Returning to running after an ACL injury is a watershed moment. It is a huge milestone that many ACLers look forward to for months during their recovery. Prior to surgery the doctor and PT explain it very simply: “You can start running again at 3-4 months and you can return to playing sports at 9-12 months”.  You may even have a follow-up with your surgeon around that time where he feels your knee, watches you do a step-down and “voila!” you are ready to run. Your PT may watch you do a couple of exercises or test your balance and decide it is time.

Unfortunately, the reality isn’t that simple. Many ACLers find when they are “cleared” to run that they aren’t prepared. They may feel like they are compensating or worse, they may develop an increase in pain, swelling, or even loss of mobility.

This article will take a deep dive on why many ACLers struggle when they first start to run, how they are often cleared to run, and what research says is the best way to get back to running after an ACL surgery.

How are most ACLers cleared to run ?

Many ACLers are taken through rehab without a clear understanding of what their criteria to return to run is. They are told the protocol allows them to start running at 3-4 months and are led to believe that this is an expectation or the norm. Once that time comes, they often trust that their PT has a criteria that they may be unaware of, but exists nonetheless. They often feel that by watching them move their PT is able to determine how strong they are and thus how ready to run they are.

 

 

Unfortunately, research shows this to be wholly untrue. A large scoping review that included 201 studies found that only 1 in 5 utilized any criteria beyond time from surgery to determine readiness to run (1). This fits with another study showing that even for clearance to return to sports time alone was the singular criterion 42% of the time (2).

In fact, nearly 50% of physical therapists do not assess quadriceps strength at all and of the ones who did, 33% used manual resistance of their hands which is notoriously inaccurate for assessing quad strength (4).

What about the “eye test?” Your PT has been watching you move and has years of experience… shouldn’t he be able to tell when you are ready to run?

 

 

Research also tells us this is not the case. A 2018 biomechanical study analyzing a bodyweight squat found that at 3 months ACLers placed 38% less load on their surgical quads compared to their nonsurgical quads (5). They also found that even at 5 months these ACLers placed 30% less load on their surgical quads. At 3 months, the load was often shifted to their nonsurgical side, however at 5 months most of the load was shifted to the glutes of their surgical side. Thus, these deficits in loading of the surgical quad did not significantly improve over time.

 

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Essentially these ACLers were figuring out different ways to unload their surgical side quads (even on an “easy” task) consistently throughout their rehab, despite the watchful eye of their PTs.

Even more damning, at 13 months post-op, ACLers showed a 17% decrease in loading their surgical side quads during a simple bodyweight squat compared to those who did not have an ACL injury (3). The authors in that paper concluded that “By observation, the exercise can appear normal, while the ACL-injured individual may use kinetic compensation strategies” (3).

 

Simply put: the “eye test” even when done by an expert clinician isn’t good enough.

 

What criteria should be used to return to run?

So we’ve established time alone is not good enough to determine when you are ready to run. We’ve also established that your PT can’t simply watch your workouts and determine that you are ready to run.

So, what is the best criteria to allow a successful return to running after ACL surgery? Quadriceps strength testing, plain and simple. A 2021 study established a cutoff value for quad strength of 1.45 NM/Kg of bodyweight as a significant indicator of success with initiating a run progression (7).

 

READ: QUADRICEPS ACTIVATION FOLLOWING SURGERY

 

Similarly, another study found that the kinematic forces across the knee in ACLers who had quad strength less than 80% of their nonsurgical side were significantly different than healthy controls (8). Whereas, in ACLers who had a higher level of quad strength symmetry those forces were indistinguishable from healthy controls.

 

Essentially this tells us that, running with less than 80% quad strength symmetry (QSI) increases the forces across the knee joint putting you at risk for pain, swelling, compensation, and over time potential damage.

 

Now what if you don’t have access to fancy testing equipment like an Isokinetic Dynamometer? Fortunately, there’s a study for that too!  Sinacore et al. investigated how 1 rep max testing on a leg press and a knee extension machine, as well as a fixed handheld dynamometer, compared to the gold standard isokinetic dynamometer. They found that the leg press was most likely to overestimate quad strength symmetry leading to ACLers being cleared to run before they were actually ready.

 

1 rep max testing on a knee extension machine limited to the range of 90-45 degrees was both the most accurate and easily accessible option. Even that had the potential to overestimate quad strength symmetry thus the researchers established a cut point of 83% strength symmetry to be used to clear ACLers to return to running via this method. Thus, as an ACLer, you should know even before you have surgery that to return to running confidently, you need to demonstrate quad strength symmetry of 83% on 1 rep max testing via the knee extension machine.

 

Other critical criteria for success with a run progression are (9):

• Effusion of trace or less
• Full hyperextension matching the other side
• A “quiet knee” that tolerates current exercise & daily loads without negative response

 

READ: EXERCISES PRIOR TO ACL SURGERY

While many protocols & recommendations discuss initiating a run progression at 3-4 months post-op, this should be viewed as the earliest possible timeline for running. In most cases, ACLers successfully meeting the above criteria in this timeline had both a hamstring graft as well as prehab that included establishing >80% strength symmetry prior to surgery.

 

Additional research has established that those with patella tendon grafts took 1.5 to 2.5 months longer to meet return-to-run criteria (10). This makes sense due to the effect harvesting a patella tendon graft has on the quadriceps ability to function. Quad tendon grafts have much the same effect thus we can logically conclude a similar delay in timeline.

 

Thus, if an ACLer did not establish >80% quad strength symmetry pre-operatively and had a quad or patella tendon graft expecting them to successfully run at 4 months post-op may be unrealistic.

Fortunately, earlier initiation of a run progression is not critical for success when returning to running or playing sports. Running prior to meeting the appropriate criteria, however, can prevent a successful return to running, sport, and even contribute to the long-term development of osteoarthritis.

 

READ: THE BEST EXERCISES FOR KNEE OSTEOARTHRITIS

 

Closing Thoughts

Many PTs & MDs allow ACLers to return to running after surgery based simply on the passage of time alone. While they often give the impression of having a criteria or being able to assess readiness to run via a watchful eye research has shown that in the absence of a true strength test, this is wholly inadequate. While isokinetic dynamometry is the gold standard, 1 rep max testing on a knee extension machine from 90-45 degrees is a suitable and more accessible option when utilizing the cut points established in the research. Thus, the criteria for an ACLer to successfully return to running includes:

 

• Quad strength symmetry of >83% strength symmetry (via 1 rep max testing on a knee extension machine)
• Effusion of trace or less
• Full hyperextension matching the other side
• A “quiet knee” that tolerates current exercise & daily loads without negative response

 

LEARN MORE ABOUT OUR KNEE PREHAB PROGRAM

 

References:

1. Rambaud AJM, Ardern CL, Thoreux P, Regnaux JP, Edouard P. Criteria for return to running after anterior cruciate ligament reconstruction: a scoping review. Br J Sports Med. 2018;52(22):1437-1444. doi:10.1136/bjsports-2017-098602
2. Burgi CR, Peters S, Ardern CL, et al. Which criteria are used to clear patients to return to sport after primary ACL reconstruction? A scoping review. Br J Sports Med. 2019;53(18):1154-1161. doi:10.1136/bjsports-2018-099982
3. Roos PE, Button K, van Deursen RW. Motor control strategies during double leg squat following anterior cruciate ligament rupture and reconstruction: an observational study. J Neuroeng Rehabil. 2014;11:19. Published 2014 Feb 28. doi:10.1186/1743-0003-11-19
4. Ebert JR, Webster KE, Edwards PK, et al. Current perspectives of Australian therapists on rehabilitation and return to sport after anterior cruciate ligament reconstruction: A survey. Phys Ther Sport. 2019;35:139-145. doi:10.1016/j.ptsp.2018.12.004
5. Sigward SM, Chan MM, Lin PE, Almansouri SY, Pratt KA. Compensatory Strategies That Reduce Knee Extensor Demand During a Bilateral Squat Change From 3 to 5 Months Following Anterior Cruciate Ligament Reconstruction. J Orthop Sports Phys Ther. 2018;48(9)
6. Roos PE, Button K, van Deursen RW. Motor control strategies during double leg squat following anterior cruciate ligament rupture and reconstruction: an observational study. J Neuroeng Rehabil. 2014;11:19. Published 2014 Feb 28. doi:10.1186/1743-0003-11-19
7. Iwame T, Matsuura T, Okahisa T, Katsuura-Kamano S, Wada K, Iwase J, Sairyo K. Quadriceps strength to body weight ratio is a significant indicator for initiating jogging after anterior cruciate ligament reconstruction. Knee. 2021 Jan;28:240-246. doi: 10.1016/j.knee.2020.12.010. Epub 2021 Jan 9. PMID: 33429149.
8. The effect of insufficient quadriceps strength on gait after anterior cruciate ligament reconstruction Lewek, Michael et al. Clinical Biomechanics, Volume 17, Issue 1, 56 – 63
9. Adams D, Logerstedt DS, Hunter-Giordano A, Axe MJ, Snyder-Mackler L. Current concepts for anterior cruciate ligament reconstruction: a criterion-based rehabilitation progression. J Orthop Sports Phys Ther. 2012 Jul;42(7):601-14. doi: 10.2519/jospt.2012.3871. Epub 2012 Mar 8. PMID: 22402434; PMCID: PMC3576892.
10. Smith AH, Capin JJ, Zarzycki R, Snyder-Mackler L. Athletes With Bone-Patellar Tendon-Bone Autograft for Anterior Cruciate Ligament Reconstruction Were Slower to Meet Rehabilitation Milestones and Return-to-Sport Criteria Than Athletes With Hamstring Tendon Autograft or Soft Tissue Allograft : Secondary Analysis From the ACL-SPORTS Trial. J Orthop Sports Phys Ther. 2020 May;50(5):259-266. doi: 10.2519/jospt.2020.9111. Epub 2019 Nov 27. PMID: 31775553; PMCID: PMC7196003.

 

About the Author

Tommy Mandala

[P]rehab Writer & Content Creator

Tommy Mandala is a Doctor of Physical Therapy, Board Certified Clinical Specialist in Sports & Orthopedics, and Certified Strength and Conditioning Specialist in New York City. He is the founder of ALL IN ACL, a digital coaching platform dedicated exclusively to helping ACLers return to the life they had before their injury with full confidence in their knee. Prior to that, he worked in the sports clinic at Hospital for Special Surgery, the #1 Orthopedic Hospital in the country. While there, he had the opportunity to hone his skills as an ACL specialist working closely with world-renowned surgeons and evaluating patients from all over the world. He completed his sports residency training at the University of Delaware where he had opportunities to work with many of their Division I sports teams as well as the Philadelphia 76’ers NBA G-league affiliate, the Delaware Blue Coats. He also trained at Champion Sports Medicine in Birmingham, Alabama where he had the opportunity to learn from researchers in the American Sports Medicine Institute. Currently, Tommy works exclusively with ACLers through his digital coaching model. While many of these clients are athletes, Tommy works with ACLers of all different abilities helping them to build the strength they need to overcome this unique injury. One of his favorite aspects of his job is taking active clients who have never been a “gym person” before and showing them the amazing things that happen when they learn to strength train.

Disclaimer – The content here is designed for information & education purposes only and is not intended for medical advice.