Exercise for Knee Arthritis: What Helps, What Hurts and How Much

Exercise is one of the most effective treatments for knee arthritis: strengthening the thigh muscles and doing regular low-impact activity reduces pain and improves how the knee works. NICE recommends it for everyone with knee osteoarthritis as a core treatment¹. It will not regrow worn cartilage, but stronger muscles absorb and steady the load that would otherwise go straight through the joint, and that is often the difference between a knee that runs your life and one you can work around.

I lived with osteoarthritis in my knees for the best part of a decade before I had my left one replaced in my early sixties. For a good part of that time I exercised in fits and starts: keen for a month after a physiotherapy appointment, then a flare would frighten me off and I would stop for the whole winter. The weeks I kept it up were the weeks my knee was best, and I only properly understood that afterwards. This guide, checked by a consultant orthopaedic surgeon, is the version I wish I had pinned to the fridge: what to do, how much, how to tell useful soreness from a warning, and what to go easy on.

Why exercise helps a worn knee

Exercise helps because the muscles around the knee are its shock absorbers, and in arthritis they are usually weaker than they should be. Pain makes you move less, moving less weakens the thigh muscles, and weaker muscles leave more of each step to be taken by the joint itself. Strengthening breaks that cycle. Regular movement also keeps the knee from stiffening and helps the cartilage that is left, which relies on movement to stay nourished².

This matters to a lot of people. Around 1 in 5 adults over the age of 45 have osteoarthritis in the knee², and NICE is clear that exercise is a core treatment for all of them, regardless of age, weight, other health conditions or how severe the changes on an X-ray look¹. It sits alongside weight management and information about the condition as the foundation that everything else, from painkillers to injections, is added on top of. Our guide to the alternatives to knee replacement puts exercise in context with those other options.

Strengthening: the exercises that earn their place

Strengthening is the heart of it, and the thigh muscles (the quadriceps at the front and the hamstrings at the back) matter most, followed by the hip muscles that control how the knee lines up. The World Health Organization recommends muscle-strengthening activity on 2 or more days a week for adults³, and for an arthritic knee that is a sensible minimum. Most physiotherapy programmes for knee osteoarthritis are built from a handful of simple moves:

• Static quadriceps: sitting with the leg straight, tighten the thigh to press the back of the knee down, hold for about 5 seconds and relax.
• Straight-leg raise: lying or sitting, lock the knee straight and lift the leg a short way, then lower it slowly.
• Sit-to-stand: rise from a firm chair without using your hands if you can, and sit back down slowly. A higher chair makes it easier.
• Step-ups: step up onto the bottom stair with the weaker leg leading, then down again, holding the banister.
• Side-lying leg lifts or a resistance band around the knees: to strengthen the hip muscles that keep the knee from collapsing inwards.

Start with 1 set of about 8 to 10 slow repetitions and build towards 2 or 3 sets over a few weeks. Slow and controlled beats fast and many. Once the easy versions feel easy, a physiotherapist can add ankle weights, bands or gym equipment. A tailored, supervised programme is something NICE suggests considering, especially at the start¹, because a professional can adjust it to which part of your knee is worn and how it behaves.

These overlap with the prehab exercises in our guide to knee replacement exercises, and that is no coincidence: the same strength that eases arthritis now will make any later recovery easier.

Aerobic activity: keep moving, gently

The second pillar is regular activity that raises your heart rate without pounding the joint. The WHO recommends 150 to 300 minutes of moderate activity a week for adults, which works out at roughly 20 to 40 minutes a day³. With a sore knee that can sound like a lot, so treat it as a direction of travel rather than a starting point. Ten minutes twice a day counts.

The activities that tend to suit arthritic knees are:

• Walking: free and adaptable. Cushioned shoes, flatter routes and a stick in the opposite hand on bad days all help.
• Cycling: a static bike at home or in a gym moves the knee through a range with little impact. Set the saddle high enough that the knee does not bend too far at the top of the stroke.
• Swimming and water exercise: the water supports your weight, which lets a painful knee move more freely. Breaststroke kick can irritate some knees, so a front crawl kick or aqua aerobics may suit better.
• Cross-trainer: an option once your knee will tolerate it.

For adults over 65 with poor mobility, the WHO also recommends activity that improves balance and helps prevent falls on 3 or more days a week³, and an arthritic knee that sometimes gives way makes that advice especially relevant.

How much pain is acceptable

Some discomfort during exercise is expected and is not a sign you are wearing the knee out faster. This was the single thing I most needed to hear and did not. Arthritic knees often ache when you start using them more, and NICE advises that people with osteoarthritis should be given information and support to keep exercising, because the benefit comes from doing it consistently over months¹.

A rule of thumb that many physiotherapists use: mild to moderate pain during exercise is acceptable if it settles back to your usual level by the next morning. If the knee is clearly worse the following day, noticeably more swollen, or you are limping more, the dose was too high. Cut the repetitions, the distance or the depth of the bend, and build up again more slowly. That is adjusting, not failing, and it is very different from stopping.

The signs that are not exercise soreness are a knee that becomes hot, red and very swollen, locks so it will not straighten, or gives way badly. Those need a doctor’s opinion promptly rather than a modified routine.

Weight and exercise work together

Exercise does far more for an arthritic knee when it comes with weight loss, if you are carrying extra weight. The load through the knee is several times your body weight when you walk and climb stairs, so each kilogram lost is felt in every step⁴. NICE advises that any amount of weight loss is likely to help, but that losing 10% of body weight is likely to be better than losing 5%¹.

Exercise on its own is not a very efficient way to lose weight, and I would not want anyone to feel they have failed because the scales barely moved after a month of walking. The two do different jobs: diet shifts the weight, exercise builds the muscle that protects the joint and makes the weight loss easier to keep. Our article on losing weight before knee surgery goes into how to approach it safely.

What to go easy on

Very few activities are completely off limits with knee arthritis, but some are harder on a worn joint and tend to cause flares⁴. The usual culprits are:

• Deep squats and lunges: they load the front of the knee heavily. Shallow versions, such as sit-to-stand from a chair, give much of the benefit.
• Kneeling: often painful on an arthritic knee. A cushioned kneeler helps in the garden.
• High-impact and twisting sport: running on hard surfaces, jumping, squash and football tend to aggravate an already painful knee, though some people with milder arthritis carry on running comfortably. Let the next-day response be your guide.
• Long descents: coming downhill or downstairs loads the knee more than going up. Walking poles on hills and a banister at home take some of it.

The goal is not to wrap the knee in cotton wool. It is to find the most activity the knee will tolerate and do that regularly, swapping the things that flare it for gentler versions rather than dropping them altogether.

When exercise stops being enough

Exercise eases symptoms and can delay surgery for years, but it cannot reverse the wear, and there can come a point where it no longer keeps pain and stiffness at a level you can live with. That is not a sign you did it wrong. When pain wrecks your sleep, limits how far you can walk and resists exercise, weight management and pain relief, NICE recommends referral to consider joint replacement¹. Our guide to the signs you need a knee replacement covers how to judge it.

If you do reach that point, the exercise will not have been wasted. A knee replacement is a successful operation, with around 90 to 95% of implants still in place at 10 years and most lasting 15 to 20 years or more⁵, but the recovery is demanding and the stronger your leg going in, the easier the first weeks are. I did very little in the months right before my operation and paid for it on the ward. Looking back over the whole decade, the best years my knees had were the years I kept moving, and if I could tell my younger self one thing it would be to stop treating exercise as a course of treatment and start treating it as part of the week.