Can You Do Knee Extensions After ACL Surgery?

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If you’ve been told to avoid the knee extension machine after ACL surgery, you’re not alone.

It’s one of the most misunderstood movements in ACL rehab — often banned outright, without context. Patients hear phrases like:

“It’s too much strain on the graft.”
“Just stick to squats for now.”
“That machine’s dangerous after surgery.”

But here’s the reality: most ACL rehab plans include movements that place equal or greater strain on the graft — and we do those without hesitation.

ACL Graft Strain: What the Research Actually Says

Let’s look at the numbers from a well-respected study by Escamilla et al. (2012), published in the Journal of Orthopaedic & Sports Physical Therapy:

Exercise ACL Graft Strain
Lachman Test 3.7%
Squat with +10kg 4.0%
Single Leg Squat 3.2%
Seated Knee Extension (no load) 2.8x ACL strain

Yes — that knee extension movement you’ve been warned about?

It’s actually producing less strain than movements you’re already doing.

So Why Are Knee Extensions Feared?

It’s not the exercise itself — it’s poor timing and poor prescription.

The seated knee extension becomes a problem when introduced too early, especially if:

  • Your knee doesn’t have at least 90° flexion

  • You haven’t rebuilt enough quad control

  • You push aggressively into full extension too soon

This can cause anterior knee pain, irritation, and setbacks — but it’s not the ACL graft that’s at risk. It’s about respecting the stage you’re in and progressing safely.

When Should You Start Knee Extensions After ACL Surgery?

Here’s a safer approach:

  • ✅ Wait until you reach at least 90° flexion

  • ✅ Start with isometric holds between 60–90° of knee bend

  • ✅ Progress gradually into short-range reps

  • ✅ Focus on control, not ego

With this approach, the seated knee extension becomes one of the best ways to target inner range quad strength — something many ACL patients struggle to rebuild.

Why Quad Strength Matters in ACL Rehab

Many ACLers reach 12–16 weeks post-op and still say:

“I can’t feel it in my quads.”
“They still look flat.”
“My knee feels unstable.”

That’s often because isolated quad loading — like seated knee extensions — has been skipped or delayed out of fear.

The result? Slower strength gains, poor symmetry, and limited confidence in your knee.

Get the Full Plan: Safe, Phase-Based ACL Rehab

If you’re going through ACL rehab and feeling lost, underloaded, or confused by conflicting advice…

📘 My Complete ACL Recovery Guide gives you:

✅ Weekly rehab plans from week 1 post-op
✅ Phase-by-phase progressions
✅ Strength testing benchmarks
✅ Guidance on when to introduce exercises like knee extensions — and how

It’s used by both patients and therapists across the world.

Don’t keep guessing what’s safe or effective.
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Final Thoughts

Knee extensions aren’t the enemy — poor timing and a lack of proper guidance are.
When used correctly, they’re one of the most powerful tools for rebuilding quad strength after ACL surgery.

Want a rehab plan that actually makes sense?

👉 Get the Complete ACL Recovery Guide here

Written by:
Tilly Milverton – ACL Rehab Specialist
Instagram: @specialistsportstherapy