Joint guide
A joint is where two bones meet. Most of the ones you move with, from your knuckles to your hips, are synovial joints: bone ends capped with smooth cartilage and sealed in a capsule of slippery fluid. Cartilage has no blood supply, so it is fed by that fluid, and the muscles around each joint hold it steady.
The honest headline is that exercise doesn't wear healthy joints out. Long-term exercise caused no harm in studies of painful knees, it is a core treatment for osteoarthritis, and small studies suggest that movement and load help keep cartilage healthy. Most joint myths, from running to cracking your knuckles, don't stand up to the evidence.
This guide explains how joints work and what every joint needs, weighs the evidence on running, knuckle cracking, the weather, supplements and lifting weights, and says when to get help. It links to a guide for each major joint, with a move for every joint and a joint care workout to follow.
A guide to each major joint: how it is built, how far it moves, what keeps it healthy and the moves to train it, with 3D demos.
The shoulder's four joints, the rotator cuff, why it trades stability for range, how the shoulder blade moves, normal ranges, and exercises to keep it strong.
Elbow jointThe elbow's three joints, how the forearm turns palm up and down, normal ranges and the carrying angle, what keeps it healthy, and exercises with 3D demos.
Wrist and handHow many bones are in the hand, the carpal tunnel, the thumb's saddle joint, how grip works, grip strength as a health marker, and wrist and hand exercises.
SpineHow your spine is built and moves: 33 vertebrae, 23 discs, the natural curves and normal ranges, plus the evidence on bending, lifting and cracking your back.
Hip jointHow the hip's ball and socket works: the labrum, ligaments and big muscles, normal ranges by age, the forces it takes, and what keeps hips strong and mobile.
Knee jointHow the knee works: four main ligaments, the menisci and kneecap, normal range, why knees crack, whether squats harm knees, and knees over toes, with evidence.
Ankle and footHow the ankle and foot work: 26 bones, 33 joints and three arches, normal ankle range, flat feet, barefoot shoes and foot strength, with the evidence and moves.
Most of the joints you move with are synovial joints. The bone ends are capped with smooth cartilage 2 to 4 mm thick and sealed in a capsule whose lining makes a slippery fluid. Cartilage has no blood vessels or nerves: it is fed by diffusion from that fluid, and the squeeze of everyday loading helps.
Take normal loading away and cartilage thins: by 10 to 16% within 6 months after a spinal cord injury, and by 3 to 7% in 7 weeks of partial weight-bearing after an ankle fracture. The studies are small, so we grade this emerging. Our editorial advice is to move every joint through its range every day.
In 49 studies of exercise lasting 3 to 30 months, adults with painful knees had no serious harms, no more pain and no faster damage on scans. NICE (the National Institute for Health and Care Excellence) makes exercise a core treatment for osteoarthritis. Exercise hasn't been shown to regrow cartilage that is already lost.
The muscles crossing a joint act like moving ligaments, most of all where the ligaments are weak, as at the shoulder. In 25 trials in sport, strength training cut injuries to about a third; stretching programmes made no difference.
Recreational runners have less hip and knee arthritis than people who don't run, the studies of knuckle cracking found no link with arthritis, rainy days don't send more people to the doctor with joint pain, and NICE advises against glucosamine.
Go to A&E or call 999 for very bad joint pain after a fall, a joint that has moved out of place, or a joint you can't put weight on. Get an urgent GP appointment or call NHS 111 for a hot, swollen joint, especially if you feel unwell or have a high temperature.
Anatomists sort joints by what holds the bones together, which also sets how much they move. Fibrous joints are joined by tough collagen and barely move, like the sutures between the bones of the skull and the teeth in their sockets. One exception, the sheet of tissue between the radius and ulna in the forearm, lets the radius turn.
Cartilaginous joints are joined by cartilage and move a little, like the pubic symphysis at the front of the pelvis and the discs between the vertebrae. Synovial joints move freely, and they are almost all the joints you move on purpose.
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Synovial joints are named by the movement their shape allows.
The bone ends are covered in articular cartilage, smooth hyaline cartilage 2 to 4 mm thick. It is 65 to 80% water, held in a mesh of collagen and water-binding molecules called proteoglycans, and its cells make up only about 2% of its volume.
A fibrous capsule seals the joint. Its thin lining, the synovial membrane, makes synovial fluid: a filtrate of blood plasma made slippery by hyaluronan and lubricin. The fluid lubricates the joint and, by diffusion, feeds the cartilage, the menisci of the knee and the labrum, the rim of cartilage that deepens the shoulder's socket.
Cartilage carries load through its water. Water is held tight in the matrix and moves through it only slowly, so under load the pressurised water carries much of the force; that is how cartilage copes with loads of several times body weight. Without blood vessels, its cells live mostly without oxygen and get their food by diffusion, which compression speeds up.
Its building blocks turn over very slowly: its proteoglycans can take up to 25 years, and its collagen lasts from decades to as long as 400 years. Its cells rarely divide. That is why damaged cartilage repairs slowly and poorly.
Ligaments join bone to bone and limit how far a joint can move. Bursae are small fluid-filled sacs that let tendons, muscle and skin glide over bone, such as the bursa under the point of the shoulder and the one over the point of the elbow.
Nerve endings in the capsule and ligaments tell your brain where the joint is (proprioception) and signal pain. Cartilage itself has no nerves, so pain from a joint comes from the tissues around it.
In the words of one anatomy reference, muscle strength directly correlates with joint stability, particularly in synovial joints. The muscles and tendons crossing a joint resist the forces on it like a moving ligament, which matters most during hard effort at joints with weaker ligaments, such as the shoulder.
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Range of motion is measured in degrees, usually with a goniometer, a protractor with arms. Published normal values vary: in 674 healthy people aged 2 to 69, the averages differed significantly from the most commonly used normal values in most cases, and 2,404 adults without shoulder pain averaged about 160 degrees of forward arm raise, short of the textbook 180. Treat any chart as a rough guide.
There is no single agreed number, because it depends on what you count: anatomists class the sutures of the skull and the teeth in their sockets as joints. How each kind moves matters more than the total.
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Reference texts agree: cartilage has no blood supply, its cells are fed by diffusion from the joint fluid, and the compressive forces that regularly act on it increase that diffusion. A review of cartilage science adds that joint motion and load maintain normal cartilage, and that inactivity degrades it.
The human evidence comes from small studies that agree. After a complete spinal cord injury, knee cartilage was 10 to 16% thinner than in healthy volunteers within 6 months, and up to 25% thinner at 2 years, with 6 to 11 people measured at each time point. In 20 people on partial weight-bearing after an ankle fracture, knee cartilage thinned by 3 to 7% in 7 weeks, while the other knee didn't change.
In a trial in 45 adults who had had part of a knee meniscus removed, 30 had both scans: 4 months of supervised exercise 3 times a week improved a marker of cartilage make-up (its glycosaminoglycan content) compared with no exercise, and the more active people became, the more it improved. Studies this small are why we grade the link emerging.
A review of 9 trials that scanned knee cartilage in people with, or at risk of, knee osteoarthritis found that knee-loading exercise didn't seem to harm it; most comparisons found no change in its thickness or volume. The quality of the evidence was low.
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Across 49 studies (48 of them randomised trials) of exercise lasting 3 to 30 months in adults with knee pain or osteoarthritis, average age over 45, there were no serious harms, no increase in pain, no loss of function, no faster progression on scans and no more knee replacements. NICE's guideline committee wanted to reassure people that exercise is not harmful to osteoarthritic joints.
NICE tells clinicians to offer therapeutic exercise to everyone with osteoarthritis, for example local muscle strengthening and general aerobic fitness, and to explain that joint pain may increase at first but that regular exercise will benefit the joints. The NHS adds a caution: follow your exercise plan, because doing too much too quickly, or the wrong sort of exercise, may damage your joints.
In 25 trials (26,610 people), strength training cut sports injuries to about a third, while stretching made no difference. A later review of 6 strength training trials (7,738 people aged 12 to 40) found much the same, and the more strength training people did, the lower their risk.
In 6,000 people aged 5 to 92, overall flexibility fell by about 0.6% a year in women and 0.8% in men, most at the shoulders and trunk and least at the elbows and knees, and women were more flexible at every age. Range is trainable: across 55 studies, strength training with a load improved range of motion as much as stretching, though training with body weight alone didn't.
Everyday life uses only part of a joint's range. In a study of 24 adults doing 24 daily activities, the hand's joints stayed 5 to 28 degrees short of their full range, and the authors suggest daily activities alone may not keep full range.
Our editorial advice: move every joint through its full range every day. The joint circles below take a few minutes; they are barely tested in trials, so treat them as a way to move each joint rather than a treatment. Lifting through a full range builds range too.
Strong muscles steady joints, strength training lowers injury risk, and NICE recommends local muscle strengthening for osteoarthritis. Our editorial starting point is 2 or 3 strength sessions a week that cover the whole body; the cartilage trial above used supervised exercise 3 times a week for 4 months.
NICE advises telling people with osteoarthritis that joint pain may increase when they start exercising, and that regular exercise will still benefit their joints. The NHS warns that doing too much too quickly may damage your joints. Our editorial rule: discomfort up to about 5 out of 10 that settles by the next day is fine for most joints (lower at the elbow, as our elbow pain guide explains), while sharp or worsening pain means scale back.
For people with osteoarthritis who are living with overweight, NICE says weight loss will improve quality of life and physical function and reduce pain: any amount is likely to help, and losing 10% of body weight is likely to be better than 5%. In 142 older adults with knee osteoarthritis, each kilogram lost took about 4 kg of force off the knee with each step, in an analysis of one trial.
For a painful joint, the NHS says to rest it if you can but not to stop moving it completely. Between hard sessions, plan easier days; our rest days guide covers recovery.
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Past injury stands out as a risk for later arthritis. In 117 former elite athletes, a previous knee injury raised the odds of knee osteoarthritis almost fivefold, and in 3,804 marathon runners, past hip or knee injury or surgery, age, BMI (body mass index) and family history predicted arthritis, while running history didn't. Strength training lowers injury risk, and an injured joint deserves a proper rehab plan (our advice).
In a UK questionnaire survey, 18.3% of 12,853 adults were hypermobile, and the link with pain was modest. The NHS says joint hypermobility syndrome usually affects children and young people and often gets better as you get older; a GP will usually check how flexible your joints are with the Beighton score, which our hypermobility guide explains.
The NHS says the main treatment for joint hypermobility syndrome is improving muscle strength and fitness so your joints are better protected. It suggests starting with low-impact exercise such as swimming or cycling if you haven't been active, because doing no exercise can make symptoms worse.
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Osteoarthritis is the most common type of arthritis and usually starts in the late 40s. It most often affects the knees, hips and small joints of the hands. As part of normal life your joints are exposed to a constant low level of damage, which your body usually repairs; in osteoarthritis, the protective cartilage on the ends of the bones breaks down. NICE's core treatments are therapeutic exercise and, where it applies, weight management, with information and support. Our arthritis guide has the detail.
Pain and stiffness on both sides of the body that is worse after not moving, such as when you wake up, can be rheumatoid arthritis, and the NHS advises seeing a GP if your joints are stiff for more than 30 minutes after waking. Our rheumatoid arthritis guide covers exercise for it.
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The NHS notes that perimenopause and menopause can cause aching and painful joints, because of lower levels of oestrogen. Our menopause guide covers exercise through that time.
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For pain in a particular joint, start with the pain guide for that area: each maps pain by where it hurts and has a staged exercise plan.
One for each joint, from the neck to the ankle. Move slowly through the range you can control, a few times in each direction, once or twice a day; each move's page gives its own dose.
3D demoNeck CARsBeginner · No equipment
3D demoShoulder CARs (controlled articular rotations)Beginner · No equipment
3D demoWrist & forearm flowBeginner · No equipment
3D demoTendon glides (hand tendon gliding exercises)Beginner · No equipment
3D demoCat-cowBeginner · No equipment
3D demoThoracic rotationBeginner · No equipment
3D demoStanding hip CARsBeginner · A wall
3D demoAnkle CARsBeginner · No equipmentStrength for the muscles around the hips, knees, ankles, shoulders, elbows and grip. Our starting point: 2 to 3 sets of 8 to 15 on 2 or 3 days a week, stopping short of sharp pain (each move's page gives its own dose).
3D demoSit to stand from a chairBeginner · A bench or box
3D demoBodyweight squatBeginner · No equipment
3D demoWall push-upBeginner · A wall
3D demoBand rowBeginner · A band + An anchor point
3D demoGlute bridgeBeginner · No equipment
3D demoBird dogBeginner · No equipment
3D demoSlow calf raiseBeginner · A wall
3D demoFarmer's carryBeginner · A dumbbell + A kettlebellThe joint care workout does both halves in 25 minutes. The daily mobility routine is joint circles and range only, and the arthritis routine is built for sore joints.
A 25-minute session for healthy joints: slow circles to take every joint through its range, then a strength circuit for hips, knees, ankles, shoulders and grip.
25 minBeginner13 movesA wall, A bench or boxA 12-minute routine to move every joint through its range under control: slow neck, shoulder, hip and ankle circles, spine and hip rotation, and deep squats.
12 minBeginner10 movesA wallA 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 20-minute full-body dumbbell workout: two supersets of squats, rows, Romanian deadlifts and push-ups. Twice a week covers the minimum dose.
20 minBeginner8 movesA dumbbell, A bench or boxA 40-minute strength and balance session for over-65s, built from the Otago home programme and NHS exercises, using a chair, a counter and a step.
40 minBeginner18 movesA bench or box, Something with weightA 25-minute low-load routine for hypermobile joints: hip, trunk and shoulder control plus balance, done slowly in the middle of your range.
25 minBeginner15 movesA bench or box, A wallIf you have very bad joint pain after a fall or injury, you can't walk or put weight on a joint, a joint has moved out of place, or you have tingling or no feeling around the joint after an injury.
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Chest pain that feels tight or like squeezing, chest pain spreading to your arms, neck or jaw, or severe difficulty breathing can be a heart attack. Shoulder or arm pain with these symptoms is an emergency, not a joint problem.
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If you have joint pain and the skin around it is swollen and feels hot, or joint pain and you feel generally unwell, have a high temperature or feel hot, cold or shivery. A joint infection (septic arthritis) usually develops quickly over a few days and needs checking straight away. In the US, contact your doctor or urgent care.
If joint pain is stopping you doing normal activities or affecting your sleep, the pain or swelling is getting worse or keeps coming back, it hasn't improved after 2 weeks of treating it at home, your joints are stiff for more than 30 minutes after waking up, or your child has joint problems. In many areas you can refer yourself to NHS physiotherapy through community musculoskeletal (MSK) services.
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See a GP if you think you or your child have joint hypermobility syndrome: for example, you keep getting pain and stiffness in your joints, sprains and strains, or joints that pop out, or you often feel tired even after rest.
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During exercise, stop for sharp or increasing pain, a feeling of a joint slipping out, or new tingling or numbness, and get it checked if it doesn't settle (our advice).
Not for most people. Across 25 studies (125,810 people), 3.5% of recreational runners had hip or knee osteoarthritis, against 10.2% of people who didn't run and 13.3% of competitive runners. The authors couldn't rule out other explanations, such as past injuries, so these are associations.
Other reviews point the same way: findings on osteoarthritis were mixed across 15 studies, weekly distance wasn't linked with knee osteoarthritis in 9 case-control studies (most at high risk of bias), and running didn't worsen knee symptoms or X-rays in the short term across 17 studies. In 3,804 marathon runners, past injury, age, BMI and family history predicted arthritis, not years or miles run. If you already have knee osteoarthritis, our arthritis guide covers running: in 1,203 people with it, those who ran didn't get worse.
The studies that have looked found no link, though they are small or simple. In a self-experiment (one person), a doctor cracked the knuckles of his left hand at least twice a day for 50 years, at least 36,500 times, and left the right alone; as Scientific American reported his words, there was no arthritis in either hand and no apparent difference between them. A 1975 survey of older nursing-home residents and a 1990 cross-sectional study of 300 patients aged 45 and over found no more hand arthritis in people who cracked their knuckles.
A 2011 case-control study of 215 adults aged 50 to 89 with hand X-rays found arthritis in 18.1% of crackers and 21.5% of non-crackers, with no link to how many years or how often people had cracked. None of these studies followed crackers and non-crackers forward for years (a prospective cohort study); we found none that has, and the authors of a 2017 study say long-term effects still need research.
The 1990 study of 300 patients found more hand swelling and weaker grip in habitual crackers. Newer studies didn't: a 2017 study in which blinded examiners checked 400 knuckles in 40 adults found no difference in hand function, looseness or grip, and no swelling at all, and a 2017 ultrasound study of 70 young adults found crackers' grip no weaker.
Real-time MRI (magnetic resonance imaging) of 10 knuckles showed a gas cavity forming in the joint fluid at the moment the joint surfaces separated and cracked, rather than a bubble collapsing, and ultrasound shows a bright flash in the joint as it cracks. Afterwards the joint moves a little further, and it typically takes at least 15 minutes before the same joint will crack again.
The release of a joint is a normal event that may or may not make a noise, and it happens in healthy joints; not every joint noise is a release. Sounds without pain or swelling are usually nothing to worry about. Clicking that comes with pain, swelling, locking, catching or a feeling of the joint slipping is different: the NHS lists a shoulder that feels like it is clicking or locking, with a tingling, numb or weak arm, as a possible sign of instability.
The evidence pulls both ways. In 1.55 million Medicare patients aged 65 and over (11.7 million visits to their doctors), visits for joint or back pain were no more common on rainy days than on dry ones, or in rainier weeks.
In a UK smartphone study, 2,658 volunteers with long-term pain, mostly arthritis, logged their pain for up to 15 months. More humid, windier and lower-pressure days went with more painful days, though rain and temperature didn't; the worst combination of weather raised the odds of a painful day by about 20% against an average day. The volunteers knew what was being studied, which the authors list as a limitation. A 2023 review of 14 osteoarthritis studies found 13 reported some link with weather, but they varied in which weather mattered and by how much.
Our reading: any effect is small. Keep moving on damp days; the NHS advises against completely stopping moving a sore joint.
NICE says not to offer glucosamine to manage osteoarthritis, because there is no strong evidence of benefit: the evidence was inconsistent, and the largest benefits came from smaller, lower-quality studies. GPs no longer prescribe glucosamine or chondroitin on the NHS.
In 10 large trials (3,803 people with hip or knee osteoarthritis), glucosamine, chondroitin or both eased pain by 0.3 to 0.5 cm on a 10 cm scale compared with a placebo, less than the 0.9 cm the researchers set as the smallest difference that matters, and didn't slow the narrowing of the joint space. Trials not funded by industry found smaller effects.
Across 69 trials of 20 supplements, a few, such as collagen hydrolysate, curcumin and Boswellia, showed large short-term effects on pain in small trials of very low quality, but none had a clinically important effect in the long term, and glucosamine and chondroitin were either ineffective or had small effects of doubtful importance. NICE also advises against hyaluronan (gel) injections into arthritic joints. Exercise and, if you need it, weight loss are the treatments with the best evidence.
The direct evidence is thin, so we grade this mixed. The reassurance is extrapolated from other kinds of study: in trials of sports injuries, strength training cut injuries to about a third; the weight-training sports, such as weightlifting, powerlifting and bodybuilding, have relatively low injury rates compared with common team sports; and long-term exercise didn't harm painful knees.
The caveats: in a small study of former elite athletes aged 45 to 68, 31% of 29 weightlifters had knee osteoarthritis on X-ray against 3% of 29 shooters, explained partly by the weightlifters' high body weight. Across 80 studies, jobs with heavy lifting, kneeling and squatting were linked with more knee osteoarthritis. Our reading: build load gradually and lift with control, rather than avoiding lifting.
The NHS describes joints as exposed to a constant low level of damage that the body usually repairs. Long-term exercise studies found no faster damage on scans and no more knee replacements, and NICE's committee wanted to reassure people that exercise is not harmful to osteoarthritic joints.
In 9 trials that scanned knee cartilage, exercise mostly made no difference to its thickness or volume. One small trial found it improved the cartilage's make-up, which is encouraging, but there is no good evidence that exercise regrows cartilage that is lost, and cartilage repairs itself poorly. Regular exercise eases pain and improves function for as long as you keep it up.
A joint is where two bones meet. Fibrous joints, like the sutures of the skull, barely move; cartilaginous joints, like the discs in your spine, move a little; and synovial joints move freely. Synovial joints come in six shapes: hinge, pivot, condyloid, saddle, plane and ball-and-socket.
A freely moving joint where the bone ends are capped with smooth cartilage and sealed in a fluid-filled capsule. The capsule's lining makes synovial fluid, which lubricates the joint and feeds the cartilage. The shoulder, elbow, wrist, hip, knee and finger joints are all synovial joints.
Joint cartilage is a smooth layer 2 to 4 mm thick, mostly water held in a mesh of collagen and proteoglycans, with no blood supply or nerves. Its cells rarely divide, so it repairs itself slowly and poorly. Exercise hasn't been shown to regrow lost cartilage, though it doesn't harm it and it eases arthritis pain.
Probably, though the evidence is small. Cartilage is fed by diffusion from the joint fluid, loading helps that, and it thinned in small studies of people who couldn't load their legs normally. In one small trial, exercise improved cartilage make-up, and a review of 9 trials found knee-loading exercise didn't harm it.
Move every joint through its full range, ideally every day, strengthen the muscles around your joints 2 or 3 times a week, build up new activities gradually and keep to a healthy weight. Range falls with age, most at the shoulders, but strength training through a full range and stretching both build it back.
Pulling a joint apart drops the pressure inside it until a gas cavity forms in the joint fluid with a pop, which is why the same knuckle won't crack again for at least 15 minutes. Not every joint noise is this kind of release. Sounds without pain or swelling are usually harmless; clicking with pain, swelling, locking or a feeling of slipping should be checked.
It hasn't been linked with arthritis: a 1990 study of 300 patients and a 2011 study of 215 adults with hand X-rays found no link, and one doctor who cracked only his left hand for 50 years had no arthritis in either hand. One 1990 study found more hand swelling and weaker grip in crackers, but newer studies didn't. No study has followed crackers for years, so the evidence is reassuring rather than final.
Not for most people. Across 25 studies, recreational runners had less hip and knee arthritis than people who didn't run (3.5% against 10.2%), and in marathon runners, past injuries, age, weight and family history mattered more than miles. If you already have knee arthritis, our arthritis guide covers running.
The evidence is mixed. Rain made no difference to doctor visits for joint pain across 11.7 million visits, but in a UK smartphone study of 2,658 volunteers with long-term pain, humid, windy, low-pressure days raised the odds of a painful day by up to about 20%. Any effect is small, so keep moving on damp days.
NICE advises against offering glucosamine for osteoarthritis because there is no strong evidence that it helps, and GPs no longer prescribe glucosamine or chondroitin. In large trials, the pain relief was smaller than the difference that matters to patients, and no supplement has shown a meaningful long-term effect. Exercise and, if needed, weight loss have the best evidence.
Not for most people, though the reassurance is indirect: strength training cut sports injuries to about a third in 25 trials, and exercise is a core treatment for arthritic joints. Decades of elite weightlifting at a high body weight, and jobs with heavy lifting and kneeling, are linked with more knee arthritis, so build load gradually.
There's no single agreed number, because it depends on what you count: anatomists class the sutures of the skull and the teeth in their sockets as joints. How each kind of joint moves matters more than the total, and our joint guides cover the major ones.
Education about how your joints work, not a diagnosis, and clinical review of these guides is pending. For a painful, swollen or injured joint, see the pain guide for that area and a doctor or physiotherapist, and stop any exercise that causes sharp or increasing pain. Health disclaimer.
