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Recommendations for Hamstring Function Recovery After ACL Reconstruction

Buckthorpe, M., Danelon, F., La Rosa, G., Nanni, G., Stride, M. and Della Villa, F., 2021. Recommendations for hamstring function recovery after ACL reconstruction. Sports Medicine, 51(4), pp.607-624

In today’s letter

• Overview of the how to rehab hamstrings after an ACL reconstruction

• 3 clinical tips

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

• 3 resources to check out to further your knowledge about …

• The funny side: Aha, aha, yes we store the equipment up there 😄 

• Rapid Results =

Hamstring strength deficits are one of the most significant risk factors for ACL re-injury. Standard return-to-sport testing often overlooks hamstring function, which is why we need to start giving the hamstrings more love!

• Professional takeaway =

Prioritise eccentric hamstring strength testing and training, as it contributes heavily in stabilising the knee during high-speed running and deceleration. Aim for ≥90% limb symmetry index (LSI) when strength testing and make sure hamstring strength is at least 60% of quadriceps strength to reduce re-injury risk before allowing to return to sport.

4 Phase Tendon Rehab Framework

Core Principles of Hamstring Rehab After ACLR

Let me just give the silver lining from the get go,

A well-rounded, strategic approach that supports long-term recovery and performance is going to be the bread and butter of any rehab plan, but especially the hamstring group after ACLR.

We need to consider neural, morphological, and mechanical factors — like muscle activation, tendon health, and force production — because they all contribute in how well the hamstrings recover and function.

Yes strength is importnat, but its not as black and white as this, how well the muscles coordinate with the rest of the body is evenly (if not more) as importnat.

One of the most important principles is criterion-based progression.

This means we don’t just move on to the next phase because a certain amount of time has passed — we advance only when specific functional goals are met.

For example, Early on, we focus on reducing swelling, restoring range of motion (ROM), and hitting strength benchmarks, making sure we build on a solid foundation without rushing the hamstring.

Each stage of ACL rehab has distinct hamstring goals.

• Pre-op focuses on reducing pain and swelling while maintaining neural activation.

• Early-stage rehab (0–6 weeks post-op) protects the graft and minimises muscle atrophy with low-load isometrics.

• By mid-stage (6–12 weeks), we work on neuromuscular control and functional strength with moderate-load exercises.

• Late-stage (3–6 months) introduces high-load eccentric training and plyometrics,

• Return-to-sport (6+ months) emphasises high-velocity movements and sport-specific drills.

Exercise selection and progression follow a functional task hierarchy. We start with weight-bearing exercises like step-ups and squats, move to high-load control with landing mechanics and jump training, and finally integrate sport-specific agility and sprinting. Monitoring joint loading, muscle activation, and rate of force production ensures proper adaptation at every stage.

For those with a hamstring graft, unique considerations apply. Early on, avoiding excessive hamstring stretching protects the healing graft.

In mid and late phases, eccentric loading rebuilds tendon integrity, and addressing compensatory patterns like quad over reliance ensures balanced strength and proper mechanics

All right, with principles out of the way lets looks at the stages in more detail

Early-Stage (0–6 Weeks Post-Op)

Early-stage rehab lays the foundations for recovery.

At this “fragile” period care and protection should be at the front of our minds (especially with a hamstring graft).

The main goals are:

1. Reducing pain and swelling

2. Restoring knee range of motion)

3. Helping patients return to daily activities like walking without crutches

4. Minimising muscle atrophy in the hamstrings and quadriceps is also important, as strength loss happens quickly without adequate stimulation.

If your patient opted in for the hamstring graft, caution is critical.

The donor site needs 6–8 weeks to heal, so high-intensity strengthening off-limits. Instead, gentle, low-intensity exercises activate the hamstrings without straining the healing tissue.

Isometric and concentric movements at short-to-medium muscle lengths are the safest options.

Simple but effective exercises work best early on.

• Prone heel squeezes and supine knee presses maintain activation without overloading the graft.

• For concentric work, seated hamstring curls with low-resistance bands and controlled bridging variations engage the hamstrings and glutes safely.

• Functional movements like heel slides and partial weight-bearing movement like mini-squats and step-ups, restore ROM and integrate hamstring activation into daily movement.

Avoiding common pitfalls is just as important.

• High-load or eccentric exercises can delay healing, and aggressive hamstring stretching stresses the donor site.

• Premature progression without pain-free movement and good ROM can also set the patient back.

Mid-stage rehab should only begin once key milestones are met:

1. Minimal pain and swelling

2. Full knee extension and functional flexion

3. Walking without crutches

4. Good quadriceps control.

Mid-Stage (6–12 Weeks Post-Op)

In mid-stage rehab the focus shifts from basic recovery to rebuilding strength, refining movement, and improving overall fitness.

A major goal is resolving muscle strength imbalances, particularly in the hamstrings, which often show a 50% deficit at this stage.

We aim to close that gap, targeting knee flexor strength within 20% of the unaffected limb (80% LSI). During this phase, we also restore motor control through weight-bearing exercises and light jogging on treadmill, while rebuilding muscle volume, endurance, and work capacity.

This stage is split into two halves, each with different goals.

1. In the first half, we focus on restoring muscle volume and work capacity with low-to-moderate loads. Blood flow restriction training can be introduced.

2. In the second half, the goal moves to muscle volume and further reducing strength deficits. This involves moderate-load, isolated exercises like partial-range Nordic hamstring curls and hamstring slider curls, as well as functional movements like squats, lunges, step-ups, and light-to-moderate deadlifts. Running is reintroduced, starting with treadmill jogging to focus on gait and symmetry.

Throughout mid-stage rehab, progression is guided by key principles:

• Progressive overload

• Motor control

• Balanced mix of knee- and hip-dominant exercises to improve overall lower limb strength.

Progression depends on clinical experience and improvements in strength, movement quality, and load tolerance.

Before moving to late-stage rehab, patients should achieve knee flexor strength within 20% of the unaffected limb and demonstrate good movement patterns in squatting and jogging.

Late-Stage Hamstring Rehab and Return-to-Sport

Late-stage rehab and return-to-sport training focuses on preparing the athlete/patient for sport-specific demands.

The main goals are to restore hamstring function, maximise force development, and reduce re-injury risk.

Full restoration of knee flexor and hip extensor strength (both actions of the hammy) is a non negotiable, with an emphasis on speed, control, and rate of force development.

This stage includes a few progressive elements.

1. High-load isolated strengthening, with exercises like Nordic hamstring curls and heavy hamstring curls, builds strength, especially at long muscle lengths.

2. Functional strength integrates power into sport-specific movements such as Romanian deadlifts and single-leg squats.

3. Motor pattern re-training refines movement quality through agility drills, change-of-direction tasks, and stop-and-go exercises.

On-field reconditioning in a sport-like settings is going to have a good mental benefit, progressing from controlled drills to full-intensity small-sided games.

Sprinting is very importnat for restoring eccentric strength & rate of force development gradually progressing from submaximal to full-speed.

Sport-specific training helps skills transfer into performance (focusing on eccentric strength predominantly to challenge the hamstrings at vulnerable lengths)

By the return-to-sport phase, athletes should achieve knee flexor and hip extensor strength within 10% of the unaffected limb and demonstrate symmetrical movement patterns in sport specific drills.

Psychological readiness should not be overlooked either. The athlete must feel confident in performing at pre-injury levels.

Return-to-Sport Testing After ACLR

Hamstring deficits are a risk factor for re-injury, but most RTS protocols focus on timelines, hop tests, knee function, and quadriceps strength (which is good, but not perfect).

What should we measure the?

First, clear strength benchmarks are needed.

The Limb Symmetry Index should target ≥90% for knee flexor strength compared to the contralateral limb. The knee extensor/flexor ratio should be ≥60%, making sure that the hamstrings support the quadriceps.

Absolute strength is also important, with knee flexor peak torque ≥1.5 Nm/kg and eccentric peak torque ≥2.5 Nm/kg. Given the hamstrings' role during high-speed and deceleration, eccentric strength is vital. Tools like the NordBord can assess both strength and symmetry.

Goals = >90% LSI and >350 N of peak torque.

Looking beyond strength, functional performance indicates how well the muscles translate to sport-specific moves.

Sprinting is the main marker, as it activates the hamstrings significantly. Athletes should reach their pre-injury or sport-specific peak speeds during rehab, tracked with GPS or speed gates. Rate of force development (RFD) is another metric of explosive strength, however, to test that clinically without a budget is not easy.

3 Clinical Tips

1. Hamstring Strength in RTS Decisions:
   Don’t rely solely on time-based protocols or quadriceps only testing — hamstring deficits are a major risk factor for ACL re-injury. Assess both absolute hamstring strength and limb symmetry, aiming for ≥90% LSI and 60% of extensor to flexor ratios (for example if Quads produce 100N of force then hamstring should produce 60N)

   You can use an affordable hand held dynometer for the above

2. Eccentric Hamstring Strength:
   Eccentric strength at long muscle lengths protects the ACL during high-speed running and deceleration. Include exercises like Nordic hamstring curls when the time is right and if you’re one of the lucky ones who has the ability to use an isokinetic machine then assessing eccentric peak torque (≥2.5 Nm/kg) to gauge readiness for sport-specific demands is going to get you to gold standard as close as possible.

3. Functional and Sport-Specific Testing:
   Running speed and change-of-direction ability reflect real-world hamstring function in sport. Use GPS data or speed gates (if you can 😄) to monitor peak sprinting speeds

The Funny side:

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

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