Are Knee Extensions BAD After ACL Reconstruction? What the Research Actually Says
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In this live webinar for FPF Insiders Academy, we go over "Are Knee Extensions BAD After ACL Reconstruction? What the Research Actually Says":
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:
Extend that knee baby!
- Dan Pope DPT,OCS,CSCS
Show Notes / Relevant Articles:
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Thank you!
Dan Pope DPT, OCS, CSCS
References:
Optimising the Early-Stage Rehabilitation Process Post-ACL Reconstruction. Sports Medicine. 2024. Buckthorpe M, Gokeler A, Herrington L, et al.
Forelli F, Barbar W, Kersante G, Vandebrouck A, Duffiet P, Ratte L, Hewett TE, Rambaud AJM. Evaluation of Muscle Strength and Graft Laxity With Early Open Kinetic Chain Exercise After ACL Reconstruction: A Cohort Study. Orthop J Sports Med. 2023 Jun 27;11(6):23259671231177594. doi: 10.1177/23259671231177594. PMID: 37441511; PMCID: PMC10334004.
Forelli F, Mazeas J, Korakakis V, Ramtoola H, Vandebrouck A, Duffiet P, Ratte L, Kakavas G, Bouzekaroui Alaoui I, Douryang M, Bjerregaard A, Riera J, Rambaud AJM. Criteria-Based Decision Making for Introducing Open Kinetic Chain Exercise after-ACL Reconstruction: A Scoping Review. Sports Med Open. 2025 Apr 12;11(1):37. doi: 10.1186/s40798-025-00843-8. PMID: 40220107; PMCID: PMC11993518.
Should Return to Sport be Delayed Until 2 Years After Anterior Cruciate Ligament Reconstruction? Biological and Functional Considerations. Sports Medicine. 2017. Nagelli CV, Hewett TE.
Graft Intra-Articular Remodeling and Bone Incorporation in ACL Reconstruction: The State of the Art and Clinical Implications. Journal of Clinical Medicine. 2022. Moretti L, Bizzoca D, Cassano GD, et al.
Effects of and Response to Mechanical Loading on the Knee. Sports Medicine. 2022. Logerstedt DS, Ebert JR, MacLeod TD, et al.