Part of ACL reconstruction rehab
ACL return to sport testing: what it is and what you have to pass
Warning signs, and when to get help
What is ACL return to sport testing, and who does it?
A physiotherapist or physical therapist runs it, usually in one appointment with equipment, and the output is a set of numbers, not a yes or a no. The operated leg is measured against the other leg, and sometimes against what your sport demands, on strength, jumping, landing, running and how you feel about the knee.
The equipment is the part most people do not expect. Thigh strength is measured on a machine, either an isokinetic dynamometer or a fixed handheld one, because a leg press and a feeling cannot tell you accurately how far apart the two legs are. Hop and jump tests are measured with a tape, a timing gate or a force plate. Confidence is measured with a questionnaire rather than a conversation, because the questionnaires have been studied and the conversation has not.
That is also why this page cannot hand you a self-test. A single hop in the garden tells you almost nothing about whether the knee is ready, and the numbers below are not pass marks you can award yourself. What you can do is ask your clinic which battery they use, ask for your own results, and ask which item is furthest off.
Where this sits in the program: it comes after stage 4 of the ACL reconstruction rehab program, and after running, which has its own shorter list of criteria in ACL return to running. Running is the better studied of the two for timing and the less studied for criteria: a scoping review of 201 studies found the time-based criteria for a first run clustered at a median of 12 weeks with a range from 5 to 39 weeks, and fewer than one in five of those studies added any clinical, strength or performance criterion at all (Rambaud and colleagues, 2018). Return to sport is the opposite problem, with criteria proposed and the timing argued over.
What do you have to pass?
Four kinds of thing, and your clinic decides the exact mix. The guideline that sets it out most clearly also says there is no evidence on which progression or discharge criteria should be used, which matters before you treat any single number as the gate (Kotsifaki and colleagues, 2023).
The Aspetar guideline gives one list, not a tier for amateurs and a tier for professionals, and whose list it is matters. The guideline proposes it as the minimum for clearing a professional athlete from the clinic or hospital to start training with their club, and it says the criteria can be adjusted and individualised to the person's previous activity level. The list: no pain or swelling, full knee movement, a stable knee on examination, normalised patient-reported function and psychological readiness measured with questionnaires including the IKDC, the ACL return to sport after injury scale and the Tampa Scale of Kinesiophobia, 100% quadriceps and hamstring symmetry on isokinetic testing at 60 degrees per second for a return to high demand pivoting sport, with preoperative absolute values restored as a minimum where they are available along with normative values for the sport and level of play, over 90% symmetry of jump height and of concentric and eccentric impulse on countermovement and drop jumps, a reactive strength index above 1.3 on two legs and 0.5 on one leg for field sport athletes and higher for track and field, jumping mechanics normalised for moments, angles and work, over 90% symmetry of vertical ground reaction forces and knee mechanics during high-speed running and change of direction, and a completed sport-specific training program.
If you play recreationally, that list is not your pass mark. It was written for a professional going back to a club program. What a clinic is likely to ask of you comes further down.
One item on that list is easy to skim past and matters to everybody: restoring absolute values, not just symmetry. Symmetry is a ratio, and a ratio can be met by the other leg getting weaker as well as by the operated leg getting stronger. The same guideline says in its own recommendations that the uninvolved limb's strength should be monitored and restored to baseline or optimal levels too, which is the clinical answer to that problem.
Passing this list is also not the same as playing. The guideline is explicit that completing rehabilitation and being cleared to return to sport is not the same as returning to competition, and that a transition phase of progressive, controlled exposure to the demands of the sport belongs between the two. So the numbers above buy a return to training, not a return to match day.
There is one more thing to know about where that list came from. The guideline says its own discharge criteria rest on the group's clinical experience, research findings and their own normative data rather than on a trial. So a clinic treating a recreational athlete will often use a different battery and lower thresholds, and that is not a corner being cut. Surgeons and clinics genuinely differ here, and where your own team's thresholds or timings differ from anything on this page, theirs are the ones that count. They know your graft, whatever else was repaired in the same operation, and how your knee has behaved since.
The van Melick guideline, written for the Royal Dutch Society for Physical Therapy, asks for the same four domains in a battery of strength, hop, movement quality and psychological tests, used to decide when somebody progresses, with rehab carrying on for 9 to 12 months after surgery (van Melick and colleagues, 2016).
The hop side of it is usually three to six tasks, not one, because a single hop is easy to compensate on. The single leg hop and hold, single leg hops over a line, skater hops and the drop landing are the shapes most batteries use, and they are worth practicing before the test instead of meeting them cold, in the stage your physio opens rather than on your own. Before you follow any of those four links, read the next two paragraphs: one is a date set by your graft, and the other is the list of people who have to ask first.
After a hamstring graft or a quadriceps tendon graft that date is later again, at least 16 weeks after surgery unless your surgeon or physio has cleared it earlier, because the place the tendon was taken from is still rebuilding (Briem and colleagues, 2026).
Jumping and hopping also load the joints, the bones and the pelvic floor. If you have osteoporosis or have had a fall in the past year, ask your physio before you do any hopping. If you have had a hip or knee replacement, get the go-ahead from your surgeon before you try hopping. Many surgeons advise against jumping and hopping after a joint replacement for good, not just for the first months, because each landing sends high impact through the new joint. If you are pregnant, have had a baby in the past year, or leak urine when you jump, cough or sneeze, check with your midwife or physio before you start this stage. Stop the hopping and speak to your physio if urine leaks while you are doing it, or if you feel pressure or heaviness low in your pelvis. After having a baby, postnatal guidance usually leaves jumping and hopping until at least 3 months after the birth, once a pelvic floor check shows you are ready. With a heart condition or high blood pressure, check with your doctor before you start.
This page is for adults. A child or teenager who has had ACL surgery should follow the plan from their surgeon and physio, and ask them before trying any exercise on this page.
The questionnaires your clinic may use are covered in outcome measures in physical therapy, the lower extremity functional scale and the patient specific functional scale.
Why strength is tested separately from hopping
Because you can pass a hop test on a knee that is still weak, and the hop test will not tell you.
This has been measured directly. In 26 male athletes who had been cleared to return to sport after an ACL reconstruction, tested within two weeks of that clearance at about nine and a half months after surgery and compared with 23 uninjured male athletes, hop distance on a single leg hop for distance came out at 97% of the other leg, give or take 4%. The work done by the operated knee during the push off was 69% of the other side. The athletes were making the distance up elsewhere, with more hip work, more hip bend, more pelvic tilt and more forward lean during landing, and the authors concluded that how far somebody hops tells you little about the knee itself, because the number mostly reports what the hip and the ankle did (Kotsifaki and colleagues, 2022).
There is a simple reason it can hide so much, and it comes from a different study by the same group. In 20 healthy, physically active people, 87% of the distance in a single leg horizontal hop was down to the hip and the ankle, 44% and 43% of it, which leaves the knee about an eighth of the job (Kotsifaki and colleagues, 2021). So a knee well short of its old self can be carried to a near symmetrical number by the two joints either side of it.
That is the finding to carry into your own test. A 97% hop symmetry can sit on top of a knee doing just over two thirds of its share. The body is good at hiding a weak knee, and it hides it by using the hip.
What that study cannot tell you is whether the same figures hold for a woman, a recreational player or an older knee. All 49 participants were men aged 18 to 35 playing at a high level, recruited at one hospital, and the authors say their results should be applied to women and other groups with caution. The lesson about hop distance holds; the exact percentages belong to that group.
So strength gets its own measurement, on a machine, and hopping gets measured for how it is done as well as how far it goes. If your clinic can film your landings or use a force plate, that is why. And if your battery is hop distance alone, it is fair to ask what else they can measure.
When is the earliest you can go back?
Later than most people want, and the clearest numbers come from one cohort rather than from a guideline.
In the Delaware-Oslo study of 106 people who played pivoting sports and had an ACL reconstruction, going back to that level of sport carried a reinjury rate more than four times higher than staying below it, the rate of injuring the knee again fell by about half for each month the return was delayed up to 9 months after surgery, and no further drop was seen after 9 months. People whose thigh strength was closer to the other leg before they went back also had fewer reinjuries (Grindem and colleagues, 2016).
That study is where the 9 month position comes from, and it is worth being clear about its size. It is one cohort of 106 people playing pivoting sports, not a trial, and it does not promise anything to a reader whose sport, age or knee is different. It does fit the van Melick advice that rehab carries on for 9 to 12 months, and OrthoInfo describes most people being allowed back to full sport within 6 to 12 months depending on their progress, strength and movement.
Those two halves go together: time without the testing is a guess, and passing the testing at 5 months does not buy back the months. There is a surgical reason for the second half. A graft is not a ligament on the day it goes in, it has to be taken over by your own tissue, and the Aspetar guideline is explicit that criteria are used to progress rehab while respecting minimum time requirements for graft protection and healing. Good numbers do not speed that part up, which is why a clinic that tests you early usually retests rather than clears you.
How the risk looks once you are back, and what lowers it, is covered in preventing a second ACL injury. Returning to a specific sport brings its own demands, and returning to pickleball after an injury and return to sport after a meniscus tear cover two of them.
What happens if you do not pass
You get told which item failed, and that becomes the next block of work. It is common not to pass everything first time, and the usual pattern is strength, single leg landing control, or confidence.
A failed strength test means loaded single leg work for weeks to months, and your physio will set the dose. A failed landing test means landing practice, not more strength. A low psychological readiness score means the fear is being treated as a real finding, which it is: the Aspetar guideline notes that fear of injuring the knee again is the biggest reason people do not return to sport, so tell your physio if you feel nervous about it.
Ask for two things at that appointment. A retest date, so the failure has an end. And the one or two exercises that will move the failed item, rather than a longer program nobody follows. Graft type can change which item lags, and hamstring compared with patellar tendon graft covers that.
What testing cannot tell you
It cannot tell you that you are safe, and passing it has never been shown to keep a knee intact.
The honest state of the evidence is that the batteries are not fully proven. The Aspetar guideline says these criteria are yet to be fully validated, reviews it looked at came to different answers, and its own summary is that it is currently not clear whether passing a battery of tests is linked to a lower risk of a second ACL injury. The guideline adds the statistical reason: a second ACL injury is a rare event, and rare events are very hard to predict with any confidence. In the Grindem cohort, where passing meant scoring above 90 on quadriceps strength, hop tests and two self-reported function scales, 38.2% of those who failed went on to injure the knee again, against 5.6% of those who passed, and with those numbers the difference did not reach statistical significance (p=0.075). That is a hopeful signal rather than proof, and reporting it as proof would be the easy mistake.
If a meniscus or cartilage repair was done in the same operation, your surgeon owns when twisting, pivoting and impact are allowed, whatever your hop numbers say. And a knee that gives way, locks, pops or swells up within a few hours needs the same day route in the warning signs below, not a retest.
What testing does give you is the truth about where the leg is, which is more than a feeling or a month can offer. Take the numbers, train the worst one, and go back when the people measuring you say the leg is ready.
This page is general education and not a diagnosis or a personal clearance to play.
Related exercise programs
Warning signs
Get emergency help now
- Emergency: sudden, severe pain in your lower leg that is much worse than you would expect, especially with a tight bandage or brace on the leg. It may come with a tight, swollen leg, pain that gets worse when the muscle is stretched, numbness, pins and needles or weakness. Call emergency services or go to an emergency department straight away, and do not drive yourself. This can be acute compartment syndrome, which needs urgent surgery.
- Emergency: since your operation, you suddenly become short of breath, you get chest pain or pain in your upper back that may be worse when you breathe in, you cough up blood, your heart is beating very fast, or you faint. Call emergency services straight away, even if your leg looks normal. These can be signs of a blood clot in the lungs (pulmonary embolism).
Get help today
- Same day: a calf or thigh that is newly swollen or getting more swollen, warm, tender, red or darker than usual, has swollen veins that are sore to touch, or has a throbbing or cramping pain that does not fit your injury or condition, or that feels different from normal muscle soreness after exercise. This can be a sign of a blood clot (deep vein thrombosis), especially after surgery, an injury, time in a cast or boot, a long trip or a spell of being much less mobile than usual. Get medical advice the same day. If you are also short of breath or have chest pain, call emergency services.
- Same day: since your operation, your wound is oozing, leaking or has pus coming out of it, or its edges start to come apart, or your knee is tender, swollen, painful or red and it is not getting better or is getting worse, or you have a high temperature or feel hot and cold or shivery. Redness can be harder to see on brown or black skin. Contact your surgical team the same day, or get urgent medical advice if you cannot reach them. These can be signs of an infection in the wound or the knee joint. If you feel very unwell, go to an emergency department. If you have a very high or very low temperature, shivering you cannot control, you are breathing very fast or finding it hard to breathe, you are confused or your speech is slurred, your skin, lips or tongue look blue, gray, pale or blotchy (on brown or black skin this can be easier to see on the palms of the hands or soles of the feet), or you have a rash that does not fade when you press it, call emergency services, as this can be sepsis.
- Same day: your knee swells up quickly over a few hours and feels tight and full, with more pain than the day before, and there was no fall, twist or pop to explain it. This can happen while your temperature is normal and the wound looks fine. Contact your surgical team the same day, or get assessed the same day at urgent care or an emergency department if you cannot reach them. Bleeding into the joint and an early infection inside the joint can both look like this from the outside, and a knee that is hot to touch, or a temperature alongside it, makes an infection more likely. Do not wait for a call back if either is there. If you feel very unwell, go to an emergency department.
- Same day: your knee gives way, or you feel a pop, a shift or a twist inside it, and it swells up within a few hours or is very painful. Keep your weight off it and contact your surgical team, or get assessed the same day at urgent care or an emergency department. A fall or a twist can damage the new ligament (graft) or a meniscus repair. If the knee looks out of shape, or your foot turns numb, cold or pale, go to an emergency department straight away, and do not drive yourself. If the knee only feels a little unsteady now and then, with no swelling or pain, it is not an emergency, but tell your physio or surgeon in the next few days.
- Same day: the knee is locked, which means it is stuck bent and you cannot straighten it, even after gently trying to move it, or it suddenly will not bend or straighten as far as it did before. Contact your surgical team, or get assessed the same day at urgent care or an emergency department. A torn piece of meniscus can get caught in the joint and block it. This is different from the slow, gradual stiffness of the early weeks.
- Same day: you suddenly cannot straighten your knee by yourself or lift your leg straight when you could before, often after a pop, a fall or a stumble, or you notice a dip or a gap just above or below your kneecap. Keep your weight off it and contact your surgical team, or get assessed the same day at urgent care or an emergency department. After a patellar tendon or quadriceps tendon graft, the tendon or the kneecap near where the graft was taken can rarely tear or break.
- Same day: a leg or foot that is getting weaker, for example your foot drags, catches on the ground or slaps down when you walk (foot drop). Get medical advice the same day. If the weakness is getting worse by the hour, go to an emergency department.
- Same day: new numbness, tingling or burning in your lower leg or foot, beyond the numb patch of skin near your scars. Contact your surgical team or get medical advice the same day. If it started after a fall or an injury, or your foot or toes turn cold, pale, blue or gray, call emergency services or go to an emergency department straight away, and do not drive yourself.
Book an appointment
- Within a few days: your knee still will not straighten as far as the other one, or bend as far as your physio expects, and it is not improving from week to week, or it is slowly losing movement it had. This is not an emergency, but contact your physio or surgeon within the next few days. Tell them if the knee feels blocked right at the end of straightening, or clunks or hurts there, rather than simply feeling tight, and tell them if it stops short of straight in the months after your operation. A small lump of scar tissue at the front of the knee (a cyclops lesion) can block the last few degrees, and when it does it usually shows up 3 to 6 months after surgery. It is uncommon, most surgeons treat it first with rehab aimed at straightening, and a short keyhole operation to remove it is kept for a knee that stays stuck (D'Ambrosi and colleagues, 2026). Stretching harder is not the answer either way. Getting the knee fully straight is one of the first aims of rehab.
Common questions
What tests do I have to pass before going back to sport after ACL surgery?
Strength, jumping, running, knee stability and confidence, in some combination your own clinic decides. The Aspetar guideline gives one list, which it proposes as the minimum for clearing a professional athlete from the clinic to start training with their club, and it says the list can be adjusted to the person's previous activity level: no pain or swelling, full movement, a stable knee, normalised patient-reported function and psychological readiness on questionnaires, 100% quadriceps and hamstring symmetry on isokinetic testing at 60 degrees per second for a return to high demand pivoting sport, over 90% symmetry on countermovement and drop jumps, jumping and running mechanics brought back toward normal, and a completed sport-specific training program. Those criteria come from one group's clinical experience, research findings and their own normative data, not from a trial, and the same guideline states that there is no evidence on which progression or discharge criteria should be used. Clinics therefore use different batteries and often lower thresholds for a recreational player. Ask your physio which tests they use and what your last numbers were.
What does limb symmetry mean?
It is the operated leg expressed as a percentage of the other one, so 85% means the operated side produced 85% of what the other side did on the same test. It is used because it needs no normal values: you are the comparison. Two warnings come with it. The leg you are being compared against is not a fixed yardstick. It can lose strength across a long rehab, which flatters the percentage without the operated leg changing, and the Aspetar guideline answers that directly: it recommends that the uninvolved limb's strength is monitored and restored to baseline or optimal levels as well, and that absolute values are restored, preoperative ones where they exist plus normative values for the sport, rather than symmetry alone. It can also bend the other way, because in the hop study on this page the uninvolved knee did more work than the knees of uninjured athletes (Kotsifaki and colleagues, 2022). And a symmetrical hop distance can hide an unsymmetrical knee, which is why strength is measured separately rather than inferred from a hop. Treat a single percentage as one piece of information rather than a verdict, and ask which test it came from.
Can I go back to sport at 6 months after ACL surgery?
Some people do, and the research says the risk is higher the earlier it happens. In a study of 106 people who played pivoting sports, the rate of injuring the knee again fell by about half for each month the return was delayed, up to 9 months after surgery, with no further drop after that (Grindem and colleagues, 2016). Returning to that level of sport at all carried a reinjury rate over four times higher than staying below it in the same study. OrthoInfo describes most people being allowed back to full sport within 6 to 12 months, depending on their progress, strength and movement, and the van Melick guideline advises that rehab carries on for 9 to 12 months. Nobody can tell you from the month alone, which is the reason the tests exist, and the decision belongs to your surgeon and physio with you.
Do I need a knee brace when I go back to sport?
If your surgeon gave you a brace and told you to wear it, wear it, and nothing on this page is a reason to take it off. Where the evidence sits is this: a best-evidence synthesis of systematic reviews produced for the OPTIKNEE consensus found moderate certainty evidence that knee bracing after an ACL reconstruction provides no benefit for knee laxity or physical function, drawing on one systematic review of seven randomized trials, and it also found low certainty evidence that bracing has no effect on self-reported function or pain. Of the 22 reviews that overview included, none had looked at prevention of reinjury (Culvenor and colleagues, 2022). An earlier systematic review of 15 studies put it this way: the effectiveness of functional bracing after this operation remains unclear, some data suggest it may help knee movement mechanics and may offer the graft some protection without costing function or range, and limited evidence exists to support routine bracing as a way to lower the rate of reinjury (Lowe and colleagues, 2017). OrthoInfo, from the American Academy of Orthopaedic Surgeons, says a functional brace is not necessarily required when returning to sport after a successful ACL reconstruction, although some patients feel more secure wearing one. So a brace has not earned a place as routine kit on the evidence, and whether it lowers the risk of a second injury has barely been studied. If you want to wear one because it helps your confidence, say so to your surgeon and physio and let them answer it for your knee.
What happens if I fail return to sport testing?
You get a list, which is more useful than a date. A failed item tells your physio what to train, and most of the time it is thigh strength, landing control on one leg, or confidence, each of which responds to specific work over the following weeks or months. Nothing about failing means the operation went wrong. In the Grindem study, 38.2% of those who did not pass the criteria went on to injure the knee again, against 5.6% of those who did pass, although with these numbers that difference did not reach statistical significance (p=0.075), so the honest summary is that passing looks better rather than that it is proven protective. Ask for the retest date and what has to change before it.
References
- Briem K, Zebis MK, Haraldsson BÞ, Bencke J, Fernandes L. Rehabilitation guidelines after autograft anterior cruciate ligament reconstruction need more graft-specific exercise recommendations: A scoping review. Knee Surgery, Sports Traumatology, Arthroscopy. 2026;34(1):83-101. https://doi.org/10.1002/ksa.12666
- Kotsifaki R, Korakakis V, King E, et al. Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction. British Journal of Sports Medicine. 2023;57(9):500-514. https://doi.org/10.1136/bjsports-2022-106158
- van Melick N, van Cingel REH, Brooijmans F, et al. Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus. British Journal of Sports Medicine. 2016;50(24):1506-1515. https://doi.org/10.1136/bjsports-2015-095898
- Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. British Journal of Sports Medicine. 2016;50(13):804-808. https://doi.org/10.1136/bjsports-2016-096031
- Kotsifaki A, Whiteley R, Van Rossom S, et al. Single leg hop for distance symmetry masks lower limb biomechanics: time to discuss hop distance as decision criterion for return to sport after ACL reconstruction? British Journal of Sports Medicine. 2022;56(5):249-256. https://doi.org/10.1136/bjsports-2020-103677
- Kotsifaki A, Korakakis V, Graham-Smith P, Sideris V, Whiteley R. Vertical and Horizontal Hop Performance: Contributions of the Hip, Knee, and Ankle. Sports Health. 2021;13(2):128-135. https://doi.org/10.1177/1941738120976363
- Culvenor AG, Girdwood MA, Juhl CB, et al. Rehabilitation after anterior cruciate ligament and meniscal injuries: a best-evidence synthesis of systematic reviews for the OPTIKNEE consensus. British Journal of Sports Medicine. 2022;56(24):1445-1453. https://doi.org/10.1136/bjsports-2022-105495
- Lowe WR, Warth RJ, Davis EP, Bailey L. Functional Bracing After Anterior Cruciate Ligament Reconstruction: A Systematic Review. Journal of the American Academy of Orthopaedic Surgeons. 2017;25(3):239-249. https://doi.org/10.5435/JAAOS-D-15-00710
- Rambaud AJM, Ardern CL, Thoreux P, Regnaux JP, Edouard P. Criteria for return to running after anterior cruciate ligament reconstruction: a scoping review. British Journal of Sports Medicine. 2018;52(22):1437-1444. https://doi.org/10.1136/bjsports-2017-098602
- D'Ambrosi R, Helito CP, Della Villa F, et al. Practice patterns, controversies, and proposed management algorithm for cyclops syndrome after anterior cruciate ligament reconstruction: An international survey. Journal of ISAKOS. 2026;19:101165. https://doi.org/10.1016/j.jisako.2026.101165
- NHS. Recovering from ACL (anterior cruciate ligament) surgery. Page last reviewed 17 July 2025. https://www.nhs.uk/tests-and-treatments/acl-anterior-cruciate-ligament-surgery/recovering/
- American Academy of Orthopaedic Surgeons. ACL injury: does it require surgery? OrthoInfo. https://www.orthoinfo.org/en/treatment/acl-injury-does-it-require-surgery/
- NHS. Deep vein thrombosis (DVT). Page last reviewed 30 April 2026. https://www.nhs.uk/conditions/deep-vein-thrombosis-dvt/
- NHS. Compartment syndrome. Page last reviewed 4 September 2026. https://www.nhs.uk/conditions/compartment-syndrome/
- NHS. Pulmonary embolism. Page last reviewed 25 May 2023. https://www.nhs.uk/conditions/pulmonary-embolism/
- NHS. Sepsis. Page last reviewed 14 May 2026. https://www.nhs.uk/conditions/sepsis/
Written and checked by the PocketPhysio editorial team. Last updated 2026-10-24.
This page is general education, not a diagnosis or a personal treatment plan. See a physiotherapist or doctor for advice about your own situation.