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Early Open-Chain Knee Extensions Done Safely

If I had a dollar for every time I’ve been asked, “When do you start open-chain knee extensions after ACL injury or reconstruction?”… well, I’d probably have enough money in the bank to retire early.

Here’s the thing: most of us were trained with a healthy fear of open-chain knee extensions (OKEs) - including myself!

I avoided knee extensions in my ACLR rehab programs for the first 5-6 years of my career - because that’s what I was told at university and by the people around me.

To be absolutely clear - that caution was reasonable for its time.

But when you line up what we do in the real world (encouraging early weight-bearing gait) with what we avoid in rehab (light, well-controlled knee extensions), the math doesn’t add up.

This post is me opening the clinic door and saying: here’s exactly how I run open chain knee extensions - timing, angles, sets/reps, progressions, safety guardrails, and how I explain it to patients.

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Don’t have time for the full 10min read?

I start isometric open-chain work as soon as the knee can bend to ~90° (post-injury and post-op), and I layer in isotonic OKEs from about week 4, using either full ROM with light load or 45–90° with heavier load. From 12 weeks onward I build strength like I mean it, always pairing open-chain with a quality closed-chain program and using PFJ tolerance and effusion response as my governors.

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For those of you still with me. Let’s begin with when..

When? As soon as the knee can flex to ~90°. That’s my green light post-injury and post-op to start with early isometrics with my attempt to “wake up the quad”.

Angles: 60° and 90° knee flexion.
Dose: Start 3×5 holds at each angle → progress to 3×10 if comfy.
Hold time: 3–5 seconds (I nudge them toward 5 s).
Pain target: 0–2/10 during holds.
Frequency: 2–3×/day, with 1–2 rest days/week so they don’t burn out mentally or stir up the joint.

Why isometrics first? Early on, muscle inhibition is the bully in the schoolyard. Isometrics are your quiet bouncer: they reduce pain sensitivity, promote voluntary activation, and set you up for success when you move into isotonic sets.

Add Biofeedback if you can

I’m a big fan of force biofeedback (e.g., VALD Dynamo). I’ll prop the tablet up, set the angle, and give them a live force target. Magic happens when patients see the number climb:

• It keeps effort honest without chasing pain,

• It turns “I think it’s working” into “I just hit 15% more than last time”,

• It normalises the first 3–4 weeks where AMI is the loudest voice in the room.

Clinician tip: Record the best 3-second average at 60° and 90° each session. Patients love watching those bars inch up. So do I.

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Onto Phase 2: Adding movement and load