Quad Rehab After ACL'r (Part 1)

Sports Med U | Educating Minds, Elevating Potential

Oh, My Quad: A Clinical Commentary And Evidence-Based Framework for the Rehabilitation of Quadriceps Size and Strength after Anterior Cruciate Ligament Reconstruction

Solie, B., Carlson, M., Doney, C., Kiely, M. and LaPrade, R., 2024. Oh, My Quad: A Clinical Commentary And Evidence-Based Framework for the Rehabilitation of Quadriceps Size and Strength after Anterior Cruciate Ligament Reconstruction. International Journal of Sports Physical Therapy, 19(12), p.1600..

In today’s letter

• Overview of quad re-awakening after ACLR

• Clinical tips and loading framework

• A fun infographic for you to save and use in the future

• 3 resources to check out to further your knowledge about the quads

• Meme of the week: Rest is for the weak 👀

• Rapid Results =

After ACL reconstruction, restoring quadriceps strength requires more than just generic strengthening—it demands precise loading based on muscle architecture, contraction type, and the specific graft chosen.

• Professional Takeaway =

Using overcoming isometrics early in ACLR rehab to counteract AMI and rapidly re-establish quadriceps recruitment is step numero uno. Progress to heavy-slow resistance training and eccentric quasi-isometrics to build tendon load tolerance without provoking graft-site pain.

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Aim of the study

The purpose of this commentary is to integrate the existing muscle basic science and strength training literature into a best-evidence synthesis of exercise methodologies for restoring quadriceps size and strength after ACLR

Did you know?

ACL tears are common—no surprise there—and ACLR is the gold standard for getting people playing sports (no matter if its weekend warrior or a pro) . But not all ACLRs are created equal.

The choice of graft matters, especially when it comes to how the quads bounce back.

• Hamstring tendon (HT) autografts are the most widely used globally.

• Quadriceps tendon (QT) and bone-patellar tendon-bone (BPTB) grafts are gaining traction—especially QT.

There are pros and cons for both, however, using the quad or patellar tendon can cause more arthrogenic muscle inhibition (AMI)—which in the simplest form means the nervous system puts the brakes on quad activation post-surgery.

A very familiar experience for physios.

Why Its Critical To See The Quads Comeback

Persistent quad weakness is a major barrier to full recovery and considered to be more than just nuisance.

We’re talking:

• Poor knee biomechanics

• Slower progress through rehab milestones

• Lower return-to-sport rates

• Less patient satisfaction

• Increased risk of early-onset knee osteoarthritis

Not exactly what your athletes signed up for.

What You Can Do About It

As a physio, your job is twofold:

1. Address AMI – Get that neuromuscular system back online. Think neuromuscular stimulation, blood flow restriction training, and progressive motor control work.

2. Rebuild Strength and Size – Tailor your programme to rebuild atrophy and rewire motor patterns for high-performance.

🧠 Pro tip: Treat the brain as much as the muscle—AMI is a central nervous system problem at its core

Understand The Quads

The quadriceps are a group of four muscles:

1. Rectus femoris – the only biarticular muscle (crosses both the hip and knee)

2. Vastus lateralis

3. Vastus intermedius

4. Vastus medialis

They all insert via the patellar tendon into the tibial tuberosity, working together to extend the knee. The rectus femoris, with its origin on the anterior inferior iliac spine, also contributes to hip flexion and features an intramuscular tendon for energy transfer—especially important in high-velocity moves like kicking or sprinting.

💡 To target the rectus femoris specifically, use exercises combining hip flexion and knee extension— like SLRs or running/kicking drills

Following ACL reconstruction—especially when using bone-patellar tendon-bone (BPTB) or quadriceps tendon grafts—arthrogenic muscle inhibition (AMI) can seriously limit quad activation.

This results in:

• Persistent quadriceps weakness

• Poor knee biomechanics

• Slower rehab progression

• Lower return-to-sport rates

• Increased risk of early knee osteoarthritis

That’s not all. The quads have a high volitional recruitment threshold, meaning they’re already hard to activate—let alone post-surgery when neuromuscular control is compromised.

Fibre-Type Distribution & Recovery

• Vastus lateralis: ~50% Type II fibres → powerful, but recovers relatively quickly

• Rectus femoris: ~62% Type II fibres → fatigues faster, needs 72–96 hours between high-intensity sessions

👉 This means the single-joint muscles (vastus group) can tolerate more frequent training (every 48–72 hours), while biarticular rectus femoris needs more rest.

The Length Tension Relationship

Muscles produce more force at optimal sarcomere lengths.

Here’s what we know:

• Rectus femoris: Operates on the ascending limb of the curve. It loses force when trained in high hip flexion + knee extension (e.g., seated knee extensions at 90° hip flexion). Avoid this combo to prevent active insufficiency.

• Vastus group: Best loaded at longer muscle lengths (60°–140° knee flexion)

  • Vastus intermedius: Half squats (0–90°) for maximal activation

  • Vastus medialis/lateralis: Deep squats (90°–140°) to hit the descending limb of their curve and drive regional hypertrophy, especially distally

The Internal Moment Arm

The internal moment arm (IMA) is essentially how well a tendon can create torque at a joint.

• Patellar Tendon IMA:

  • Increases from 0° to 30° of knee flexion (peak torque potential).

  • After 30°, the moment arm gradually declines.

  • → Best loaded early in range (0–30°) to maximise torque without excessive strain.

• Quadriceps Tendon IMA:

  • Remains relatively constant from 0–25°, peaks around 20°.

  • As flexion increases past 30°, force transmission actually increases, even though the moment arm decreases.

  • Why? Passive tension in the muscle-tendon unit increases, helping transfer more force.

👉 Rehab Tip:

• To preferentially target the patellar tendon, start loading in shallow ranges.

• To load the quad tendon, work into deeper flexion—but be cautious if pain is present.

Contraction Modes

The way a muscle contracts isn’t a rehab detail—it’s a rehab strategy.

Different contraction modes stimulate different physiological responses, and when applied properly, they can accelerate strength, reduce pain, and even recalibrate the nervous system after ACL reconstruction.

Let’s break it down:

1. Isometric Training:

Traditionally associated with early post-op rehab, isometric training is far more than just a placeholder until dynamic movement returns. It’s incredibly effective at preserving and rebuilding strength, modulating pain, and increasing motor control across all stages of rehab.

There are two distinct types of isometrics—and they serve different purposes.

🟣 Overcoming (Pushing) Isometrics

• These involve pushing against an immovable object, like trying to extend the knee against a fixed bar.

• The body recruits high-threshold motor units, generating maximal voluntary contraction (MVC).

• This results in greater peripheral muscle activation, targeting the neuromuscular system aggressively to rebuild strength and hypertrophy.

• Time to fatigue is typically longer, and the nervous system learns to "up-regulate" output.

📚 Science says: Overcoming isos improve motor unit recruitment, increase cross-sectional area, and are especially beneficial in overcoming AMI by re-establishing strong corticospinal drive (Rio et al., 2015).

✅ Use when the goal is:

• Maximising strength

• Overcoming neural inhibition

• Stimulating hypertrophy post-atrophy

🟢Yielding (Holding) Isometrics

• These involve maintaining a static position under load, like holding a wall sit or static lunge.

• They often mimic eccentric contractions in their neuromechanical profile.

• Less peripheral activation, but more neuromuscular coordination and central motor control is involved.

• Typically induces faster fatigue due to longer time under tension and more complex cortical engagement.

📚 Why it matters: Yielding isos behave like a hybrid between concentric control and eccentric lengthening. They are shown to modulate tendon pain, reduce symptoms of AMI, and retrain motor control without overloading healing tissues.

✅ Use when the goal is:

• Reducing pain (especially tendinopathy-related)

• Early-stage motor re-education

• Managing AMI and central inhibition

2. Eccentric Training:

Eccentric contractions (lengthening under load) are a cornerstone in ACL rehab, and here's why:

• Eccentric strength is ≈41% greater than concentric (Rutherford et al., 2001).

• At any given force output, eccentric contractions require less metabolic energy and lower EMG activation than concentric work (i.e., more efficient).

• They produce high mechanical tension, a primary driver of muscle adaptation.

• They promote fascicle lengthening and sarcomere addition, changing muscle architecture in ways that reduce re-injury risk.

💡 Rehab value? Improved tissue resilience, enhanced load tolerance, and return-to-play readiness

Eccentric Quasi-Isometrics (EQIs):

EQIs are the perfect bridge between static and dynamic loading. Imagine a patient holding a squat isometric until fatigue slowly pulls them into a controlled eccentric descent.

• Starts as yielding isometric, ends as eccentric.

• Allows for high-load exposure while protecting tissues within a controlled ROM.

• Causes less post-exercise soreness than traditional eccentric sets (McHugh et al., 2002).

• Promotes both neuromuscular adaptation and tendon resilience.

Best used when:

• Patient can tolerate load but isn't ready for full eccentric dynamics

• You want eccentric benefits without the DOMS

• A controlled increase in load is needed without risking graft or tendon irritation

3. Heavy-Slow Resistance Training (HSRT): The Tendon Whisperer

HSRT has come out as one of the most effective interventions for tendinopathy, especially at the patellar and quadriceps tendon autograft sites post-ACLR.

• Utilises 70–100% of concentric 1RM at slow tempos (e.g., 3–6s concentric/eccentric phases).

• Increases time under tension, which enhances collagen remodelling and tendon load capacity.

• Encourages intramuscular force production through the full ROM without the ballistic risk of fast lifting.

📚 Why it's gold: HSRT has been shown to reduce pain, improve tendon stiffness, and restore load-tolerance—especially in patients with chronic graft-site symptoms (Kongsgaard et al., 2015).

✅ Best used when:

• Patient is mid-to-late rehab stage

• Tendinopathy is present at graft harvest site

• You want strength gains without reactive symptoms

Clinical Tip

Different contraction modes give different physiological benefits. Knowing when and how to use them turns your ACL rehab from basic to brilliant. Load isn’t the enemy—misapplied load is.

👇👇👇

When to Use What?

Top 3 Resources to Check Out

And learn more about the quads!

1. Rehab ideas for the quad post ACL’r (Article) - Link 🏋

2. Arthrogenc muscle inhibition (AMI) and EMS - (Webinar)

Meme of The Week

When You’re Ready to Learn More

We have great resources for you to devourer

1. Killer Articles —> Literally everything you need to know about a specific injury

2. Tendinopathy 4 phase rehab frame work - My book that walks you through a step by step process of treating tendons

3. Tendininopathy Specific Guides - Learn how to diagnose and manage patellar, achilees, elbow and many more tendinopathies

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