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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

• Meme of the week: Its just not something I do every day 😄 

• Rapid Results =

A successful hamstring rehab program after ACL reconstruction incorporates both knee and hip dominant exercises. This approach helps avoid compensatory movement patterns that could overload the knee and compromise recovery

• Professional takeaway =

In the early stages of rehab (0-8 weeks), focus on low-load, hip-dominant exercises like glute bridges and hip thrusts to protect the graft and promote neuromuscular activation. As the patient progresses (8-16 weeks), gradually introduce knee-dominant exercises like leg curls and slider hamstring curls to target knee flexor strength while maintaining emphasis on hip work

Did you know?

When it comes to hamstring rehab after ACL reconstruction (ACLR), there’s a surprising lack of specific research focused protacols on how to help recover hamstring function in these patients.

Most of what we know about hamstring training comes from research on hamstring strain injury — which is helpful, but not entirely specific to the different challenges ACLR patients see.

Since we don’t have much evidence directly addressing this, it makes sense to take what we’ve already learned about hamstring rehab and thoughtfully apply it to the ACLR population.

The key word here is “thoughtfully”

Effective recovery of hamstring strength after ACLR really comes down to three things:

1. Knowing how to properly train the hamstrings

2. Understanding the specific deficits that follow after ACLR

3. Building the rehab approach around the body’s adaptive strategy, and being mindful of the entire ACLR recovery phase so that training can be directly and appropriately applied.

Section 2 of the study (the focus of todays breakdown) by Buckthorpe & colleugues looks into the specific deficits that follow ACLR, and gives practical tips on how to actually train the hamstrings in a way that not only follows solid training principles but also adapts those principles to fit the specific needs of patients after an ACL surgery.

Eventually, this will lead into more detailed recommendations for every stage of functional recovery, along with clear progression criteria (the 3rd and final breakdown on hamstring training after ACL recon — which will be sent next week)

Let’s boogie!

Optimal Loading…

Optimal loading is absolutely the main bit to get right, especially early on.

In a nutshell,

That means applying just the right amount of stress to the muscles so they adapt and get stronger — building neural, mechanical, and structural changes — without pushing too hard and interfering with the body’s natural healing process.

The tricky part?

There’s no one-size-fits-all training program. But we all know that by now…

A lot of the current advice is based on studies of people who aren’t injured, which doesn’t always translate perfectly to post-ACLR rehab. That’s why it’s important to understand factors of adaptation and respecting the healing timeline.

So, what kind of changes are we aiming for in rehab?

On the mechanical side, we want to build adaptations like:

• Maximal strength

• Rate of force development (RFD)

• Muscle endurance

And heavy resistance training is going to fit in well, especially for improving eccentric strength.

In terms of neural improvements, we want:

• Better coordination between muscles

• More efficient motor unit recruitment

• Faster firing frequency

Which all respond best to high-intensity training.

Finally, the morphological changes (muscle structural changes)

• Muscle growth

• Changes in muscle architecture

• Stronger tendons

For these adaptations, we need to apply enough training volume to drive hypertrophy.

To get the right mixture of the safe and THOUGHTFUL rehab protocols understanding a few basic training principles is essential.

The Training Principles

Load is the most important factor in resistance training. Patients can start seeing strength gains at lower intensities (around 40–60% of voluntary activation), but if you want those bigger neural adaptations and more significant strength improvements, higher intensities are where it’s at.

Volume, on the other hand, is more important for muscle growth than for building raw strength or altering muscle architecture.

For patients after an ACL reconstruction, the timing of hamstring loading also depends on the type of surgery they’ve had.

If they’ve had a hamstring graft, it’s generally best to wait 6–8 weeks before starting hamstring strengthening to allow the tissue to heal properly.

That said, lower-intensity exercises can often start earlier, and the loading process should happen in stages.

1. Early rehab focuses on muscle endurance and hypertrophy with lower-intensity work

2. The mid-stage ramps up both intensity and volume

3. The late stage builds up to maximal strength and neuromuscular activation with heavier weights and moderate volume.

As patients get closer to returning to sport, the focus shifts again — this time to explosive strength and power.

I’m talking very high intensity and low volume, for examples sets of fewer than five reps.

Equipment like blood flow restriction (BFR) can also be really useful early on, especially when pain or muscle inhibition limits how much load you can use.

Throughout the entire process, periodisation — that is, carefully adjusting load, sets, and reps over time — helps maximise gains while still giving tissues the time they need to heal.

By the final stages of rehab, the goal is to make sure athletes have the explosive strength and power they’ll need to safely and confidently return to their sport.

The Phases Summarised

1. Early Phase: Low intensity, focus on endurance and hypertrophy.

2. Mid Phase: Moderate intensity and volume for hypertrophy.

3. Late Phase: High intensity for maximal strength and power.

Eccentric Strengthening

Eccentric training can help in many ways — and to understand why, we need to take a look at how the hamstrings work.

During running and decelerating, the hamstrings act eccentrically—they lengthen under tension—to resist anterior tibial translation and control knee extension.

These moments (especially when intense & in fatigue) are exactly when the risk of injury skyrockets.

The issue is,

That for patients who’ve had a hamstring graft, the ability of the hamstrings to produce eccentric force often takes a serious hit. Studies show they can have a 16–20% deficit in eccentric knee flexor strength—which isn’t always fixed with standard rehab.

Even after going through a typical program, a lot of patients still have lingering issues with muscle fascicle length and neuromuscular activation. That’s a big deal because those deficits can limit performance and increase the risk of reinjury.

So why is eccentric training so effective?

Adaptation!

Over just 6–10 weeks, it can increase eccentric knee flexor strength by 13–19%.

Even more impressive, it’s one of the best ways to increase the fascicle length of the biceps femoris long head —with studies showing gains of 16–34% in just 6–8 weeks.

That’s important because longer fascicles help muscles absorb more energy and tolerate stretch better, which means fewer injuries.

Eccentric work also shifts the torque curve, increasing strength at longer muscle lengths—something concentric training just doesn’t do.

In fact, one study showed concentric-only training can actually shorten muscle fascicles, which is the opposite of what you want.

One of the biggest challenges post-ACLR—for both the quad and hamstring graft— is arthrogenic muscle inhibition. Pain and swelling after surgery interfere with neuromuscular activation, making it harder for the hamstrings to fire properly.

Eccentric training, combined with neuromuscular re-education and pain/ swelling management, can help overcome this roadblock.

Programming

In terms of programming, the timing of eccentric training is importnat.

In the early rehab phase (0–8 weeks post-ACLR), it’s smart to start with longer-length isometrics and light concentric exercises (prone leg curls at 90° knee flexion or supine bridges with a slow eccentric lower).

The exercises in these lengths help improve fascicle architecture and get neuromuscular activation going without overloading the healing tissue. Once the persons hit the 13-week mark and as long as the fundamental are covered (pain, swelling etc), it’s time to step things up.

Start introducing more demanding eccentric work like short fall Nordic hamstring curls or slider leg curls, gradually increasing load and volume.

By the time athletes are gearing up for a return to sport, the focus should shift to sport-specific eccentric demands—like sprint decelerations and cutting drills.

At this stage, it’s also importnat to integrate plyometrics and reactive training to make sure the hamstrings are ready for quick, explosive movements.

Hip + Knee Exercises = Good Rehab

Balance, balance, balance…

When rehabbing a hamstring after ACL reconstruction, especially with a hamstring graft, its fundamental to balance knee- and hip-focused exercises to restore function

The hamstrings have two main roles:

1. They help flex the knee, which is significant for ACL stability

2. They extend the hip, working alongside muscles like the glutes and adductors.

During sprinting, the demand on the hip muscles is about twice as high as on the knee. If these muscles are weak, the body may compensate by putting extra strain on the knee, increasing the risk of re-injury.

No bueno!

A solid rehab program should hit both of these functions by including knee-dominant exercises (like leg curls or Nordic hamstring curls) to target the semitendinosus and biceps femoris short head, as well as hip-dominant exercises (like Romanian deadlifts and 45° hip extensions) to work the semimembranosus and biceps femoris long head.

This helps develop the hamstrings evenly and prevents imbalances that could mess with knee control and raise injury risk.

In terms of patients with an ACLR hamstring graft, the plot thickens.

If the semitendinosus tendon doesn’t heal properly, focusing too much on knee-dominant exercises could overload the biceps femoris short head and disrupt knee stability.

To avoid this, early rehab (0-8 weeks post-surgery) should emphasise low-load, hip-focused exercises like glute bridges and hip thrusts, which protect the graft while building hip strength and neuromuscular control.

As rehab progresses (8-16 weeks), you can add moderate-load knee-dominant exercises like prone leg curls and slider hamstring curls to increase knee flexor strength while still focusing on hip work.

By the later stages (16+ weeks), high-load, sport-specific movements like Nordic hamstring exercises and stiff-leg deadlifts are key for building eccentric strength and getting the body ready for more intense activity.

Making simple adjustments, like changing foot rotation, can also help target specific parts of the hamstrings.

• Internal rotation works the medial hamstrings (semimembranosus/semitendinosus)

• External rotation hits the lateral hamstrings (biceps femoris long head and short head).

3 Clinical Tips

• Eccentric and Long-Length Hamstring Training
  In the later stages of ACLR rehab, focus on eccentric exercises like Nordic hamstring curls and Romanian deadlifts to improve fascicle length, which enhances energy absorption and reduces hamstring strain injury risk.

  In early phases, if pain or arthrogenic muscle inhibition limits intensity, consider using blood flow restriction (BFR) training with lighter loads to maintain strength development without overloading healing tissues.

  2.Isolated and Functional Strength Work
  Combine isolated exercises (like seated hamstring curls) to build foundational muscle strength with functional drills (like single-leg deadlifts and deceleration drills) to improve intermuscular coordination and sport-specific movement quality.

  3. Focus on Neuromuscular Control and RFD
  Incorporate biofeedback tools (like EMG) during landing and cutting drills to emphasise medial hamstring engagement, which is essential for controlling dynamic knee valgus. As the athlete progresses, prioritise rapid force development (RFD) through reactive and ballistic exercises like resisted sprints and drop jumps, preparing them for the high-speed demands of sport.

Meme of The Week

When You’re Ready to Learn More

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

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