Return to Sport After Injury — Criteria, Not the Calendar

What decides it: Criteria, not a date
After ACL surgery: Not advised before 9 months
Also tested: Psychological readiness

The calendar is not a criterion

The most-quoted number comes from Grindem and colleagues: for every month return to sport was delayed, up to nine months after ACL reconstruction, the reinjury rate dropped by around 51%. Another study found young athletes who went back before nine months sustained new injuries at seven times the rate of those who waited.

But the ninth month is not a magic number. In the same research, those who failed the return-to-sport criteria had a second knee injury in 38.2% of cases, against 5.6% for those who passed. The groups were small, so that gap did not reach statistical significance — but it points the same way as the rest of the evidence. So what protects you is not the date, but what you can do by that date.

The same logic applies to injuries that are not the ACL, though the timescales are far shorter. A torn calf, a pulled hamstring, a sprained ankle — each has capability criteria that make more sense than counting weeks.

What gets tested — and why the numbers are not enough

The usual test battery compares the injured side against the healthy one: quadriceps and hamstring strength plus four single-leg hop tests. The commonly used threshold is 90% of the healthy side. The numbers do mean something — in Grindem's work the relationship is continuous: each 1 percentage point of quadriceps strength symmetry gained lowered the reinjury rate by about 3%, with no magic cut-off at 90. Among professional footballers, those who had not met the criteria for full recovery had four times the risk of ACL graft rupture.

Now the part that rarely gets said. That 90% threshold has turned out to have poor predictive value for a second ACL injury, and it can mislead. The reason is simple and easy to miss: after months without full training, the healthy side has weakened too. One review found that 34% of athletes who reached 90% symmetry at six months had not reached 90% of their own pre-injury capacity.

So we do not stop at left-versus-right. If there is any record of what you could do before the injury, that is a far more honest comparison. If there is not, we use age- and sport-appropriate benchmarks, and we test under fatigue — because injuries rarely happen on the first repetition.

The most skipped part: psychological readiness

There is a questionnaire for exactly this, called the ACL-RSI, measuring three things: emotions (fear of reinjury, confidence in the knee, anxiety), confidence in performance, and how you appraise risk. Scores above roughly 65 are associated with returning to the same sport at two-year follow-up.

Here is why it matters: in a systematic review this psychological readiness scale was the strongest predictor of successful return to sport — and functional tests alone did not predict it. Which means someone can pass every hop test and still not go back, or go back but play guarded, which carries its own risk.

If you feel afraid, that is not weakness and not something to hide from your therapist. It is information. We treat it like any other finding: gradually, with controlled exposure to the movements you have been avoiding, until the knee feels like something you can trust again.

What to bring

Operation notes or a letter from your surgeon, including any restrictions given
Previous return-to-sport test results, if you have had any
Your sport and position — the movement demands differ enormously
Your training and match schedule, so the program is realistic
The shoes and protective gear you actually compete in
Any record of your pre-injury capacity — running times, lifting numbers, anything

Frequently asked questions

My doctor cleared me but I am still afraid. Is that normal?

Very normal, and good practice actually measures it. The psychological readiness scale used after ACL injury turns out to predict successful return better than the physical tests do. Fear that goes unaddressed tends to end one of two ways: not going back at all, or going back and playing guarded — and playing guarded carries its own risk. We work on it gradually rather than telling you to "just trust it".

Both legs are equally strong now. Does that mean I am ready?

That is good news, but not necessarily enough. After months without full training the healthy side has weakened too — so "equally strong" can mean equally reduced. One review found 34% of athletes who reached 90% symmetry had not reached 90% of their own pre-injury capacity. That is why we also compare against age- and sport-appropriate benchmarks, and test you when you are tired.

My injury was not an ACL. Do I still need this kind of testing?

The principle is the same, the scale is different. Most of the research is in ACL because the stakes are high and recovery is long, but the logic generalises: make sure capacity is back before the load is, test under fatigue, and build up gradually. For a muscle or ankle injury the timescale is weeks rather than months and the tests are simpler — but it is still criteria, not a date.

Sources

The figures and recommendations on this page come from the sources below. The links go to third-party sites.

This page is educational and does not replace an examination by a doctor. If your child is unwell, or something does not feel right to you, have them seen first.