Oh My Quad! 🙏 How to Rehab Quads Post ACL'r (Part 2)

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

• How to rehab quads (phase by phase) after ACL reconstruction

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

• Meme of the week: Outpatients + Physio = Busy 😄 

• Rapid Results =

Successful ACLR rehab is progressive, with each phase designed to rebuild strength, neuromuscular control, and functional capacity. From initial quadriceps activation to high-intensity sport-specific movements, training should mirror the demands of the athlete’s return to play, making sure the recovery is safe and effective.

• Professional takeaway =

In the later stages of ACLR rehabilitation, prioritise eccentric-specific training and velocity-based exercises to improve quadriceps force production and rate-of-force development, mimicking the demands of high-level sports.

Rebuilding the Quads After ACLR

Every knee is different, especially after surgery. Whether your patient had a primary ACLR or a revision, the type of graft (hamstring autograft, allograft, etc.), and any other procedures done (like meniscus repairs) all contribute.

The protocols outlined in this paper are not a one-size-fits-all program. Rehab must be tailored, and updated as the patient progresses — not just once at the start.

Know the Risk Factors

Some things we can’t change, but we must respect them. These non-modifiable risk factors can make grafts more vulnerable to laxity or failure:

• Knee hypermobility

• Use of allograft or hamstring autograft

• Prior meniscectomy

• High tibial slope

If your patient ticks more than one of those boxes, be extra mindful.

For example: avoid open kinetic chain (OKC) quad exercises from 0–45° of knee flexion early on — that’s when ACL strain spikes. Stick to safer angles (45–100°+) until strength and stability catch up.

Rehab Is Science & Art

Quad exercises need to factor in:

• Surgical technique (not all ACLRs are created equal)

• Healing timelines (give biology time)

• Joint homeostasis (don’t irritate the joint)

• Patient preferences (compliance is needed)

Use objective tests like the sweep test and pain-monitoring model to track joint irritability.

Very Early Rehab - 0-3 weeks

let’s zoom in on the immediate post-op phase — the first 0–3 weeks after an ACL reconstruction. This is where we lay the foundation, and if we mess this part up, the rest of the rehab becomes a slog.

The goal: Get that knee straight, wake up the quads, and keep things moving — often and gently.

1. Restore Knee Extension Early (Immediatly)

First things first: full active knee extension is non-negotiable. Even a small loss can:

• Mess with knee joint mechanics

• Trigger arthrogenic muscle inhibition (AMI) — the nervous system literally puts the brakes on the quads

• Increase long-term risk of knee osteoarthritis

So, passive extension stretches, heel props, and quad sets should be done little and often

2. Why OKC Might Beat CKC in the Early Days

In these early weeks, open kinetic chain (OKC) exercises (like straight leg raises or short-arc quads) are more effective than closed kinetic chain (CKC) work.

Why?

Because:

• Quads are sleepy post-surgery

• OKC allows you to target them directly without loading the joint too much

• It helps lower the volitional threshold needed to activate fibres (or in simple terms - It makes it easier for the muscle fibers to activate on their own)

Bottom line: don’t fear OKC. Just stay within safe knee flexion ranges (typically 45–100°) and monitor for irritation.

3. Frequency

When intensity has to stay low, frequency steps up.

• Short, frequent sessions (5–6 times a day)

• Focus on activation, mobility, and low-load movements

• Encourage neuroplastic changes

Open vs Closed Kinetic Chain

The challenge after ACLR in quadriceps rehab is to rebuild force output without compromising graft integrity.

This requires a mindful mix of open kinetic chain and closed kinetic chain exercises that respect healing tissues & optimise biomechanics — particularly in the early stages.

Open Kinetic Chain Load Progression

Rehabilitation should begin with quadriceps setting, ideally in low hip flexion positions (i.e., trunk reclined), to optimise the length-tension relationship of the rectus femoris. Simultaneously, positioning the knee between 20–45° of flexion helps enhance the internal moment arm of the quadriceps, improving leverage and activation. This specific range is also useful in managing high levels of arthrogenic muscle inhibition, which is common post-surgery due to disrupted afferent signalling from the joint.

To improve motor recruitment, isometric holds should be prescribed for long durations (45–90+ seconds). This sustained contraction allows for better neuromuscular re-education, particularly when AMI limits voluntary activation. Superimposing neuromuscular electrical stimulation (NMES) during these exercises can accelerate recovery of quadriceps force output, especially early in rehab when voluntary drive is impaired.

As volitional control improves, progress to Straight Leg Raises.

Good execution is key: cue patients to initiate a maximal quad contraction into superior patellar glide, maintain external femoral rotation, and dorsiflex the ankle throughout the movement. These tweaks improve force transmission through the kinetic chain and prevent flexion lag. Start in tall sitting or standing, and progress to long sitting for increased difficulty.

Use blood flow restriction (BFR) or distal loading to increase metabolic stress and muscular fatigue with minimal joint load.

Finally, submaximal yielding or holding isometrics between 45–60° of knee flexion can target the quadriceps during the descending phase of the length-tension curve. This angle improves moment arm efficiency, enhances torque output, and importantly, reduces graft strain compared to more extended positions. It may also help downregulate anterior knee pain — particularly in patients with grafts harvested from the extensor mechanism.

Closed Kinetic Chain Load Progression

CKC progression starts with Terminal Knee Extensions in a seated position. These target the monoarticular quadriceps muscles (like the vasti group) and reduce shear forces at the knee joint.

They can be progressed by:

• Increasing band resistance

• Adding long-duration isometrics

• Incorporating BFR for enhanced fatigue and hypertrophy effects

Incorporating prone quadriceps set is also beneficial. Removing visual feedback challenges proprioception and enhances the sensorimotor system’s contribution to motor control — a vital aspect of long-term knee stability and injury prevention.

Together, these strategies form a robust framework for quadriceps load progression that is grounded in biomechanics, neurophysiology, and clinical best practice. The goal is simple: restore strength without compromising the healing graft — and to do it with science on your side

Early Rehab - 3-8 weeks

By now, we've usually regained active knee range of motion and volitional quadriceps activation — but the work is far from over.

The key in this phase is intelligent progression: loading the quadriceps in a way that respects biological healing & minimises joint irritability.

Blood Flow Restriction:

During this period, joint effusion and low-grade irritability often linger. This makes low-load training with blood flow restriction (BFR) an ideal tool.

Training at intensities <20% of concentric 1-RM with BFR can elicit hypertrophic and strength adaptations that are typically only seen with high-load resistance training.

• Frequency: 1–2 times daily

• Occlusion pressure: High, individualised to optimise the anabolic response

• Proximity to failure: Aim for 0–2 reps in reserve to maximise hypertrophy

• Key exercises: Combine OKC knee extensions with CKC TKEs for full-quadriceps recruitment, and include prone quad sets to hamstring curls to challenge posterior chain synergy

OKC Progression: From Yielding to Overcoming

Advance from yielding isometrics (45–60°) to overcoming isometrics (60–90°). This transition recruits more motor units and encourages regional hypertrophy in distal quadriceps — especially relevant for BPTB or QT autografts, where anterior knee pain may limit tolerance to dynamic work. NMES remains a valuable adjunct here for enhancing torque output.

CKC Progression: Reintroducing Weightbearing Wisely

• Start point: Double-leg squats at 45–60° flexion

• Volume: 3–6 sets of 45–90 sec submaximal holds, 2x/day with 6–8 hrs between sessions

• Goals: Improve motor recruitment, reduce tendon pain, and stimulate tendon repair via stress relaxation

Then progress to split squats, reducing reliance on the non-surgical limb to address inter-limb compensation. Advance again to front-foot elevated split squats, pushing into the 60–90° flexion range to increase loading and control

Mid Stage Rehab - 8 - 12 weeks

At this point, we’re still managing joint irritability and effusion, especially in those who had patellar tendon (BPTB) or quadriceps tendon (QT) grafts. But we’re also aiming to progressively load the quads in ways that promote hypertrophy and prepare for more dynamic phases ahead.

The Big Picture

One of the main strategies in this phase is increasing knee flexion angles during resistance training before increasing external load.

• Deeper flexion (45–100+°) enhances the length-tension relationship of the quadriceps, particularly useful for targeting the distal fibres.

• It also reduces ACL graft strain, especially compared to training in shallow ranges (0–45°).

• However, as you flex deeper, the force distribution between patellar and quadriceps tendons shifts, so for BPTB and QT grafts, monitor for anterior knee pain or localised irritation.

Open-Kinetic-Chain Progressions: Smart and Specific

This is the time to move past low-load isometrics and into more targeted resistance work:

• Train the quads through 45–100+° of knee flexion, unless limited by surgical precautions.

• Progress yielding/holding isometrics toward maximal effort holds. When these can no longer be sustained for more than 20–45 seconds, introduce EQI (Eccentric Quasi-Isometrics) — long-duration eccentric holds that build both strength and tissue tolerance.

• Start EQIs at 45–70° flexion, then progress to 70–120+° only if the knee tolerates it, as this range increases passive tension and internal quad forces.

Also consider combining isometrics with neuromuscular electrical stimulation (NMES) to maximise torque output during high-effort contractions.

Closed-Kinetic-Chain: Stability is Still King

In CKC, unilateral exercises with external stability are preferred — think leg press machines, supported split squats, or squats with TRX.

• Start with CKC yielding/holding isometrics at 45–90° knee flexion.

• Prescribe sets to volitional fatigue within 20–45 seconds, which triggers hypertrophy and improves motor unit recruitment.

• Use a decline wedge or heel lift to increase quad contribution during squats or lunges.

• Once maximal effort isometrics are tolerated well, progress to adding external load — but only at flexion angles the knee can comfortably handle.

Traditional Strengthening Phase - 12–24 Weeks

By 12 weeks post-ACL reconstruction, the graft has typically achieved a significant degree of biological integration, and the autograft harvest site (in cases of BPTB or QT) has remodeled into scar-like tendon tissue.

This remodeling phase significantly increases the load tolerance of both the graft and extensor mechanism, allowing the rehab process to fully transition into traditional, maximal-effort quadriceps strength training.

However, recovery still isn’t linear — careful monitoring of knee irritability, soreness, and fatigue is essential, and recovery must be dialed in as training intensity ramps up.

Open-Kinetic-Chain Load Progression: Max Load, Smart Speed

During this phase, OKC exercises continue targeting the quadriceps in isolation — now at true strength-building intensities:

• Maintain training in the 45–100+° range of knee flexion, where both ACL graft strain is minimized and distal quadriceps fibers are most effectively activated.

• Continue using EQI (eccentric quasi-isometric) contractions — hold maximal effort isometrics for 20–45 seconds and allow a controlled eccentric “yield” through deeper flexion.

• Introduce heavy-slow resistance training (HSRT) at loads exceeding 70–80% of the concentric 1-RM. This approach maximises mechanical tension at low velocities (<60°/sec), which enhances intramuscular force production and hypertrophy signaling.

These contraction modes (EQI + HSRT) are not only joint-protective, but they also generate high force without relying on high velocity, which is ideal for a recovering knee.

Closed-Kinetic-Chain Load Progression: One Leg, Heavy Loads

CKC progressions at this stage are aimed at improving force output under functional, weight-bearing conditions, especially through unilateral loading:

• Prescribe single-leg exercises that produce large external knee flexion moments (i.e., front-loaded split squats, rear-foot elevated split squats, or unilateral leg press).

• Use a decline wedge or heel lift to emphasise quadriceps contribution by increasing knee-forward translation and joint torque.

• Maximal yielding/holding isometrics can now be performed in deeper ranges (60–90+°) to increase muscle recruitment and tendon conditioning. Be mindful though — deeper flexion increases joint compression and shear, so symptom monitoring is key.

• EQI contractions on a leg press can be added: start with a maximal isometric hold at ~60° flexion, then resist the eccentric descent into deeper angles (90°+) for further loading.

• Introduce HSRT in CKC formats too, with sets structured to 4–6 reps max at loads that push close to failure — again staying in the 45–120+° range for optimal quad recruitment and minimal graft stress

Eccentric Strengthening / Power Phase - 24+ Weeks

By 24 weeks post-ACLR, the quadriceps should be capable of handling high-load resistance training (>85% 1-RM), signaling the transition from traditional strength into eccentric- and power-based programming.

For athletes returning to high-demand sports (Level 1: cutting, pivoting, jumping), rehab now must replicate the force profiles, movement speeds, and neuromuscular demands seen in competition.

Patellofemoral forces during cutting/pivoting can reach 13–18x bodyweight, so training needs to match that stress tolerance.

For reference:

• A deep squat (to ~120° flexion) at ≥85% 1-RM can replicate these forces.

• A maximal isometric OKC extension at 90° flexion only produces ~7–8x BW patellofemoral load.

This evidence strongly favors CKC resistance training in deep flexion angles (>120°), and/or eccentric training above 100% concentric 1-RM to simulate sport-specific forces and prepare tissue tolerance accordingly.

Eccentric-Specific Quadriceps Training

This is where eccentric overload becomes key.

This is how to program it:

• Use double-limb concentric → single-limb eccentric technique:

  • Both limbs extend the load (concentric phase).

  • Surgical limb alone resists the return (eccentric phase).

• CKC: Perform from 0–110+° of flexion.

• OKC: Focus between 45–100+° of flexion.

These contractions enhance tendon stiffness, muscle strength, and deceleration capacity, and should be integrated with progressive change-of-direction and deceleration drills — mimicking the quadriceps' role in absorbing force during sport-specific movements.

Power and Velocity-Based Quadriceps Training

This phase should also focus on rate of force development (RFD) — an area often impaired long-term post-ACLR, especially with BPTB or QT autografts.

• Velocity-based training (VBT):

  • Best executed using barbells with linear position transducers or jump training machines.

  • Each rep should be performed with maximal intent.

  • Stop working sets when velocity drops >10% from peak output to prioritise explosive effort.

• Ballistic/Plyometric Integration:

  • Pair VBT with plyometrics (e.g., loaded jumps, hops, bounds) to target the stretch-shortening cycle and neuromuscular reactivity.

  • This hybrid approach improves motor control, reactive strength, and reinjury resilience.

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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