Should We Still Avoid Open Chain Exercises After an ACL Reconstruction? Research Review
Key insights: 60-second read
- Open kinetic chain exercises (OKC) are safe after ACL reconstruction - The long-standing concern that they compromise the graft may be outdated. Research shows no increase in graft failure when they are introduced appropriately.
- The best time to start is 4-6 weeks after surgery - Starting OKC exercises in this window, after a period of closed kinetic chain (CKC) work, provides the greatest benefits for strength and function.
- OKC exercises improve quadriceps and hamstring strength - They are particularly effective for restoring the strength deficits that commonly persist after ACL reconstruction.
- The traditional "closed chain only" approach may be outdated - Combining both exercise types appears to produce better outcomes than either approach alone.
If you've had an anterior cruciate ligament (ACL) reconstruction, you've probably heard a little about what exercises you should/should not be doing during your recovery. As a Physio, One of the most common I've had rolling around inside my head for decades is that you should avoid "open chain" exercises - like leg extensions - because they might put too much stress on your new graft.
This belief has been around since the 1980s, and it has shaped how many physiotherapists and surgeons approach ACL rehabilitation. For years, the standard approach was to focus almost exclusively on "closed chain" exercises like squats, leg presses, and step-ups, while avoiding exercises where the knee moves without the foot in contact with the ground.
But is this approach actually supported by the evidence? A new systematic review and meta-analysis published in Physical Therapy in Sport has examined this question in detail. The researchers analysed 14 studies involving 729 participants to determine whether open kinetic chain exercises are safe and beneficial in the early weeks after ACL reconstruction. Let us break down what they found and what it may mean for your recovery.
On this page
1. What Are Open and Closed Chain Exercises?
Before we dive into the research, let us clarify what these terms actually mean.
Closed Kinetic Chain (CKC) Exercises
The foot of the limb is fixed to a stable surface. Your foot stays in contact with the ground or a machine. Examples include:
- Squats
- Leg press
- Step-ups
- Lunges
- Wall squats
Open Kinetic Chain (OKC) Exercises
The end of the limb is free to move. Your foot is not fixed to a surface, and the movement involves only one joint. Examples include:
- Leg extensions (knee extension machine)
- Hamstring curls
- Straight leg raises
- Seated knee extensions
The key difference is that in CKC exercises, multiple joints work together, and the forces are shared across the whole chain. In OKC exercises, the force is more isolated to a single joint - in this case, the knee.
2. The Traditional Concerns: Why Were OKC Exercises Avoided?
The concern about OKC exercises after ACL reconstruction goes back several decades. The thinking was that when you do a leg extension, the force is transmitted directly to the knee joint. This creates shear forces that might directly pull on the graft, potentially leading to graft failure or increased knee laxity.
Because of this concern, the standard approach in many rehabilitation programs was to avoid OKC exercises entirely, especially in the early weeks after surgery. The focus was instead on CKC exercises, which were believed to be safer because:
- The compressive forces through the joint provide more stability
- Multiple muscles work together, reducing isolated stress on the graft
- The foot being fixed means the forces are distributed differently
However, the researchers behind this new study point out that these concerns "may be outdated, as the stress imposed by OKC exercises may be equal to that imposed by daily activities or other strengthening exercises".
3. What the New Research Shows
The systematic review included 14 studies with 729 participants and analysed 31 different outcomes. The researchers found that OKC exercises had beneficial effects on:
- Patient-reported outcomes (PROMs): People who did OKC exercises reported better function and quality of life, as measured by scores like the IKDC.
- Strength: OKC exercises significantly improved both knee extensor (quadriceps) and knee flexor (hamstring) strength, particularly at eccentric and higher-speed contractions.
- Return to sport: People who did OKC exercises returned to participation, sport, and competition faster than those who only did CKC exercises.
The only disadvantage observed was a slight increase in knee laxity when OKC exercises were performed immediately after surgery and not combined with CKC exercises. However, this did not translate into actual graft failure.
Important Finding
When OKC exercises were performed after a period of CKC exercises (rather than instead of them), there were no adverse effects at all - and the benefits were even greater.
This is a crucial point. The research does not suggest that OKC exercises should replace CKC exercises. Instead, it suggests that combining both types - starting with CKC and then adding OKC - produces the best results.
4. When Should You Start OKC Exercises?
This is one of the most important questions for anyone recovering from ACL reconstruction. The research provides some clear guidance.
| Timing | Findings | Recommendation |
|---|---|---|
| Before 4 weeks | May increase knee laxity measurements, though not graft failure. Fewer benefits observed. | Generally not recommended, except in specific protocols under close supervision. |
| 4-6 weeks | Greatest benefits for strength, function, and patient-reported outcomes. No adverse effects. | Ideal window - best time to introduce OKC exercises after CKC foundation. |
| After 6 weeks | Benefits still observed, but may be delayed compared to starting at 4-6 weeks. | Still beneficial, but starting earlier (4-6 weeks) appears optimal. |
The researchers also looked at two studies that directly compared early (4 weeks) versus late (12 weeks) introduction of OKC exercises. They found that early introduction significantly reduced pain, with no disadvantages for other outcomes like laxity or strength.
A separate study found that introducing OKC hamstring exercises as early as 3 weeks after surgery was safe and promoted clinically meaningful improvements in strength and endurance. However, the researchers of the main review caution that starting before 4 weeks may increase laxity measurements, even if it does not cause graft failure.
5. Practical Takeaways for Your Recovery
So what does all this mean for you if you are recovering from ACL reconstruction? Here are the key takeaways:
- OKC exercises are not dangerous: The evidence shows they are safe when introduced appropriately. The concern about graft failure appears to be overstated.
- Start with CKC first: Build a foundation of closed chain exercises (squats, leg press, step-ups) before adding open chain exercises. This is the approach that produced the best outcomes in the research.
- Aim for the 4-6 week window: The best time to start OKC exercises appears to be around 4-6 weeks after surgery. This provides the greatest benefits without adverse effects.
- Use a limited range of motion: When starting OKC exercises, keep the range of motion limited (90-45 degrees of knee flexion) and progress gradually as your knee tolerates it.
- Combine both types: The best results come from combining OKC and CKC exercises, not choosing one over the other.
- Monitor your knee response: Pay attention to pain, swelling, and stiffness. If symptoms increase, reduce the volume or load and progress more gradually.
What about the type of graft? The researchers note that there is still limited evidence to determine the acceptable loads for different graft types. In the studies they reviewed, participants had various graft types (bone-patellar tendon-bone, hamstring, or mixed), and the results were generally consistent across them. However, more research is needed in this area.
What about range of motion? Current clinical practice guidelines recommend starting OKC exercises in a restricted range of motion (90-45 degrees of knee flexion). The studies in this review generally followed this approach, with most allowing progression to full knee extension by around 6-9 weeks. A scoping review found that clinical criteria like achieving 100 degrees of knee flexion, minimal swelling, and pain below 2-3/10 were also used to guide progression.
The traditional approach of avoiding open chain exercises after ACL reconstruction may be outdated. The evidence suggests that when introduced at the right time - after a period of closed chain work, around 4-6 weeks after surgery - OKC exercises are safe and provide significant benefits for strength, function, and return to sport.
This does not mean OKC exercises should replace CKC exercises. The best results come from combining both types, using CKC as the foundation and adding OKC to target specific muscle groups like the quadriceps and hamstrings.
If you are recovering from ACL reconstruction, discuss these findings with your physiotherapist. Every recovery is different, and the best approach depends on your individual situation, including your graft type, surgical protocol, and how your knee is responding to rehabilitation.
- Grant
Frequently Asked Questions
Are open chain exercises safe after ACL reconstruction?
Yes, the evidence suggests they are safe when introduced appropriately. The research shows no increase in graft failure when OKC exercises are performed after a period of CKC exercises, starting around 4-6 weeks after surgery. While starting before 4 weeks may increase laxity measurements slightly, this does not appear to translate to actual graft failure.
When should I start open chain exercises after ACL surgery?
The research suggests the best time to introduce OKC exercises is 4-6 weeks after surgery, following a period of CKC exercise. This provides the greatest benefits for strength, function, and patient-reported outcomes without adverse effects. Current clinical practice guidelines also recommend starting at 4 weeks postoperatively within a restricted range of motion (90-45 degrees of knee flexion).
What exercises are considered open chain?
Open chain exercises are those where the end of the limb is free to move. Examples include leg extensions (knee extension machine), hamstring curls, and straight leg raises. These exercises isolate a single joint - in this case, the knee.
Can I do leg extensions after ACL reconstruction?
Yes, but with appropriate timing and precautions. The evidence suggests that leg extensions (a common OKC exercise) can be introduced around 4-6 weeks after surgery, starting in a limited range of motion (90-45 degrees of knee flexion) and progressing gradually. Your physiotherapist should guide you on the appropriate timing and progression for your specific situation.
What is the difference between open and closed chain exercises?
In closed chain exercises, the end of the limb is fixed to a stable surface (like the ground or a machine), and multiple joints work together. Examples include squats, leg press, step-ups, and lunges. In open chain exercises, the end of the limb is free to move, and only one joint is involved. Examples include leg extensions, hamstring curls, and straight leg raises.
One key insight from this research
"The greatest benefit with no adverse effects was achieved when OKC was started after CKC, between 4 and 6 weeks after ACL-R. The long-standing concern that OKC exercises compromise graft healing appears to be outdated."
Reference
Fontanier, V., Vergonjeanne, M., Eon, P., Bruchard, A., & Laplaud, D. (2025). Effect of open kinetic chain exercises during the first weeks of anterior cruciate ligament reconstruction rehabilitation: A systematic review and meta-analysis. Physical Therapy in Sport, 72, 95-108. DOI: 10.1016/j.ptsp.2025.02.005
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