02/06/2026
Stop avoiding the knee extension machine ❌
There’s one piece of gym equipment that ACL rehab patients avoid more than any other.
The knee extension machine.
And honestly? The fear is outdated.
Here’s what the research actually shows:
→ Isometric knee extensions at 90° and 60°: essentially ZERO ACL strain
→ Walking: ~13% ACL strain
→ Gravity-only knee extensions: ~2.5% — far less than walking
Squats, stair climbing, and Lachman testing can strain the ACL just as much — or more — than some open-chain movements. (Escamilla et al., 2012)
So when can you start?
For an isolated ACLR, once your knee comfortably reaches around 60° of flexion. Most clinicians wait until 90° feels comfortable, then begin isometrics at 90° and 60° — a biomechanically safe mid-range.
The early isometric protocol:
- 3 sets × 6 reps
- 5-second holds
- 2–3 times per day
- Pain ≤ 2/10
- Start at 90°, then 60°
The first set often feels rubbish. By the third, things usually fire better. That’s AMI (arthrogenic muscle inhibition) being cut through early.
When it’s time to load:
Build into the 45–90° range, targeting around 70% 1RM. Use 12–15 reps as your practical guide. If you’re hitting 20+ reps easily, go heavier. Under 8? Too heavy.
The Forelli 2023 study put this to the test with 103 recreational athletes after hamstring autograft ACLR — early open-chain loading from 4 weeks produced quad LSI of 91% vs 62% at 6 months. No significant increase in anterior tibial translation.
The evidence has moved. The machine hasn’t changed. Time for our protocols to catch up.
One more tip: Pre-exercise cryotherapy can reduce pain and inhibition. Pre-cool. Train. Post-cool. Better contraction → better session → better consistency.
Don’t fear the knee extension machine.
Shout out to .physio for always bringing information like above & much more easier to digest / understand resources for all physios.
Thanks Mic 🙌
coming in clutch 🔥🏆🦿
