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Important Muscles to Target in an ACL Rehab Program

Following an ACL tear or surgery, there are many pieces of the rehab puzzle that must be included to capitilize upon your knee’s resilient capabilities. The core, glutes, hamstrings, and quads are all going to be crucial muscles to strengthen in an ACL rehab plan, but today’s blog will hone into two of the dominant leg muscles prioritized in ACL rehab: the quads and hamstrings.

Common questions we get from patients at Made 2 Move following an ACL injury include: Why do I need to strengthen the quads and hamstrings specifically? How do I know if my quads and hamstrings are strong enough? How do I strengthen my quads and hamstrings? Let’s dive in.


The quadriceps (or quads for short) are a group of four muscles on the front of your thigh. These muscles are the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The quads are responsible for actively extending (straightening) the knee and flexing (bending) the hip.

A 2016 meta analysis looked at the effect of ACL tears on lower limb muscle strength and found, “reduction in quadriceps muscle strength was about 3-times greater than the reduction in hamstring muscle strength” (Hyung-Jung 2016). Because the knee is often held in an extended position post surgery, the ask on the quads is less during this down time, so they don’t have to work as hard. The good news? The quads, like any muscle in our body, are incredibly adaptive to training. As soon as you start turning them on again, they will jump into gear to get your knee back to optimal functioning.

One of our favorites, Move Strong PT in Hudson, MA, posted a recent blog on quad exercises after ACL tear. At Made 2 Move, our therapists incorporate these and other exercises progressively through the rehab process to build strength and confidence back into your knee.


The hamstrings are a group of three muscles on the back of your thigh. These muscles are the biceps femoris,semimembranosus, and semitendinosus. The hamstrings are responsible for actively extending the hip and flexing (bending) the knee.

The job of the ACL is to prevent excessive anterior translation (movement) of the tibia (shin bone) relative to the femur (thigh bone). Strengthening the hamstrings serves to complement this vital role of the ACL. Think of the hamstrings as the ACL’s sidekick: the stronger the hamstrings are, the less likely it is that injury will occur to this ligament. Benjamin Wright, an Australian PT writes, “The hamstrings not only act to bend the knee, but they also pull the tibia posteriorly (backwards), hence serving as a dynamic protector of the ACL and reducing strain on the ligament” (Wright 2017).

Why do we lose strength after ACL rehab?

A major reason for the decrease in muscle strength seen in the quads and hamstrings post injury could be due to arthrogenic muscle inhibition or AMI. Defined by research by Rice and colleagues in 2010, “Arthrogenic muscle inhibition (AMI) is the inability to fully contract a muscle despite the muscle not having sustained tissue damage” (Larson et. al 2021). Following injury, patients wonder, “My ACL is the structure that was injured, not my quads or hamstrings, so why do I feel like my muscles are weaker?”

While not fully understood, AMI could be the result of swelling, inflammation, pain, and neurological alterations. This is common not just in our ACL population, but anyone following an injury. The body goes into “protect” mode and one of the ways it does this is by dialing down the activation of muscles around the site of injury.

How do we test your strength?

The strength of the quads and hamstrings is more than just your PT pushing against your leg and asking you to resist it. This is a common test in PT, but at Made 2 Move, we aim to address the system as a whole. We must get away from seeing the body as a collection of parts. Your quad can work in isolation, sure, but to perform at their highest level, they need to be able to fire and contract harmoniously with other muscles to stabilize and exert force.

Your Made 2 Move therapist may simply ask you to contract your quads and hamstrings on the first day to see if the motor coordination and muscle activation is there. From there, we will progress to resisted strength testing (us asking you to resist our force), and eventually to more functional and sport specific strength tests.

These tests may look like squats or single leg exercises. Or it may look like one of the movements you do for your sport. Regardless of the test, our goal is to see how you are moving. We will ask how you are feeling about the movement. Building confidence in your knee is a major psychological component of the Made 2 Move ACL Rehab Program and building strength through the quads and hamstrings contributes to this.

How do we strengthen the quads and hamstrings?

The first step at the Made 2 Move ACL Performance Lab in strengthening the quads and hamstrings will include motor control and reeducation of the quadriceps and hamstrings muscles. Pain will often cause muscles to not fire in a harmonious way. Pain can also cause our muscles to dial down their activation. The point of early quad and hamstring strengthening drills is to dial back up their activation.

Our Made 2 Move therapists help train motor control of the muscles around your knee and progress to more intense strengthening and eventual plyometric and sport specific exercises.

The Made 2 Move team will also incorporate core exercises into your ACL rehab. Having adequate core stability helps you decelerate, jump and land with proper form. If you are strong through your midline, the rest of the body follows.

We cannot isolate ACL rehab to a single or even a few muscle groups. We must strengthen everything from the muscles around the ankle to the core muscles. The good thing? There are multi-joint exercises our Made 2 Move therapists prescribe that can kill multiple birds with one stone. (ie: strengthen multiple muscle groups with one exercise).

We know the quads and hamstrings must be strong, but in returning to optimal functioning and sport, they also must fire appropriately. Summarized beautifully by a 2021 research article on ACL rehab, “The physical demands inherent to sport performance require the integration of multiple physiologic systems into movement solutions that satisfy task demands” (Larson et. al 2021). Stated in a simpler way, the physical demands (running, jumping, cutting) needed for your sport (soccer, basketball, football, lacrosse) require multiple systems (neural, muscle, tendon, psychological) into rehab plans that help reach your goal.

The Made 2 Move ACL Performance Lab

Following an ACL injury or reconstruction, patients often are eager, but hesitant to get started with PT. This hesitancy is often due to pain or fear surrounding any sort of knee movement. Here at Made 2 Move, we are ready to be alongside you from the beginning to end of your ACL rehab. Come see us today! Email today kickstart your ACL rehab with one of our physical therapists or athletic trainers.


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