5 Reasons ACL Rehab Takes So Long

5 Reasons ACL Rehab Takes So Long

ACL , Education , Kinetic

One of the first questions after an athlete has an ACL injury, is “how long until I can play again?” The truth is, it is a frustratingly long process (typically 9-12+ months). Here are 5 reasons why ACL rehab takes so long, and why this process shouldn’t be rushed.

1. ACL healing

The first reason why ACL rehab takes so long is the simple fact that your new ACL needs substantial time to heal and remodel to be a robust ligament like it was in the first place. Believe it or not, this process takes 1-2 years to fully take over. The healing process generally consists of 3 stages: Early, Proliferation, and Maturation. The Early Stage consists of necrosis, or a process in which cells die. This process is a signal for growth factors that lead to the next stage: “Proliferation.” This is where we get vascularization or blood supply and new cells growing. Lastly is a “Maturation” stage in which the cells remodel over and over to resemble a ligament. 

Studies showing different lengths of maturation of the ACL ligament after surgery.

Grafts going through early, proliferation, and maturation phases.

If you had an ACL reconstruction, they likely either used your patellar tendon, quad tendon, or hamstrings tendon as your new ACL. Tendons and ligaments are alike, but not the same. In order for the tendon to heal and behave like an ACL, it has to remodel or go through a “ligamentization” process so its properties are more like a true ligament. Rushing back to too intense of activities could put your healing ACL at risk.

2. Neuromuscular control – building back correct movement patterns without compensation

A normal ACL provides stability to the knee joint, but it also provides input to your brain on body awareness, or proprioception. This is essentially the ability to know where your limb is in space without needing to look at it. When we have an injury to the ACL, this input to your brain is altered. In order to gain back this awareness, it needs to be trained. This is what is commonly referred to as “neuromuscular control” training. Things like single leg balance drills might be one example, another being dual task strategies. These drills try to distract you and get your mind on one thing while trying to have your brain control your movement subconsciously. Another aspect of “neuromuscular control” that needs to be trained is training your body to move optimally with minimal compensations so that you can move safely and efficiently in your training and sport. The body is really smart, and, because of your injury/surgery, it tries to protect the injury at all costs. One way it does this is by altering how you move to make it “easier” on your knee. Although good and protective, it can also be counterproductive when our goal of rehab is to progressively load your knee so it can adapt and get stronger/more resilient to handle harder and harder tasks. So, we need to properly train your body to move in ways that DO load your knee, fighting against when your nervous system may try to protect.

3. Deconditioning 

Another reason ACL rehab takes so long is because there was a surgery and trauma, we do need to have relative rest. This means we can’t train the way you used to as an active athlete. Because you are not training really hard, there is going to be some level of deconditioning that takes place throughout the body. Cardiorespiratory fitness goes down, the ability to repeatedly produce high intensity efforts goes down, and your ability to withstand longer workouts as well as your ability to recover between workouts. Although we want to reduce how deconditioned you get by providing safe options for conditioning like biking, swimming, elliptical training, or upper body conditioning when it is safe to do so, it still takes time to fully recover general and specific fitness for your sport.

4. Strength 

If you have had or know anyone that has had ACL surgery, it probably isn’t surprising to see here that gaining strength is a huge goal, specifically of the quadriceps. Initially after ACL surgery (especially if they use a patellar or quad tendon graft), it is challenging to get the quadriceps to even contract at all. This is due to several reasons as a result of the ACL injury, surgery, and pain. When we start from ground zero to simply regain the ability to use the muscle, we do lose strength and it takes a surprisingly long time to fully recover this quality. What takes even longer than that is being able to use the muscle forcefully and quickly (power). This is a must when returning to most sports in which doing things fast is required. This is another trainable quality, but challenging to gain back quickly. For more information check out our blog on this topic

5. Risk of Injury

The last reason ACL rehab takes so long is that more and more data comes out demonstrating that early return to sport increases the risk of a second injury relative to later return. Some studies have shown that each month an athlete delayed their return until 9 months after surgery reduced the risk of another injury by about 50% and another that a group of athletes that returned to sport prior to 9 months had 7x higher re-injury rates than those that delayed their return. Any time an athlete returns to sport, there is always some level of risk that an injury may occur, but it is highly recommended that being patient and waiting until at least 9 months to return may decrease your risk of that injury. 



Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. Br J Sports Med. 2016 Jul;50(13):804-8. doi: 10.1136/bjsports-2016-096031. Epub 2016 May 9. PMID: 27162233; PMCID: PMC4912389.

Beischer S, Gustavsson L, Senorski EH, Karlsson J, Thomeé C, Samuelsson K, Thomeé R. Young Athletes Who Return to Sport Before 9 Months After Anterior Cruciate Ligament Reconstruction Have a Rate of New Injury 7 Times That of Those Who Delay Return. J Orthop Sports Phys Ther. 2020 Feb;50(2):83-90. doi: 10.2519/jospt.2020.9071. Erratum in: J Orthop Sports Phys Ther. 2020 Jul;50(7):411. PMID: 32005095.