Part of ACL reconstruction rehab
ACL return to running: what has to be true before your first run
Warning signs, and when to get help
What has to be true before your first run
Seven things, and one more that is not on any list at all. The seven come from the Aspetar guideline, which proposed them for a return to running at a volume and intensity that gives a cardiovascular training effect, and which physios check before a first run rather than after it: full straightening, bending at least 95% as far as the other knee, no more than a trace of swelling, thigh strength more than 80% of the other leg, more than 80% of the other leg on a countermovement jump measure, pain-free hopping on the spot on one leg, and pain-free jogging in water or on an anti-gravity treadmill before you run on land (Kotsifaki and colleagues, 2023).
That last one needs a pool or an anti-gravity treadmill, and many clinics have neither. It stays in the list because the guideline put it there, and because it shows how gradually impact is meant to arrive. Where the equipment is not there, the practical answer is that your physio builds toward running another way, with low impact work and hopping on land, rather than counting the item as met and moving on. No pool does not mean you are stuck. It means the item is not one you can tick off at home, and whether impact has been built up gradually enough is a judgement for the person who can watch you hop.
How that list was made changes how you should use it. The guideline group says it proposed these criteria despite an absence of research findings, so they are the agreement of experienced clinicians rather than tested thresholds. They are still the best described starting point anyone has published, and they are measured, not guessed. That is their real advantage over a date.
Swelling and thigh strength are the two items not to bend on. More than a trace of swelling means the joint is still reacting to what it has already been given. And a thigh still well below the other side is the deficit that research ties to injuring the knee again, although that research followed people going back to pivoting sport rather than people starting to run, so read it as a reason to take the strength item seriously rather than as evidence about a first run (Grindem and colleagues, 2016). Running on a knee with either of those is not a shortcut that costs nothing.
The thing that is not on any list is your surgeon's permission, and it outranks all seven. If a meniscus or cartilage repair was done in the same operation, impact often waits longer than the ACL itself would need, and how much longer is not something a page can tell you. In a systematic review of rehabilitation after meniscal repair done on its own, protocols varied widely and agreed on neither range of motion nor weight bearing (O'Donnell and colleagues, 2017), and a repair done alongside an ACL reconstruction was outside what that review could study. Cartilage repairs are usually held back further still, because the repaired surface takes load through every stride. Ask the team who did your operation when impact is allowed, and take their answer over the criteria above and over any date.
Where that work gets done is stage 3 and stage 4 of the ACL reconstruction rehab program, and the exercises that build each criterion are set out in ACL rehab exercises by phase.
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). That can put the hopping criterion later than the 12 week mark most protocols use for running, which is one more reason the date comes from your own team rather than from a list.
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 hopping criterion is the one people most often meet last, and pogo hops and the single leg hop and hold are where it is trained and tested.
When can you run after ACL surgery?
In most published programs, not before about 12 weeks. The figure is real and it is constantly misread. Where it came from matters more than the number.
A scoping review collected the criteria used for return to running after ACL reconstruction across 201 studies. It found 205 time-based criteria. The median was 12 weeks, the range ran 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). That makes 12 weeks the middle of a very wide spread of what teams decided to do, not a point at which anything is known to have healed.
The Aspetar guideline is blunt about the gap that leaves: it says there are no conclusive results on whether returning to running at or before 12 weeks is safe, and that the prospective studies which would show whether running at 12 weeks brings a new knee injury have not been done. Alongside that sits what we know about the graft itself. It goes in as a piece of tendon and is rebuilt over months into something more ligament like, and biopsy studies in people confirm the stages but do not agree on how long each takes (Claes and colleagues, 2011). Feeling strong is not the same as being healed, because the tissue doing the healing is not tissue you can feel.
On its own, the date tells you nothing. A date is not permission. The knee meeting the criteria, with your physio watching it happen and your surgeon's limits respected, is permission.
How the first runs are built
Small, flat, short and often paused. The shape most physios use is a walk-run: a few minutes of walking, then short bursts of easy running inside it, with the running time built up across sessions rather than within one.
As a rough guide from common practice, the first sessions are every other day rather than daily, on a flat and even surface, at a pace that lets you talk, with no hills, no turns at speed and nothing that asks the knee to change direction. Totals start at a handful of minutes of actual running. Your physio will adjust all of it to your knee, your graft and your sport, and they will often want to watch the first one.
Keep the strength work going rather than swapping it for running, because the strength is what earned you the run. And change one thing at a time: time on feet, or pace, or surface, never two together, so that when the knee complains you know what it was complaining about.
The return to running plan covers how a walk-run is built in more detail, and strength work for runners covers what to keep doing alongside it. The single leg heel raise, the supported single leg squat, the lateral step down with a band and the standing hamstring curl with a weight are the four that usually stay in the program through this stage.
What the knee tells you the next morning
The next morning is the judge, not how the run felt. Running is the first thing in this whole recovery that loads the knee quickly and repeatedly, and the response arrives hours later.
What is expected: a knee that feels worked, mild stiffness or an ache that settles, and a morning that looks like the one before. What is not: a knee that is clearly more swollen, a knee that is sorer than it was, or pain that built with every minute while you ran.
If the next morning is worse, drop back to the last session the knee tolerated and build from there, rather than stopping entirely or pushing on. Knee pain after running covers the common patterns, and a swollen knee covers what the swelling itself means.
Some things are not a dosing problem at all, and they belong to the warning signs at the foot of this page. A knee that gives way, pops or shifts and then swells within a few hours needs your surgical team the same day. A knee that locks needs the same. A first run is where both of those tend to appear.
Does the graft change when you can run?
It can change how long it takes you to meet the criteria, which is a different claim from changing the criteria themselves.
The clearest comparison we could find looked at thigh strength, not at running itself. In a retrospective study of 73 patients after anatomic ACL reconstruction at one center, the group with a quadriceps tendon graft had a lower quadriceps index at 5 to 8 months than the patellar tendon and hamstring graft groups, and fewer of them met that clinic's 80% thigh strength mark for return to running at that stage, 26% against 60% for patellar tendon grafts. Only 52 of those patients were measured again at 9 to 15 months, and by then the difference between the grafts was no longer statistically significant, which the authors framed as a result limited by the numbers they had: their own conclusion was that the quadriceps tendon group still showed clinically meaningful thigh asymmetry at both time points (Hughes and colleagues, 2019). One center, looking back at its own records, is not strong evidence, so the fair reading is that grafts can differ in how fast the thigh recovers, not that one graft runs sooner than another.
Pain at the front of the knee is more common after a patellar tendon graft (OrthoInfo), and that is the kind of pain the Aspetar guideline advises adjusting the load for rather than running through. After a hamstring graft, loaded hamstring work is held back early and the evidence on exactly when to start it is unclear (Högberg and colleagues, 2026), which matters because the hamstrings are working hard in a stride. What each graft takes and what settles is covered in hamstring compared with patellar tendon graft.
Why your physio tests instead of counting the weeks
Because the things that predict trouble are measurable, and the week number is not one of them.
The pattern that shows up in the research is about strength and timing, not dates. 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 to sport was delayed, up to 9 months, and people whose thigh strength was closer to the other leg had fewer reinjuries (Grindem and colleagues, 2016). The van Melick guideline recommends a battery of strength, hop, movement quality and psychological tests to decide when somebody progresses, and advises that rehab carries on for 9 to 12 months after surgery (van Melick and colleagues, 2016).
Running is a step inside that, not the end of it. Getting back to sport has its own, longer set of tests, and they are covered in ACL return to sport testing. Why that gap matters for the rest of your life with this knee is in preventing a second ACL injury, and the dates everything sits inside are on the ACL surgery recovery timeline.
Take one question to your next appointment, in these words: which of the running criteria have I not met yet. That answer tells you what to train. A month cannot.
This page is general education and not advice about your own knee, and it does not stand in for the post-operative review your surgeon and physio do before you run. Where their instructions differ from anything here, theirs come first. The decision to let you run belongs to the people who can examine the knee.
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
When can I start running after ACL surgery?
When your physio has tested the knee and says the criteria are met, and not before about 12 weeks in most programs. The Aspetar guideline suggests checking full knee straightening, bending at least 95% as far as the other knee, no more than a trace of swelling, thigh strength and a jump measure each more than 80% of the other leg, pain-free hopping on the spot on one leg, and pain-free jogging in water or on an anti-gravity treadmill first. Those criteria came from expert agreement rather than from research findings. The 12 weeks comes from a scoping review of 201 studies, where it was the median of the time-based criteria used, with a range from 5 to 39 weeks (Rambaud and colleagues, 2018), so read it as the middle of a spread of protocols. Ask your physio for a running assessment rather than asking whether the date has arrived.
Is 3 months too early to run after ACL surgery?
For some knees yes, and nobody can tell from the week number alone. About 12 weeks is where most of the protocols in the research sit, and the Aspetar guideline says there are no conclusive results on whether running at or before 12 weeks is safe. What decides it for you is the list of criteria, not the month: a knee with more than a trace of swelling, or a thigh still well below the other side, is not ready at 12 weeks or at 16. A meniscus or cartilage repair done in the same operation often pushes impact later again, and that limit belongs to your surgeon. If you had one, ask them before you run rather than assuming the ACL timeline covers it.
Why does my knee swell after running?
Swelling the next day is the most useful signal you get, and it usually means the run asked for more than the knee could take. The practical response is to go back to the last session the knee tolerated, repeat it until the next morning is clean, and build again from there. Tell your physio either way, because they may want to see the knee and check whether the criteria you passed still hold. Swelling that comes up within a few hours after the knee gave way, popped or shifted is a different matter entirely, and the warning signs on this page give that one a same day route. A knee that is hot, or swollen alongside a temperature, is not an overdone run either.
Does graft type change when I can run?
It can change how quickly you meet the criteria, which is not quite the same thing. In a retrospective study of 73 patients, the group with a quadriceps tendon graft had lower thigh strength at 5 to 8 months than those with a patellar tendon or hamstring graft, and fewer of them met the 80% thigh strength mark used for return to running at that point, 26% against 60% for patellar tendon grafts. By 9 to 15 months the difference was no longer statistically significant, although only 52 patients were measured that far out and the authors still concluded that the quadriceps tendon group had clinically meaningful thigh asymmetry at both time points (Hughes and colleagues, 2019). It was one center, looking back at records, so treat it as a reason to expect differences, not a schedule. The published running criteria themselves are the same whatever graft you had.
Should my first run be on a treadmill or outside?
Either can work, and the things that matter more are the surface, the distance and what you do the day after. Most physios start people on a flat, even surface with no camber, no hills and no turns at speed, which rules out trails and a cambered road edge early on. A treadmill makes the pace steady and the surface predictable, which some people find easier to hold back on, while others find the belt encourages a longer stride than they would choose. Pain-free jogging in water or on an anti-gravity treadmill is one of the criteria the Aspetar guideline proposes before a first run on land at all, which tells you how cautiously these first sessions are usually built. Ask your physio which they would rather you used, and take the answer with their walk-run plan.
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
- 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
- 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
- Hughes JD, Burnham JM, Hirsh A, Musahl V, Fu FH, Irrgang JJ, Lynch AD. Comparison of Short-term Biodex Results After Anatomic Anterior Cruciate Ligament Reconstruction Among 3 Autografts. Orthopaedic Journal of Sports Medicine. 2019;7(5):2325967119847630. https://doi.org/10.1177/2325967119847630
- Högberg J, Wernbom M, Hamrin Senorski E. Can we rebuild what has been taken? A narrative review of biological and functional consequences of hamstring tendon harvest in ACL surgery. Science Progress. 2026;109(3):00368504261461371. https://doi.org/10.1177/00368504261461371
- O'Donnell K, Freedman KB, Tjoumakaris FP. Rehabilitation Protocols After Isolated Meniscal Repair: A Systematic Review. American Journal of Sports Medicine. 2017;45(7):1687-1697. https://doi.org/10.1177/0363546516667578
- Claes S, Verdonk P, Forsyth R, Bellemans J. The "ligamentization" process in anterior cruciate ligament reconstruction: what happens to the human graft? A systematic review of the literature. American Journal of Sports Medicine. 2011;39(11):2476-2483. https://doi.org/10.1177/0363546511402662
- 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.