Training guide
Knee mobility means bending the knee and getting it fully straight. Stairs and chairs need about 90 to 120 degrees of bend, and a knee that won't straighten changes how you walk. Moving a stiff knee little and often, stretching the front and back of the thigh and using the range on chairs and steps all help, and a big loss of movement isn't just age.
This guide covers how far a knee should bend and straighten, a simple check, what the evidence shows for healthy knees, arthritis and after surgery, the moves with doses, a step-by-step session and our new 12-minute knee mobility routine, and when a knee that locks, won't straighten or stays stiff after an operation needs its team or our knee pain guides.
Walking and slopes use under 90 degrees of knee bend, stairs and chairs 90 to 120, getting out of a bath about 135 and a heels-up deep squat about 157. Losing the last few degrees of straightening went with worse pain and function in knee arthritis, and with worse long-term results after ACL (anterior cruciate ligament) surgery.
In a US national survey, knee and hip range was only 3 to 5 degrees smaller at 65 to 74 than in younger adults, and the authors call any substantial loss abnormal. A knee that has lost a lot of movement is worth getting checked.
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In healthy young adults, hamstring stretching added about 8 to 12 degrees across 19 trials, one 30-second hold a day was enough, and strength training through a full range matched stretching. Range slips back within weeks if you stop.
Heel slides, quad sets with the heel on a rolled towel, and gentle stretches for the front and back of the thigh, a few at a time, 2 or 3 times a day, as NHS inform's knee exercises suggest; then use the range on chairs and steps. Our knee mobility routine puts it together.
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With knee arthritis, exercise is a core treatment for pain and function, though few trials measured range. After a knee replacement, a knee that stalls in the first weeks doesn't reliably free up on its own, so tell your team early. After ACL surgery, getting the knee fully straight comes first.
Knees that bend back past straight need strength and control, not stretch. A knee that locks, won't straighten after a twist, gives way or swells needs checking first: see the warning signs.
The knee is a hinge between the thigh bone and the shin bone, with the kneecap gliding in a groove at the front, as our knee joint page explains. Knee mobility means two things: bending (flexion) and straightening fully (extension), with a little turning of the shin when the knee is bent.
Healthy knees straighten fully and bend until the thigh meets the calf. In 674 healthy people, women had a little more range than men and range fell with age, but in a US national survey knee range was only about 3 to 5 degrees smaller at 65 to 74 than in younger adults. Compare your two knees, and yourself over time, rather than a chart.
In 20 adults averaging 67, walking and slopes used under 90 degrees of bend, stairs and chairs 90 to 120, and getting out of a bath about 135. Crouching with a twist used about 149 degrees, and a heels-up deep squat about 157. Kneeling and sitting back on your heels need close to full bend. Straightening fully matters for walking: a knee that stays bent makes the thigh work harder, which is why our ACL and knee replacement guides put it first (our reading).
Swelling in the joint, the commonest reason a sore knee won't bend; the quadriceps at the front for bending, and the hamstrings and calf at the back for straightening; the joint capsule and scar tissue after surgery; arthritis changes; a torn meniscus that blocks straightening; and soft tissue, since at deep bends the thigh meets the calf, from about 121 degrees in men. Bigger thighs and calves meet sooner, and that's normal.
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Some knees bend back past straight (a few degrees is common, and more counts towards the Beighton score for hypermobility); very flexible knees need control, not stretch. Range is a little smaller with age, but a big loss isn't normal.
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Our suggestion, from the studies' methods. These guide your practice; they don't diagnose anything.
Lying on your back, slide one heel towards your bottom as far as is comfortable and note how close it gets, then compare sides. A phone app measured knee bend reliably to about 6 degrees in people with arthritis or a new knee.
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Sit with your legs out straight and see whether the back of each knee rests on the floor. Or lie face down with your knees just off the end of the bed and compare the heights of your heels: a heel that sits higher shows a knee that isn't straightening, a test that picked up losses under 10 degrees after ACL surgery.
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Retest every 2 to 4 weeks at the same time of day. By eye, only differences of about 14 degrees were clearly real in one study, so small changes may be measuring error.
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Healthy-knee trials are in young adults; the surgery evidence is mostly cohorts and guidelines.
In a US national sample of 1,683 adults aged 25 to 74, hip and knee range was only 3 to 5 degrees smaller in the oldest group, textbook norms differed from measured ones by up to 18 degrees, and the authors call any substantial loss of joint movement up to age 74 abnormal. In 674 healthy people, women had more range and range fell with age.
A phone app read knee bend reliably in 60 people with arthritis or a knee replacement, with a change of about 6 degrees of bend and 3 of straightening needed to be sure it was real. By eye or with a short goniometer, only differences of about 14 degrees were clearly real (6 knees, 3 raters). Comparing heel heights lying face down picked up a loss of straightening under 10 degrees in 50 people after ACL surgery.
In 20 adults averaging 67, walking and slopes used under 90 degrees of bend, stairs and chairs 90 to 120 and a bath about 135, and the authors suggest 110 as a rehabilitation goal. A heels-up deep squat needed about 157 degrees in 30 adults and crouching with a twist about 149 in 26; the thigh met the calf from about 121 degrees in 58 men.
In 8,667 knees of people with knee arthritis, a knee that wouldn't go fully straight went with worse pain, stiffness and function, more so the bigger the loss. It's a snapshot, so it can't show which came first.
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Exercise improves knee arthritis pain and function across 139 trials of 12,468 people (low to moderate certainty), and NICE recommends it for everyone with osteoarthritis. Range wasn't one of the outcomes.
Whether exercise improves knee range in arthritis is barely tested: across 33 trials, range was measured in 1. Across 72 trials, the smallest change in knee bend that people with arthritis notice was about 4 to 6 degrees.
Stretching eased knee arthritis pain across 19 trials. In one small trial of 60 people over 45, adding therapist-applied stretching of the front of the thigh to a 4-week programme raised knee bend from about 97 to 124 degrees, against 95 to 103 with the programme alone, an unusually large gain from a single study. PNF (contract-relax) stretching added about 10 degrees in 2 small trials (very low certainty), and in 44 people with kneecap pain, static and moving quad stretches did equally well over 6 months, with no untreated group.
Across 19 trials in healthy young adults, static hamstring stretching added about 8.6 degrees of knee straightening on one test, 8.4 on another and 12 on the straight-leg raise. In 93 adults, one 30-second hold a day worked as well as 60-second holds or 3 a day, and strength training through a full range matched stretching across 11 trials. We found no trial of quad stretching that measured knee bend in healthy adults.
In 18 students, a 9-degree gain was back to where it started 4 weeks after stopping. Across 13 studies, range stayed above baseline after 2 to 6 weeks off but slipped from its peak, and only in inactive people.
Across 49 studies of 2,135 people with joint contractures (joints stiffened in one position), stretching for less than 7 months had no clinically important effect on range. A knee that has been stuck for months needs a GP or physiotherapist, not a home stretch alone.
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An international consensus grades stiffness by bend (mild at 90 to 100 degrees, severe under 70) and by how far short of straight (mild at 5 to 10 degrees, severe over 20). Bend under 90 degrees beyond 12 weeks affected about 4% across 35 studies of 48,873 knees. In 137 people, bend went from a median of 80 degrees in week 1 to 110 at 8 weeks, and knees under 90 at 8 weeks had barely improved since week 4. In 559 people, most change came in the first 12 weeks, from about 100 degrees at 2 weeks to 117 at a year, and range reached a plateau by 12 months in 145 knees.
Physiotherapy exercise added about 4 degrees of bend at 6 months and 2 at 12 months against minimal physiotherapy across 18 trials. A bending machine (CPM, continuous passive motion) added about 2 degrees with no effect on function across 24 trials, and a 2026 US guideline strongly recommends against it while recommending range exercises; active heel slides matched CPM for range in a trial. NICE asks for rehabilitation to start on the day of surgery if possible, with a home exercise programme.
Moving a stiff new knee under anaesthetic took most past 90 degrees, best within 12 weeks, across 22 studies of 1,488 people. Early manipulation gained 32 degrees against 19 for later, with similar final bend, across 14 studies of 13,445 knees, and a consensus recommends it between 6 weeks and 3 months. These are observational studies.
Across 36 studies, 36.8% of people could kneel at 1 year and 47.6% after 3 years. Squatting with high-flexion implants went with how far the knee bent before surgery (300 knees), and high-flexion implants added bend but not function across 22 trials.
Losing 3 to 5 degrees of straightening, counting any natural hyperextension, went with worse results 10 years or more later in 502 people, and abnormal movement with twice the odds of arthritis on X-ray in 539. In 3,633 people, a loss of straightening at 6 weeks went with about 8 times the odds of a cyclops lesion, a nodule of scar tissue that blocks straightening, and across 12 studies a loss of straightening went with pain at the front of the knee.
Guidelines start movement early, and one uses full straightening and about 95% of knee bend among its checks before running (expert opinion). Another says CPM didn't improve final movement, and a third uses phases based on goals met over 9 to 12 months. Our ACL surgery guide has the plan.
Very flexible joints went with more knee injuries in contact sport across 18 studies. In female footballers after ACL surgery, a knee bending back more than 5 degrees went with a second ACL injury but not a first.
Blocking the knees from passing the toes cut knee load from 150 to 117 newton metres but raised hip load from 28 to 303 in 7 men, restricted squats changed trunk movement in 30 people, and restricting knee travel gave no benefit over 6 weeks of training in 57 adults. Deep squats haven't been shown to harm healthy knees, though an older review prefers parallel squats for athletes. Stress behind the kneecap is lowest from 45 degrees of bend to straight, and a review of squats and kneecap pain points to 60 to 90 degrees under load as the most provocative range.
Working in a squat or kneeling for more than 30 minutes a day went with knee arthritis across 80 studies, and the odds rose about 1.26 times for every 5,000 hours of kneeling. These are observational studies of years of work. Our reading is that they don't tell you about squats as exercise, which haven't been shown to harm healthy knees.
NHS inform's knee exercises hold the lying knee bend for 2 seconds and static quads for 10, 2 to 3 repetitions at a time through the day, building to sets of 8 and at most 2 sets of 15, with stretches held 20 to 30 seconds, 2 to 3 sets, 2 to 3 times a day. This is guideline advice; no trial has compared doses.
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Two or three times a day: heel slides, 10 slow each side with a 2-second pause at the end; quad sets with the heel on a rolled towel, 10 holds of 5 seconds (our yoga after a knee replacement session; NHS inform holds them for 10); and gentle stretches for the front and back of the thigh, held 20 to 30 seconds, as NHS inform suggests. Keep to the knee pain rule in the warning signs.
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Hold stretches 30 to 60 seconds on most days, and strengthen through a full range with a load at least twice a week, as our flexibility guide sets out: deeper squats, split squats and step-downs to the depth you control, stopping 2 or 3 reps short of failure, as our plans advise.
Rest your heel on a rolled towel with nothing under the knee and let the leg relax straight, 1 to 2 minutes at first and building towards 5 to 10, as our ACL surgery guide's heel prop does; then tighten your thigh to press the back of the knee down. Don't rest with a pillow under the knee, which can stop it getting fully straight, as our knee replacement guide says.
Sit-to-stands from a chair, step-ups and squats to the depth you control, 2 or 3 times a week (our knee strengthening workout and squat technique workout). Range you use in daily life is the range that lasts.
Stretching trials gained range over a few weeks. After a knee replacement, most bend returns in the first 12 weeks and keeps improving to about a year. Gains fade within weeks of stopping, so keep going 2 or 3 days a week once you're happy.
Measure every 2 to 4 weeks with a phone app or the heel-to-bottom distance, at the same time of day (our suggestion). Small changes may be measuring error.
Resting with a pillow under the knee; forcing a bend through sharp pain or swelling; bouncing in stretches; working only on the bend and forgetting the last few degrees of straightening; kneeling or deep bends before your team clears them after surgery (our editorial list). Each move's page teaches its technique.
Our editorial session, from NHS inform's knee exercises (the lying knee bend held 2 seconds, static quads, stretches held 20 to 30 seconds, 2 to 3 times a day), our ACL surgery guide's written steps and our knee strengthening workout. After surgery, your team's plan and limits come first.
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The movement on the figure: Supine heel slide
Slow and to a comfortable stretch, little and often while the knee is stiff. For heel slides, the move page's dose is "10 slow repetitions each side, once or twice a day. An editorial starting point: there are no trials of this movement on its own." NHS inform holds the same move for 2 seconds at the end. Quad stretches on your side, standing or face down: hold 20 to 30 seconds, 2 to 4 times each side (our editorial starting point); the side-lying versions suit a stiff knee, as the standing stretch's page says. Easy cycling for 5 minutes with the saddle high enough that your knee stays slightly bent at the bottom (our cardio machines for beginners session); rocking the pedals back and forth before full turns suits a knee that can't yet bend far enough (our suggestion). Knee to chest takes the knee into a gentle full bend: hold 20 to 30 seconds, 2 to 4 times each side (our editorial starting point), and avoid deep or repeated rounding with osteoporosis.
3D demoSupine heel slideBeginner · No equipment
3D demoSide-lying quad stretchBeginner · No equipment
3D demoStanding quad stretchBeginner · A wall
3D demoFace-down quad and hip flexor stretch with a strapIntermediate · Other / check instructions
3D demoStationary cyclingBeginner · Cardio machine
3D demoSingle knee-to-chest stretchBeginner · No equipmentGetting fully straight matters as much as bending. Quad sets at 10 holds of 5 seconds, heel on a rolled towel, nothing under the knee (our yoga after a knee replacement session), which is also the heel prop position. Seated knee extensions, 10 each leg with no weight, straightening fully and pausing (our knee mobility routine). The hamstring stretch with a strap at 2 holds of 30 seconds each leg, letting the knee straighten as far as is comfortable (our yoga after a knee replacement session); for the standing or sitting hamstring stretch, the move page's dose is "Hold 30 seconds, 1 to 3 times each leg, at least 5 days a week. In a trial, one 30-second hold a day gained as much hamstring range over 6 weeks as 60-second holds or three holds a day." Straight-leg raises at 10 each side, the other knee bent (our low-impact leg workout), only once the knee straightens fully as you tighten the thigh. The face-down quad stretch's demo shows the position for our ACL surgery guide's prone hang.
3D demoQuad set (static quads)Beginner · No equipment
3D demoSeated knee extension (chair)Beginner · A bench or box + Something with weight
3D demoSupine hamstring stretch with a strapBeginner · No equipment
3D demoLying hamstring and calf stretch with a strapBeginner · Other / check instructions
3D demoStraight-leg raiseBeginner · No equipmentRange you can use, 2 or 3 times a week: sit-to-stands at 2 sets of 8, touching the seat without dropping into it, then a lower seat (our squat technique workout); step-ups at 8 each side on a stable step with a hand on a rail (our knee strengthening workout); backward walking at 5 to 10 minutes, most days (the move page's dose); knee circles at 5 slow circles each way (our knee strengthening workout); and goblet squats at 3 sets of 5, 3 seconds down and a 1-second pause, to the depth you control (our squat technique workout).
Stairs and chairs need about 90 to 120 degrees of bend, and kneeling or sitting back on your heels much more, until the thigh meets the calf. Practise the movement itself: sit-to-stands to a lower seat and step-ups to a higher step, a little further each week.
A heels-up deep squat needed about 157 degrees of knee bend. Let your knees travel forward as far as your ankles allow, as our squat guide says: holding them back moved the load to the hips and back in a lab study and gave no benefit in a 6-week trial. Our squat depth guide covers the rest.
Exercise is a core treatment for knee arthritis pain and function. Work on getting fully straight as well as bending, since a knee that won't straighten went with worse symptoms; about 4 to 6 degrees more bend is a change people notice. Our knee arthritis guide has the plan.
Bend usually reaches about 110 degrees by 8 weeks and keeps improving to about a year, but a knee that stalls early tends to stay behind, and manipulation gained more when done early. Active exercises do the work; a bending machine adds little. Follow your team's plan, and tell them early if the knee isn't bending or straightening: our knee replacement guide has the stages and its threshold.
Getting fully straight comes first, then the bend, at your team's pace: a loss of straightening still there at 6 weeks went with scar nodules that block it, and small losses with worse results years later. Our ACL surgery guide has the heel prop, the prone hang and the checks before running.
Knee range changes little with age, so a stiff knee is worth working on rather than accepting. The NHS asks adults over 65 for activities that improve strength, balance and flexibility on at least 2 days a week, and sit-to-stands and step-ups count towards it.
Our knee mobility routine bends and straightens the knee, then uses the range in chairs and steps, in about 12 minutes. While a knee is stiff, do the bending and straightening part 2 or 3 times a day; the knee strengthening workout builds the muscles that move it.
A 12-minute routine for a stiff knee: warm it up, bend it, get it fully straight, stretch the front and back of the thigh, then use the range in chairs and steps.
12 minBeginner9 movesA bench or box, Something with weightA 25-minute session for knees that don't currently hurt: thigh and hamstring strength, single-leg control, then an optional full-range block with knees over toes.
25 minBeginner14 movesA bench or box, A wallRoll the thighs and calves, stretch the front of the thigh, then the hip and knee strength work that helps knee pain. About 15 minutes.
15 minBeginner10 movesA foam roller, A bench or boxA gentle leg strength routine with no jumping: sit-to-stands, step-ups, wall sits, bridges and calf raises.
20 minBeginner7 movesA bench or box, A stepA 30-minute joint-friendly circuit built like the GLA:D and ESCAPE-pain programmes: a gentle warm-up, chair, step and band strength moves, balance, then stretches.
30 minBeginner14 movesA bench or box, A stepA 25-minute knee-friendly yoga practice with no kneeling and no deep bends: shallow standing poses, hip and thigh strength on the floor, and supported stretches.
25 minBeginner15 movesFirm cushionA 25-minute Pilates class for sore knees and knee arthritis: lying and side-lying leg work, shallow squats and balance, with no kneeling at all.
25 minBeginner15 movesA bench or box, Something with weightA 25-minute kneel-free yoga class for after a knee replacement: seated breathing, standing poses at a chair, gentle bends lying down and a heel-supported rest.
25 minBeginner18 movesA bench or box, Something with weightA 25-minute practice session for the squat: find your depth on a chair, groove the bodyweight squat with pauses, then load it with a slow goblet squat.
25 minBeginner8 movesA wall, A bench or boxThe plan for seniors builds strength and balance around the knee, the 30-day squat challenge has a chair track, and the runners' strength plan loads the knee through its range.
A 12-week exercise plan for over-65s: strength and balance three times a week, short balance sessions and daily walks, based on falls-prevention trials.
3 training days40 minBeginner3 days a weekA free 30-day squat challenge with a chair track and a single-leg track: 3 short sessions a week, optional practice days and a before-and-after test.
3 training days15 minBeginner2 days a weekA 12-week strength plan for runners: two sessions a week of heavy lifts, single-leg work, calf raises and hops, fitted around your runs.
2 training days45 minBeginnerWith a swollen knee, bending is usually limited by the swelling itself: settle the swelling and see our swollen knee guide rather than forcing the bend. Never force a knee that locks, gives way or is blocked from straightening; it needs checking first, as the warning signs say (our suggestion, following our knee pain hub).
The knee is not bending to about 90°, or not getting straight, by around 6 weeks, or it was moving well and is getting stiffer: tell your physiotherapist or surgical team now rather than waiting for a routine appointment. Stiffness is easier to treat early. (The 6-week check is our threshold, built from NHS trust leaflets.)
Don't rest or sleep with a pillow under the knee: it can stop the knee getting fully straight. Support the calf and heel instead (our suggestion, following our knee replacement guide).
The knee isn't getting fully straight in the first weeks, or the bend isn't coming back as expected: tell your physiotherapist or surgical team promptly. One NHS protocol advises acting promptly on pain, inflammation or limited movement that persists, because the knee can stiffen with scar tissue.
Follow your surgical team's limits. Our knee replacement, hip replacement and ACL (anterior cruciate ligament) injury guides cover the stages.
Squats are usually part of the answer. Avoid deep loaded squats at first, then build depth as your knee allows, as our knee arthritis guide explains.
Start with squats to about 45 degrees of knee bend, where the stress behind the kneecap was lowest, and deepen them as the pain allows. A little more forward lean and a wider stance shift work to the hips early on. Our runner's knee guide has the plan.
Knees that bend back, with joint pain, repeated sprains, joints that slip out, tiredness or poor balance: see a GP about joint hypermobility syndrome.
If you're already very flexible, put your time into strength and control through the range you have. Stretch only areas that feel genuinely tight, and only to a mild pull, and avoid hanging at the end of your range or pushing joints back past straight. The strength and control moves below are a place to start, and our hypermobility guide has a full routine, the evidence and the warning signs. If you do Pilates, our Pilates for hypermobility guide covers which moves to adapt.
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With osteoporosis or a past spinal fracture, avoid repeated or loaded deep rounding of the back, and bend from the hips. The osteoporosis guide covers impact and lifting.
In later pregnancy, do the floor moves on your side or sitting rather than lying flat on your back for long, and follow our pregnancy guide (our suggestion, following its advice to keep time flat on your back short after the first trimester).
If you get chest pain or pressure, feel faint or dizzy, are unusually breathless, or your heart races or beats irregularly during exercise, as our plans advise.
For chest pain that comes on suddenly and doesn't go away, feels tight or like squeezing, spreads to your arms, neck, jaw, stomach or back, or comes with sweating, feeling sick, light-headedness or breathlessness; severe difficulty breathing; someone who faints while exercising; palpitations that don't go away, or come with chest pain, shortness of breath or feeling faint; or a headache that starts suddenly and is extremely painful, especially while lifting or straining, or comes with numbness or weakness, difficulty speaking or loss of vision. The NHS says a bleed on the brain may be more likely when lifting something heavy. Don't drive yourself to A&E.
Go to A&E (accident and emergency) if you've injured your knee and it has changed shape, it becomes very swollen very quickly, you felt a pop or snap, you can see bone sticking out, or it's bleeding heavily. Don't drive yourself: ask someone to take you, or call 999 if the pain means you can't move your leg to get there.
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Get advice from NHS 111 now: you cannot move the knee or put any weight on it, or it is very painful, badly swollen or has changed shape.
Get advice from NHS 111 now: the knee locks, gives way or clicks painfully. Painless clicking is normal.
Get advice from NHS 111 now: after a twist, your knee won't go fully straight, or something blocks the last part of straightening, even if you can still walk on it. A torn piece of meniscus caught in the joint can do this, and it needs checking promptly.
Get advice from NHS 111 now: a hot, red or swollen knee with sudden severe pain, a very high temperature, or feeling hot, cold or shivery. This can be a joint infection.
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You hurt your knee and cannot take 4 steps, or you are 55 or over and have injured it: get it checked the same day for a broken bone.
A pop or tearing feeling at the front of the knee after a fall, a jump, a landing or a heavy squat, then you can't straighten the knee or lift the straight leg, there's a dent above or below the kneecap, or the kneecap sits higher or lower than on the other side. Go to A&E or an urgent treatment centre, or get help from NHS 111, as our knee pain when squatting guide explains. In the US, go to urgent care or the emergency department.
Same day (urgent GP appointment or NHS 111): throbbing pain in one leg (rarely both), usually the calf or thigh; swelling in one leg (rarely both); red, blue or darkened skin; or swollen veins; or sudden worse pain and swelling around a lump at the back of the knee (a possible clot or a burst Baker's cyst).
Call 999 or go to A&E if breathing suddenly becomes difficult, if pain in your chest or upper back comes on suddenly with breathlessness or a very fast heartbeat, or if someone passes out. Do not drive yourself. It can be a blood clot that has reached the lungs.
After an injury, if you heard a crack, the limb has changed shape or is pointing at an odd angle, it is numb, tingling or has pins and needles, or the skin has turned blue or grey or feels cold.
If a stretch brings on a sudden sharp pain, a snap or a pop, and it's very painful or getting worse, there's a lot of swelling or bruising, or it hurts to walk or stand on the leg. In the US, contact your doctor or urgent care.
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The knee is not bending to about 90°, or not getting straight, by around 6 weeks, or it was moving well and is getting stiffer: tell your physiotherapist or surgical team now rather than waiting for a routine appointment. Stiffness is easier to treat early. (The 6-week check is our threshold, built from NHS trust leaflets.)
New or worsening pain, a limp or loss of function months or years after the operation: see your GP, who should refer you back to the orthopaedic team.
Tell your team early, and keep up the bending and straightening exercises. If the knee stays stiff, you may be offered a manipulation under anaesthetic. In observational studies it gained more movement when it was done within about 3 months of surgery.
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The knee isn't getting fully straight in the first weeks, or the bend isn't coming back as expected: tell your physiotherapist or surgical team promptly. One NHS protocol advises acting promptly on pain, inflammation or limited movement that persists, because the knee can stiffen with scar tissue.
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Knee pain that has not improved within a few weeks of looking after it at home. Many areas offer NHS physiotherapy without a GP referral.
Numbness, tingling or weakness that travels down the leg from the back. That points to a nerve (sciatica) rather than the knee.
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Knees that bend back, with joint pain, repeated sprains, joints that slip out, tiredness or poor balance: see a GP about joint hypermobility syndrome.
See a GP if you think you or your child have joint hypermobility syndrome, for example joints that keep dislocating, ongoing joint or muscle pain and stiffness, frequent sprains, tiredness even after rest, poor balance or thin, stretchy skin. A GP may check your Beighton score, arrange tests to rule out other conditions and refer you to a physiotherapist.
Slowly and with control, in the middle of your range, stopping short of locking your knees or elbows or hanging at the end of a joint's range. If a joint feels about to slip, stop or make the movement smaller (our editorial rule, the same as in our shoulder dislocation guide).
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Burning, tingling, numbness or pins and needles down an arm or leg while stretching usually means a nerve is under tension, so ease off to a position without it. A pinch at the front of the hip or ankle at the end of a stretch is the joint, so work below it. See a GP or physiotherapist if either keeps happening (our suggestion).
Stop straight away if you feel any pain or become unwell, the NHS says, and contact 111 if your symptoms worry you or don't go away.
Pain from 0 to 2 out of 10 is fine, and up to 5 is acceptable if your knee is back to its usual level by the next morning; for tendon pain just below or above the kneecap, keep it to 3 or less. Sharp, catching or giving-way pain, or new swelling, means stop. That's our knee guides' rule.
A dull ache in your muscles for a day or two after something new is normal. Joint pain that's sharp, gets worse during a set or lingers into the next day means switching to the easier option, and seeing a GP or physiotherapist if it carries on (our plans' rule). Our muscle soreness guide has more.
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Ask for an urgent GP appointment or get help from NHS 111 for a headache that's triggered or made worse by coughing, sneezing, bending down or exercising. In the US, contact your doctor or urgent care.
Speak to your GP first if you haven't exercised for some time or have medical conditions or concerns, as the NHS advises. Get advice before heavy lifting or hard straining work if your blood pressure is uncontrolled, or you have heart disease or chest pain when you're active, a pacemaker or defibrillator, diabetic eye disease, glaucoma, a hernia, recent eye or tummy surgery, or you're pregnant, as our breathing guide lists. After a recent shoulder dislocation or shoulder surgery, follow our shoulder dislocation guide or your surgical team first.
Speak to a GP first if you haven't exercised for some time, or if you have a medical condition or concerns. Get advice first, too, if you have a health problem, an injury or symptoms, have recently had a heart attack or an operation, or are pregnant or have recently given birth.
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If you have a heart condition, follow your cardiac team's advice on how hard to work, and stop for the warning signs above. People with long-term conditions may wish to ask their specialist before starting. With uncontrolled high blood pressure, avoid straining against a held breath; the high blood pressure guide has more.
Knees under 90 degrees at 8 weeks after a replacement had barely improved since week 4 in one study, and manipulation gained more when done within about 3 months. Our knee replacement guide asks you to tell your team if the knee isn't bending to about 90 degrees by around 6 weeks.
It added about 2 degrees across 24 trials, with no effect on function, and a 2026 US guideline recommends against it. Active heel slides did as well in a trial.
Range was only 3 to 5 degrees smaller at 65 to 74 than in younger adults, and the authors call a substantial loss abnormal.
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Stretching alone for under 7 months had no clinically important effect on joint contractures across 49 studies. See a GP or physiotherapist.
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Blocking them moved the load to the hips and back, and restricting them gave no benefit in a 6-week training trial. Let them travel as far as your ankles allow.
We found no evidence of it: stretching added range in healthy adults and eased pain in knee arthritis. Don't force a stretch through sharp pain or into a swollen knee.
Very flexible athletes had more knee injuries in contact sport, and knees that bend back a long way need control rather than more range.
Squatting or kneeling at work for hours a day over years went with knee arthritis in observational studies. Our reading is that this doesn't apply to squats as exercise, which haven't been shown to harm healthy knees.
Bend and straighten the knee little and often with heel slides and quad sets, stretch the front and back of the thigh, and use the range on chairs and steps. Stretching and strength through a full range both added range in healthy knees. Our knee mobility routine puts it together in about 12 minutes.
Stairs and chairs need about 90 to 120 degrees, getting out of a bath about 135, and a deep squat with your heels up about 157. Compare your two knees rather than a chart, and get a big loss checked.
Rest your heel on a rolled towel with nothing under the knee and let it relax straight, then tighten the thigh to press the back of the knee down, and stretch your hamstrings. After surgery, follow our ACL or knee replacement guide's steps. A knee that is blocked from straightening after a twist needs checking.
Stretching trials gained range over a few weeks. After a knee replacement, most bend returns in the first 12 weeks and keeps improving for up to a year. People vary, so nobody can promise a number.
Usually, yes: exercise is a core treatment for knee arthritis, and stretching eased pain in trials. Range gains are small and less tested; about 4 to 6 degrees more bend is a change people notice.
Tell your team early: knees that stall in the first weeks tend to stay behind, and treatment worked best within about 3 months. Our knee replacement guide's threshold is about 90 degrees of bend by around 6 weeks.
Getting fully straight comes first, then the bend, at your team's pace. Our ACL surgery guide has the stages and the checks before running.
A few degrees past straight is common. Very bendy knees need strength and control rather than stretching; see a GP if they come with pain, sprains or joints that slip out.
Often swelling, a stiff thigh or scar tissue after surgery, and at full bend the thigh also meets the calf. A knee that locks, gives way or swells needs checking.
Not routinely: it added about 2 degrees across trials, and a 2026 US guideline recommends against it. Active heel slides did as well in a trial.
Only a little: about 3 to 5 degrees between younger adults and people aged 65 to 74 in a US survey. A bigger loss is worth getting checked.
Exercise education, not a personal prescription, and clinical review of these guides is pending. Check with a GP before starting hard training if you have a heart condition, chest pain, dizziness or breathlessness when active, and stop for sharp or increasing pain. Health disclaimer.
