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Are knee extensions bad after ACL reconstruction?
For years, clinicians have been told to be careful with open kinetic chain knee extensions after ACL-R because of concerns about anterior tibial translation, ACL graft strain, and potentially increasing graft laxity.
But does the research actually support avoiding knee extensions?
In this video, I break down the evidence on **open kinetic chain knee extension after ACL reconstruction** and, more importantly, how I think physical therapists should actually apply this information in the clinic.
We’ll cover:
• Why knee extensions place strain on the ACL graft — and why that isn’t necessarily a bad thing
• Open vs. closed kinetic chain ACL loading
• Why restoring quadriceps strength is so important after ACL-R
• Research comparing closed-chain rehab with combined open + closed-chain strengthening
• Whether early knee extensions actually increase ACL graft laxity
• How range of motion changes ACL strain during knee extension
• Why walking may actually strain the ACL more than lightly loaded knee extensions
• How graft ligamentization should influence our thinking
• Criteria for introducing open kinetic chain strengthening
• How I progress quad loading during the first 4+ weeks after ACL reconstruction
• Where BFR, isometrics, squats, and supine knee extensions fit into the progression
The big takeaway?
**Knee extensions aren't inherently “bad” after ACL reconstruction.**
The more useful question is:
**When should we introduce them, through what range of motion, with how much load, and does the knee currently tolerate that stress?**
We need to respect graft biology, joint effusion, range of motion, the graft harvest site, and the patient's overall irritability — while also recognizing that being too conservative with quadriceps strengthening can create its own problems.
If your athlete is several months into ACL rehab and still has a massive quadriceps deficit, simply avoiding knee extensions probably isn't helping them.
This is where criteria-based progression matters.
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⏱️ **TIMESTAMPS**
00:00 – Are Knee Extensions Bad After ACL Reconstruction?
01:28 – Open vs. Closed Kinetic Chain Exercises
03:22 – Why Clinicians Worry About Early Knee Extensions
04:40 – Why We NEED Open Kinetic Chain Strengthening
05:10 – Quad Strength & Knee Re-Injury Risk
07:01 – What the ACL Rehab Consensus Recommends
08:09 – Early Knee Extension Research After ACL-R
10:32 – Starting Knee Extensions at 4 Weeks
13:00 – A Major Limitation of the Research
16:03 – Quad Strength Results: Open vs. Closed Chain
17:09 – Hamstring Strength Results
18:13 – Did Knee Extensions Increase ACL Graft Laxity?
18:43 – Criteria for Starting Open Kinetic Chain Exercise
20:30 – How Early Can We Start Knee Extensions?
22:18 – Walking vs. Knee Extension ACL Strain
24:13 – Using ROM to Reduce ACL Graft Strain
25:34 – When Is the ACL Graft Actually Weakest?
29:38 – Quad-Biased Squats After ACL Reconstruction
31:41 – Closed Chain Doesn't Automatically Mean “Safe”
32:50 – Supine Knee Extensions for ACL Rehab
33:45 – BFR + Low-Load Quad Strengthening
36:09 – Weeks 0–2: Practical Quad Progressions
38:21 – Weeks 2–4: Progressing Knee Extensions
39:00 – Week 4+: Loading the Quadriceps Harder
40:08 – Final Clinical Takeaways
If you’re a physical therapist, athletic trainer, strength coach, or other rehab professional working with ACL reconstruction patients, let me know in the comments:
**When are you currently introducing knee extensions after ACL-R?**
And if you have another rehab question you want me to break down, drop that below too.
#ACLRehab #ACLReconstruction #PhysicalTherapy #KneeRehab #QuadricepsStrength #SportsPhysicalTherapy