How to strengthen your knees: the muscles that support them, the exercises that work, how often, and when knee pain needs a different plan

Strengthen the muscles round the knee

The quadriceps, hamstrings, glutes and side hip muscles, and calves move and steady your knee. For sport, balance and landing practice are the other half.

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Exercise helps sore knees, modestly

In 139 trials of knee arthritis, exercise eased pain by about 13 points on a 100-point scale compared with no treatment, and NICE recommends muscle-strengthening exercise for everyone with osteoarthritis. For kneecap pain, hip and knee exercises together beat knee exercises alone.

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The quadriceps matter most, but not alone

Programmes focused on the quadriceps eased more arthritis pain than general leg programmes, and weaker thigh muscles go with knee arthritis later (a link, not proof). Add hamstring, side hip and calf work.

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Five kinds of move, 2 or 3 times a week

A squat or leg press, a single-leg move such as step-ups or split squats, a hamstring move, side hip work and calf raises: 2 or 3 sets of 8 to 15, stopping 2 or 3 reps short of failure, as our plans advise.

You don't need heavy weights for painful knees

In 377 adults with knee arthritis, heavy strength training eased pain no more than lighter training over 18 months, and strength has to rise a lot before pain changes. Give it months, within our knee pain rule.

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Squats are fine for healthy knees

Squat as deep as you can with control and without pain, and let your knees travel past your toes: blocking them shifts the load to your hips and lower back, as our squat guide explains.

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Muscles, not the joint

A 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. You can't strengthen the joint itself; you strengthen the muscles that move and steady it, and the tendons and bone adapt with them.

The quadriceps

The four muscles at the front of your thigh straighten the knee and control it as you sit down, squat, land and go downstairs. They are the muscles most linked with knee arthritis and kneecap pain.

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The hamstrings, glutes and calves

The hamstrings bend the knee and share the load with the knee's ligaments. The glutes and side hip muscles keep the knee in line over your foot as you step, land and stand on one leg. One of the calf muscles crosses the back of the knee too.

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Three reasons people search, one plan

Some want knees that cope with sport and stairs, some are getting older, and some have a knee that aches. The training is the same core; what changes is the depth, the load and the pain rule. A knee that hurts belongs first with its pain guide (see "When your knee hurts" below).

How people differ

Long thighs or stiff ankles mean more forward lean or more knee travel in a squat, which is normal. If you're heavier, body-weight moves are already a real load, so sit-to-stands and step-ups are a good start (our suggestion). Beginners get stronger within weeks, but painful knees take months to change.

Exercise eases knee arthritis, modestlyStrong evidence

In a 2024 Cochrane review of 139 trials and 12,468 people, exercise improved pain by about 13 points and function by about 12.5 points on 100-point scales compared with no treatment or usual care, straight after the programme (low and moderate certainty). No type of exercise beat another. The authors call the size of the benefit of uncertain clinical importance, partly because people knew which treatment they had.

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Guidelines put exercise firstStrong evidence

NICE recommends therapeutic exercise for everyone with osteoarthritis, such as local muscle strengthening and general aerobic fitness, and warns that joint pain may rise at first while regular exercise still helps the joint. OARSI makes structured exercise a core treatment for knee osteoarthritis, and the NHS calls exercise one of the most important treatments.

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Quadriceps work, about 3 times a weekEmerging evidence

Across 48 knee arthritis trials, aerobic, strength and functional exercise eased pain by similar amounts. Programmes focused on the quadriceps eased more pain than general leg programmes, and supervised exercise at least 3 times a week did better than less often. These are comparisons between trials, not head-to-head tests.

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More strength isn't automatically less painMixed evidence

In 45 trials of 4,699 people, strength programmes built more thigh strength than other exercise but didn't ease more pain; the authors estimate strength has to rise by about 30 to 40% before pain likely changes. In the START trial of 377 adults aged 50 and over, heavy strength training was no better for knee pain at 18 months than lighter training or an attention control.

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Weak thighs and later arthritisEmerging evidence

In 11 cohort studies of 46,819 people followed for at least 2 years, weaker thigh muscles went with higher odds of painful knee arthritis later, in women (1.85 times) and men (1.43 times). The evidence is low quality and shows a link, not that strengthening prevents arthritis.

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Kneecap pain: hip and knee exercise togetherStrong evidence

An international consensus recommends exercise for kneecap (patellofemoral) pain, combining hip and knee exercises in preference to knee exercises alone. In the Cochrane review of 31 trials, exercise cut pain during activity by about 1.5 points out of 10 (very low-quality but consistent evidence). In 14 trials of 673 people, hip and knee strengthening cut pain by 1.5 points out of 10 more than knee strengthening alone, without a measurable strength gain.

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What predicts kneecap painEmerging evidence

In 18 studies that followed 4,818 people, weak quadriceps predicted kneecap pain in military recruits. Weak hips didn't, and nor did age, height, weight or body mass index.

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Injury prevention in sportStrong evidence

Warm-ups that combine strength, balance and landing work cut ACL (anterior cruciate ligament, a major knee ligament) injuries by about 40% in 13 studies and by half when 8 meta-analyses were pooled, and non-contact ACL injuries in female athletes by about two-thirds; there's too little data in men to say. Across 25 trials of 26,610 people, strength training cut sports injuries to under a third, while stretching did nothing. The FIFA 11+ warm-up cut football injuries by 39%.

Sources 2, 16, 17, 18, 19

Recreational running and arthritisEmerging evidence

In 25 studies of 125,810 people, 3.5% of recreational runners had hip or knee arthritis, against 10.2% of non-runners and 13.3% of competitive runners. These are links that can't prove cause.

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The five kinds of move

A squat or leg press for the quadriceps; a single-leg move (step-ups, split squats, reverse lunges or step-downs); a hamstring move (Romanian deadlifts, leg curls, slider curls or Nordic curls); side hip work (lateral band walks, side-lying leg raises or clamshells); and calf and shin work (calf raises and tibialis raises). For sport, add landings and one-leg balance. This is our editorial grouping, matching our knee strengthening workout and bigger legs guide.

How often

Two or three sessions a week on days that aren't back to back. The NHS asks for strength work on at least 2 days a week, and in knee arthritis trials, 3 supervised sessions a week did better than fewer.

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Sets, reps and effort

Two or three sets of 8 to 15 per move (our editorial starting point). Stop squats, split squats and hinges 2 or 3 reps short of failure, and the last set of leg extensions, curls and calf raises 0 to 2 reps short, as our plans advise. In your first two weeks, stop every set with 3 or 4 reps to spare.

Rest

Two to 3 minutes between heavy squat sets, 90 seconds to 2 minutes for single-leg work, and 60 to 90 seconds for curls, extensions and calf raises, as our plans' notes say.

How deep

As deep as you can with control and without pain, as our bigger legs guide says. With kneecap pain, start with squats to about 45 degrees of knee bend and deepen them as the pain allows, as our squat guide explains. With sore knees, add depth before you add load.

Our knee pain rule

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.

Arthritis: pain may rise at first

NICE says joint pain may increase when you start exercising with osteoarthritis, and that regular exercise still helps your joints. Build up gradually, within the rule above, and see our knee arthritis guide.

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Knees past your toes is normalEmerging evidence

In 7 weight-trained men, stopping the knees from passing the toes lowered the load on the knee but moved it to the hips and lower back, so the authors concluded the knees may need to move a little past the toes. What matters is that your knees follow your toes rather than caving in, as our squat guide explains.

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Squats and healthy kneesEmerging evidence

The evidence is biomechanical reviews, with no outcome trials. One found the parallel squat wasn't harmful to healthy knees and could improve their stability; the other found no evidence that deep squats raise the risk to the knee's passive tissues when technique is learned and loads build gradually. They disagree on depth: the older review prefers parallel squats for athletes, the newer one says the stress behind the kneecap peaks at about a right angle, not deeper.

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With a sore knee

Change the depth and the load within our knee pain rule rather than dropping the move: squats to about 45 degrees of knee bend load the kneecap least, as our squat guide says, and the leg press lets you control the depth.

Add landings and balanceStrong evidence

The warm-ups that protect knees combine strength, balance and landing practice. In 1,892 girls aged 13 to 17, the FIFA 11+ warm-up lowered the risk of injuries overall and of severe injuries over a season. Our knee control warm-up builds this into 10 minutes before training.

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Running

Recreational running isn't linked with more knee arthritis. Two short strength sessions a week, as in our strength training plan for runners, cover the knee's muscles; build your running up gradually, and see our knee pain when running guide if a knee aches.

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Kneecap pain

Pain around or behind the kneecap with stairs, squats or sitting: our runner's knee guide has a staged plan with hip and knee exercises.

Knee arthritis

Exercise is a first-line treatment. Our knee arthritis guide and exercise for arthritis guide give the plans, and say how to handle pain that rises when you start.

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Pain at one point below or above the kneecap

Often a tendon. Our jumper's knee and quadriceps tendinopathy guides keep tendon pain to 3 out of 10 or less with a loading plan.

A twist, catching, locking or giving way

Our meniscus tear and ACL injury guides cover these, and the warning signs below say when to get it checked first. After surgery, follow your surgical team's limits and our ACL surgery or knee replacement guide.

Weeks for strength, months for sore knees

Strength rises within 2 to 6 weeks, as our get stronger guide explains, but the arthritis trials suggest strength has to rise a lot before pain changes, and the changes are modest. Treat 12 weeks as your first block (our editorial starting point) and keep going.

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After knee surgery

Follow your surgical team's limits. Our knee replacement, hip replacement and ACL (anterior cruciate ligament) injury guides cover the stages.

Older adults

Start with sit-to-stands, step-ups and leg extensions, and add balance work: strength and balance training together cut falls by about a third in older adults. The NHS asks adults 65 and over for strength, balance and flexibility work on at least 2 days a week.

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Osteoporosis

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.

Children and teenagers

A knee that hurts below the kneecap in a growing child can be Osgood-Schlatter disease: see our guide. Our children's exercise guide covers strength training for young people.

A pop with fast swelling: go 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.

Get advice from NHS 111 now

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: 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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A possible broken bone

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 possible torn knee tendon

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.

A clot in the leg

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).

See a GP

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.

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Stop and get medical help

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.

Call 999 (911 in the US)

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.

Ask for an urgent GP appointment or call NHS 111

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.

During any session

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.

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.

Check first

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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Hernia

See a GP if you think you have a hernia, a bulge or lump that may get bigger when you strain and smaller when you lie down. Get help from NHS 111 if you have a hernia and pain in or around it, a bloated tummy, you feel or are sick, you're vomiting blood or your vomit looks like coffee grounds, you're constipated, you have a high temperature or feel hot, cold or shivery, or you've suddenly become confused. Call 999 or go to A&E for a femoral hernia (a small lump at the top of your thigh, in your groin) with very bad tummy pain, sickness, being unable to fart or poo, a high temperature or sudden confusion.

"Squats and lunges are bad for your knees"Emerging evidence

Reviews of the biomechanics found no evidence that squats harm healthy knees, though they are reviews rather than outcome trials and disagree on the best depth. Squats and split squats are part of the programmes that ease knee arthritis and kneecap pain. With a sore knee, change the depth and load rather than dropping them.

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"Never let your knees go past your toes"Emerging evidence

Stopping the knees moved the load to the hips and lower back in a lab study. The NHS's own mini-squat tells you to aim your knees over your big toe. With kneecap pain, limit it for a while, then build it back.

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"If your knee hurts, rest it until it stops"Strong evidence

For knee arthritis and kneecap pain, exercise is a first-line treatment, and NICE says pain may rise at first without that meaning harm. Use our pain rule, and the warning signs above for the exceptions.

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"Heavier is better for bad knees"Emerging evidence

Heavy strength training eased knee arthritis pain no more than lighter training over 18 months in 377 adults. Choose loads by effort and pain, not a target weight.

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"Running wears out your knees"Emerging evidence

Recreational runners had less hip and knee arthritis than non-runners in observational studies, though competitive runners had more.

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"You need special inner-thigh (VMO) exercises"Mixed evidence

We found no trial support for isolating one part of the quadriceps. The kneecap pain consensus recommends hip and knee exercise together, and that combination eased pain without a measurable change in strength, so exercise seems to help in more ways than one muscle getting bigger (our reading).

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