in the first 20 minutes after each half, not at the fatigued end of halves. So it's not primarily a tiredness problem. It's a coordination and accuracy problem. Players get hurt when the connection between brain and knee isn't dialled in yet.
That's the mechanism behind that up-to-60% reduction. Strength work builds the capacity. The warm-up switches it on.
What should I do next?
Whether you've unfortunately injured your knee and want guidance on your ACL rehab, or you want a prevention program for yourself, your kid, or your team, this is what we do. ACL management and prevention is a field we're expert in.
During my years as Head Physiotherapist for the Central Coast Mariners, keeping knees on the park was a core part of the job, and it's work we continue every week at Valley Physiotherapy across Thornton, Kurri Kurri, and Maitland.
Book an appointment and we'll either map out your recovery or build you the exercises designed to keep you on the park. And if you've got questions, reply to this email and I'll happily give you a hand.
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