Knee osteoarthritis: can you still exercise?

Knee osteoarthritis: a common condition, often misunderstood

Knee osteoarthritis, or gonarthrosis, affects roughly 10% of people over the age of 55. The cartilage covering the joint surfaces wears down progressively, the underlying bone changes shape, the synovial membrane becomes irritated. The knee swells, cracks and hurts on stairs. Imaging shows joint space narrowing and osteophytes (bony spurs).

Faced with this diagnosis, many patients hear the same message: "You have arthritis, you need to protect your knee." This well-meaning advice leads them to reduce physical activity. They stop running, hiking, playing tennis. They walk less. They take the lift instead of the stairs. They sit more.

That is a mistake. The most recent international guidelines, published by OARSI (Osteoarthritis Research Society International), EULAR (European League Against Rheumatism) and the ACR (American College of Rheumatology), agree: exercise is the first-line treatment for knee osteoarthritis. Before medication. Before injections. Before a joint replacement.

Why exercise is the primary treatment for osteoarthritis

Osteoarthritis is not simple mechanical wear. It is an active biological process in which inflammation, mechanical load, metabolic factors and the nervous system interact. Exercise acts on each of these factors.

Strengthening increases the muscles' capacity to absorb shock. The quadriceps, the main thigh muscle, is the knee's natural shock absorber. When it is strong, every step places less stress on the cartilage. Studies show that 12 weeks of quadriceps strengthening reduces osteoarthritic pain by 30 to 40%, a result comparable to anti-inflammatory drugs, without the side effects.

Movement stimulates the production of synovial fluid, the joint's natural lubricant. A knee that does not move stiffens and dehydrates. Cartilage, which feeds by imbibition (it absorbs nutrients like a sponge when compressed and released), depends on movement to survive. Immobility accelerates its breakdown.

Aerobic exercise reduces systemic inflammation. Osteoarthritis is accompanied by a chronic low-grade inflammatory state that maintains pain and disease progression. Regular physical activity lowers circulating inflammatory markers and improves the metabolic profile, slowing the advance of the condition.

Finally, exercise modulates pain at the central nervous system level. People with chronic osteoarthritis often have a lowered pain threshold (central sensitisation). Regular exercise recalibrates those circuits and reduces hypersensitivity.

What the research says about sport and knee osteoarthritis

A 2015 Cochrane review, updated in 2022, pooling 54 randomised controlled trials and more than 8,000 participants, concludes that therapeutic exercise reduces pain and improves physical function in people with knee osteoarthritis. The effect is moderate to large, comparable to oral anti-inflammatory drugs, and superior to passive treatments such as ultrasound or electrical stimulation.

A Norwegian study published in the BMJ in 2018 followed 140 patients with moderate to severe knee osteoarthritis. Participants were assigned to either a 12-week supervised exercise programme or a control group. At the end of the study, one-third of patients in the exercise group cancelled or postponed their joint replacement surgery, judging their condition had improved sufficiently. At the 2-year follow-up, the benefit was maintained.

Contrary to a widespread belief, moderate exercise does not damage cartilage. MRI studies show that regular physical activity does not reduce cartilage thickness in people with osteoarthritis. Some data even suggest a protective effect, probably linked to improved synovial fluid quality and maintained joint mechanics.

Recommended activities

Cycling

Cycling is often the first activity recommended by rheumatologists and physiotherapists. The seated position unloads the knee from body weight. The repetitive pedalling motion moves the joint through a comfortable range without impact. A stationary bike offers perfect resistance control and eliminates the risk of falling.

Set the saddle high enough so the knee does not bend beyond 90 degrees at the bottom of the pedal stroke. Start with light resistance and a duration of 15 to 20 minutes. Build up gradually. 30 to 45 minutes of cycling, 3 to 5 times per week, constitutes an effective programme.

Walking

Walking is a natural exercise that combines cardiovascular benefits, light muscular strengthening and joint mobilisation. It is not contraindicated in knee osteoarthritis, provided you respect pain signals. Favour flat, even terrain. Wear shoes with good cushioning. Start with a duration your knee tolerates and add 5 minutes per week.

If flat walking causes little pain but uphills and downhills are tough, stick to flat ground until strengthening improves your tolerance. Walking poles transfer some of the load to the arms and reduce knee pressure by 15 to 20%.

Swimming and aqua aerobics

Water supports the body and reduces joint loading by 50 to 90% depending on depth. Water resistance provides gentle, continuous muscular strengthening. Warm water (28 to 32 degrees Celsius) relaxes muscles and directly reduces pain.

Breaststroke is the one style to avoid: the scissor kick places a twisting load on the knee that can irritate an arthritic joint. Front crawl, backstroke and kicking with a board are better tolerated.

Strength training

A targeted strengthening programme is the cornerstone of gonarthrosis management. Exercises should target the quadriceps, hamstrings, gluteal muscles and calves. The knee is a hinge joint, but its stability depends on the entire muscular chain of the leg.

Seated knee extensions. Sit on a chair and straighten the leg slowly to horizontal. Hold 5 seconds. Lower over 3 seconds. 3 sets of 12 repetitions. Add an ankle weight when the exercise becomes easy.

Partial squats (half squats). Stand with feet shoulder-width apart. Bend the knees to a maximum of 45 degrees (not beyond 90). Keep the weight on the heels. Stand back up. 3 sets of 10. If flexion is painful, reduce the range. The exercise remains beneficial even with limited flexion.

Step-ups. Step onto a step with the affected leg. Control the descent with the same leg. 3 sets of 10 per leg. Step height determines intensity: start with a low step (15 cm) and increase progressively.

Glute bridge. Lie on your back, knees bent, feet on the floor. Lift the pelvis until the body forms a straight line from shoulders to knees. Hold 5 seconds. Lower. 3 sets of 12. The gluteus maximus is a major knee stabiliser. Its weakness causes dynamic valgus (the knee drifting inward), which increases pressure on the inner compartment of the joint.

Activities to adapt or avoid

Running

The question of running still divides professionals. Recent data are reassuring, however. A 2017 meta-analysis published in the Journal of Orthopaedic & Sports Physical Therapy showed that recreational runners did not have a higher risk of knee osteoarthritis compared with sedentary individuals. The risk was elevated only in elite runners with very high training volumes.

If you were running before osteoarthritis appeared and your knee tolerates it (no swelling, no increased pain the next day), it is reasonable to continue while adjusting volume. Reduce frequency (2 to 3 sessions per week at most), duration and intensity. Run on soft surfaces (trails, dirt paths) rather than asphalt. Alternate with low-impact activities (cycling, swimming) to maintain fitness without overloading the knee at every session.

If you have never run and your osteoarthritis is moderate to severe, running is probably not the best activity to start with. Cycling or aqua aerobics offer similar cardiovascular benefits with less joint stress.

Team and racquet sports

Tennis, football, basketball and handball involve rapid direction changes, accelerations, decelerations and sometimes collisions. These demands are high for an arthritic knee. This does not mean you must stop, but you need to adapt. Reduce playing time. Accept a less intense pace. Strengthen the muscles around the knee to compensate for cartilage loss. If the knee swells consistently after a session, that is a clear signal the load is too high.

Deep-knee-bend exercises

Full squats, prolonged crouching, wall sits at 90 degrees, leg press through a large range: these movements compress the cartilage heavily, especially the kneecap. Limit flexion to a comfortable angle, often between 30 and 60 degrees for an arthritic knee. Partial exercise is just as effective for building muscle, with far less joint stress.

The role of body weight

Every extra kilogram of body weight translates into 4 kilograms of additional force on the knee with every step. For a person carrying 10 kg of excess weight, that is 40 kg of extra pressure on the knee per stride. Multiplied by the 6,000 to 10,000 steps taken daily, the cumulative overload is substantial.

Studies show that a weight loss of 5 to 10% of body weight reduces osteoarthritic pain by an average of 50%. Exercise contributes to weight management, but diet remains the primary lever. The combination of exercise and weight management is the most effective non-surgical strategy for knee osteoarthritis.

Supplements and associated treatments

Glucosamine and chondroitin are among the best-selling supplements for osteoarthritis. Study results are mixed. Some indicate a slight benefit on pain, others find no difference compared with placebo. Current guidelines list them as an option, without strong endorsement. They are in no way a substitute for exercise.

Corticosteroid injections reduce pain and inflammation in the short term (4 to 8 weeks) but do not alter the course of osteoarthritis. Repeated use is discouraged because of a possible detrimental effect on cartilage. Hyaluronic acid injections (viscosupplementation) show variable results across studies.

A knee replacement remains a last resort, indicated when osteoarthritis is severe, pain is disabling and conservative treatments (exercise, weight loss, medication) have been exhausted. It is a reliable operation with a high satisfaction rate, but it is not without risks and itself requires demanding rehabilitation. Delaying replacement through exercise is a realistic goal for the majority of patients.

Building your programme: practical tips

A good programme for an arthritic knee combines three components: strengthening (2 to 3 sessions per week), aerobic exercise (3 to 5 sessions of 30 minutes) and mobility work (gentle daily stretches).

Start gently. In the first week, do less than you think you can. Assess the knee's response the next day. No swelling, no increase in baseline pain: you can raise the bar slightly the following week. Swelling or a pain increase lasting more than 24 hours signals that you have exceeded the knee's current capacity.

Warming up is non-negotiable. 5 to 10 minutes of cycling or walking before each strengthening session prepares the joint and improves synovial lubrication.

After exercise, if the knee feels warm, apply ice for 15 minutes. It is a simple way to limit the post-exercise inflammatory response.

Osteoarthritis fluctuates. Some weeks are good, others less so. Do not lose heart during flare-ups. Lower the intensity without stopping entirely. A complete stop restarts the deconditioning cycle and makes resumption harder.

You have every right to exercise with an arthritic knee. More than that: you need to exercise with an arthritic knee. Your cartilage will not crumble because you get on a bike or walk for 30 minutes. On the contrary, movement is what keeps it functional for as long as possible. Adapt the activity, respect the pain, progress at your own pace. And do not listen to anyone who tells you to sit down and wait.