Assessing ACL Return to Sport Readiness: Expert Criteria

There’s a point in ACL rehab where things get a bit uncomfortable.

It’s no longer about swelling, range, or even basic strength. The athlete is running, lifting well, ticking off the usual milestones. From the outside, everything looks on track. But internally, you start asking a different question: are they actually ready?

Because this is the stage where decisions carry real weight. Return them too early, and the consequences can be significant. Hold them back unnecessarily and you impact performance, confidence, and career progression.

The tricky part is that most athletes at this stage don’t look obviously unready. You have to know where to look. While return-to-sport decisions should consider both physical and non-physical factors, this blog focuses on some of the key movement-based criteria expert physio Dr Tim McGrath uses to assess his athletes.

If you want to see exactly how an expert physio approaches this stage, watch Dr Tim McGrath’s full Case Study HERE. With Case Studies you can step inside the minds of experts and apply their strategies to get better results with your patients. Learn more here.

The case

A 23-year-old elite footballer, eight months post ACL reconstruction using a hamstring autograft. No additional pathology.

He’s progressed well through rehab. Strength is improving, he’s back running, and he’s moving into more advanced, sport-specific work. At a glance, you’d feel pretty comfortable with where he’s at.

But when Tim applies more detailed, evidence-based testing, a few deficits start to emerge.

What should you consider

Tim introduces this stage of rehab with a really useful analogy. Watch him explain in this clip from his Case Study:

At this stage, there are a few key things worth paying closer attention to. Not as a rigid checklist, but as a way to guide what you’re looking for to ensure a thorough assessment of return to sport readiness.

Obviously, you’re still interested in the fundamentals: do they have enough mobility, and can they control it? Is their strength where it needs to be, particularly through the quads? See Tim describe how he assesses quadriceps function in this snippet from his Case Study:

But beyond that, you need to look at factors that may contribute to re-injury risk. Because it’s not just about getting the athlete back at peak performance, you really want to keep them there by reducing their risk of re-injury.

A few things are worth considering. First, how much knee flexion are they using when their foot hits the ground? Do they move through range to absorb load, or stay relatively stiff? And what does that look like when you increase the demands, such as changing direction or dual tasking?

This is where measures like knee flexion at initial contact, and net knee flexion from initial contact to peak knee flexion, become useful data. They give you something objective to track, rather than relying purely on visual judgement.

You also start to look more closely at how the athlete organises themselves around the knee. Where is the foot landing relative to the centre of mass? What’s happening with rotation through the limb? How are they managing speed and angle when they cut?

Tim describes the “pepper grinder” effect, where the foot remains more externally rotated at contact, then rapidly transitions as the athlete changes direction. That combination can introduce rotational stress through the knee, particularly under speed.

These are the kinds of details that don’t always show up in standard testing, but become really valuable when you’re deciding whether someone is ready to return to sport.

What was found in this case

When Tim takes a closer look at this athlete, a few consistent patterns emerge.

There’s reduced knee flexion at the moment of foot contact across multiple tasks. Running, landing, and change of direction all show a similar tendency, the athlete is relatively stiff on initial contact, rather than bending into the movement.

From there, the total amount of knee flexion achieved through the movement is also limited. He’s not really moving through that range to absorb load, which means more of the stress is being transferred elsewhere.

There’s also a clear rotational component. The foot position at contact, combined with the way the limb rotates, creates that “pepper grinder” effect, introducing rotational stress through the knee, particularly during cutting.

None of these findings are dramatic in isolation. But together, they highlight a pattern that could increase re-injury risk if left unaddressed.

Addressing deficits

One key concept is how important it is to bring the athlete into the process.

If you’re trying to change something like knee flexion in a cutting task, the athlete needs to understand what they’re trying to achieve. Otherwise, it just becomes another drill with no real carryover.

Tim also highlights that these changes take time. You’re looking at roughly 4–8 weeks to see meaningful improvement. And if things haven’t shifted by then, it’s a sign to reassess. Either the athlete hasn’t fully understood the goal, or the intervention itself isn’t targeting the problem effectively. See how Tim would address his athlete’s deficits in this video from his Case Study:

Wrapping up

End-stage ACL rehab is where things become less clear-cut.

Athletes often look “good” at this stage. They’re strong, they’re moving, and they’re progressing. But it’s these more subtle movement patterns that can make the difference.

Return to sport isn’t a single decision point, it’s a process of building capacity and refining how that capacity is used.

Having clear, data-informed guidance can make this stage far more manageable.

If you want to see exactly how an expert approaches these late-stage decisions, watch Dr Tim McGrath’s full Case Study here.