Can aerobic exercise still be done when the knee joint is degenerating? Among walking, cycling and swimming, which suits the person best? Many people in Hong Kong with knee osteoarthritis shrink back at the words aerobic exercise, worried that the more the joint moves the more it will be damaged. In fact, the real issue was never "whether it can be done". It is "which kind to choose and how much to do". The UK NICE NG226 (2022) guideline long ago listed general aerobic fitness explicitly as one of the core exercise treatments for all people with osteoarthritis. In other words, aerobic exercise is itself an important part of the treatment prescription.
Low-impact aerobic exercise brings a double benefit for people with knee osteoarthritis.It trains the heart and lungs and helps to control weight, which reduces the stress on the knee joint. There is also scientific evidence that exercise itself directly eases the pain of knee osteoarthritis and improves joint function. Research confirms that exercise on land relieves pain effectively (supported by high-quality evidence), and water exercise also brings a small but clinically meaningful improvement. Many older adults in Hong Kong with knee osteoarthritis also have the "three highs" (high blood pressure, high blood sugar and high cholesterol) and are overweight, and low-impact aerobic exercise looks after both heart health and the knee joint.
This article concentrates on one core question: what is the medical evidence for each of the three low-impact aerobic exercises of walking, stationary cycling and water exercise, how to choose between them, and how much exercise to do. (Topics such as the progression of quadriceps strength training and the safety comparison of squats and tai chi belong to other articles, and are only linked here without repeating them.)
Walking, cycling and water exercise compared
Low-impact aerobic exercise means reducing as far as possible the impact on the knee joint when the feet land. All three exercises below can do this, but their entry barriers and the people they suit differ. None is absolutely the "best", and the question is only "which is suitable".
The medical evidence for each and the people each suits are set out one by one below. One point has to be made first: most of the figures quoted below are benefits that are "small to moderate and mostly short term". Aerobic exercise certainly helps the condition, but it is not a miracle cure that changes everything at once, and the key remains to practise continuously and regularly.
Benefits of walking and controlling the amount
In Hong Kong, walking is the easiest low-impact aerobic exercise to put into practice. All that is needed is to go to the park downstairs or a flat road, with no equipment to buy and no entrance fee. In fact, the medical evidence for exercise on land relieving pain is quite solid. A Cochrane systematic review that pooled 44 clinical trials with over three thousand people (Fransen 2015) found that exercise relieves pain immediately (SMD −0.49, equal to a fall of about 12 points on a 0–100 scale) and improves physical function (SMD −0.52, about 10 points of improvement), and the pain-relieving effect rests on high-quality evidence.
However, walking is not a case of "the more the better". A dose-escalation study in people with severe knee osteoarthritis (Wallis 2015, 24 participants, with exercise raised from 10 minutes a week step by step to 95 minutes) found that about 70 minutes a week of supervised walking at moderate intensity was safe and feasible, but going beyond that time risks making the knee pain worse (the trial was stopped when adverse events occurred at 95 minutes). This has to be made clear: the 70 minutes above comes from a phase I feasibility study in severe cases and serves only as a reference marker for a "cautious starting point". It is not a general prescription for everyone. For how the whole exercise programme beyond walking should be spread across a week, how much of each to do, and how to increase the amount step by step, see the article on how to plan a weekly aerobic dose.
The point of walking is to start with a little and slowly increase. The UK NICE NG226 guideline says that some mild joint pain may appear when exercise is just starting, which is normal. It works if it is done continuously and regularly, and the benefit of keeping going over the long term is greater. If the joint stays red and swollen or the pain gets worse after exercise, the amount has to be adjusted. See the article on what to do when knee pain gets worse after exercise for how to deal with it.
Features and effects of cycling
If a person is afraid of the impact when the feet land, has poor balance, or would like to exercise safely at home (using a home exercise bike), a stationary bike is quite an ideal choice. Because the body weight is supported by the saddle when pedalling seated, the load on the knee joint is naturally lower. For medical evidence, a meta-analysis of 8 studies with 724 people in total (Luan 2021) showed that stationary cycling helps to reduce pain (WMD 12.86, 95% CI 6.90–18.81) and improves sport performance (WMD 8.06, 95% CI 0.92–15.20).
One point must be added objectively here: the same analysis also states that the improvement from cycling in daily function, daily activities and quality of life may not reach the threshold of being "clinically meaningful (MCID)". In other words, although a stationary bike is an ideal tool for relieving pain and training the heart and lungs, it is not a cure-all. It suits people who are afraid of impact on landing, have weaker balance or a limited range of knee movement, as part of low-impact aerobic exercise. Incidentally, a stationary bike is also a common rehabilitation device after total knee replacement, but the purpose of cycling after surgery is not to chase an amount of cardiorespiratory exercise. It is to bring the joint to a particular bending angle, and the related standards can be found in bending angle goals after knee replacement.
Features and effects of water exercise
When the knee hurts badly as soon as it moves, the person is heavy, or is very afraid of falling, even taking the first step may feel hard when exercising on land. The buoyancy of water takes most of the body weight off, letting the joint move under a low load, which is the greatest value of water exercise. The Cochrane systematic review (Bartels 2016) pooled the data of more than ten clinical trials and over a thousand participants and reached the following conclusions:
The exercise programmes in the studies above lasted 12 weeks on average, and no serious adverse events occurred during that time. The study authors described these benefits as "small, short-term but clinically meaningful", which is a fair way to put it, and patients should not expect an instant miracle. For the situations in which water exercise should especially be considered, the OARSI 2019 guideline gives a clear direction: structured exercise on land is the core treatment for all people with knee osteoarthritis, while water exercise is a "comorbidity-dependent" treatment option. This means that for people who also have other health problems (such as being overweight, a heavy heart and lung load or severe pain) that make it hard to exercise on land, water exercise is especially worth considering.
Water exercise has "small, short-term but clinically meaningful" benefits for relieving pain and improving function and quality of life, and no serious adverse events occurred in the studies.
In Hong Kong, water exercise is an extra option when conditions allow. Because of limits on swimming pool facilities, the weather and personal equipment, not everyone finds water exercise convenient. In the real environment, walking in the park downstairs or pedalling an exercise bike at home suits the way of life of people in Hong Kong better. If there is a pool nearby and the person's physical condition particularly suits it, water exercise is a very good choice.
How to choose the aerobic exercise that suits you
In the end there is only one key principle: there is no "best" aerobic exercise, only the one that "fits the person's ability and that the person is willing to keep up for a long time". The American ACR 2019 guideline has made it clear that among types of exercise such as walking and water exercise there is "no hierarchy", and that exercise supervised and guided by a professionaloften works better. So instead of agonising over "which exercise is most effective", it is better to ask "which one can I really do and keep doing for a long time".
How long does the benefit of a structured exercise programme last? A real-world registry study of nearly ten thousand patients (GLA:D, Skou & Roos 2017) showed that after taking part in a structured exercise programme with someone guiding it, patients' pain level (VAS) improved by 12.4 points at 3 months and the improvement was still 13.7 points at 12 months, and quality of life also kept rising from month 3 to month 12. This shows well that, as long as the person keeps going, the benefit of exercise can last up to a year, and it is also why "choosing an exercise that can be kept up" matters so much.
- 1Look at your own situationDo you have severe pain, are you overweight or afraid of falling? Are you afraid of impact on landing, or do you want to exercise at home? Or do you want zero cost and to fit exercise into daily life? It is worth matching yourself to the groups first.
- 2Choose one you can doWater exercise, cycling and walking have no "best" among them. What matters most is that you can do it and can keep it up in the long term.
- 3Start with a little and increase step by stepThe amount of exercise should start small, to give the joint and muscles time to adapt. Those who choose walking should especially watch the walking distance.
- 4Find someone to guide you and keep goingExercise with a person guiding it works better. The benefit of a systematic exercise programme can also last up to a year (GLA:D).
Related medical evidence and research limits
While encouraging exercise, the research limits below also have to be set out clearly. The overall conclusion points in a consistent direction (aerobic exercise really is worth doing), but patients should keep reasonable expectations of the size of the benefit.
- Listed as a core exercise treatment by NICE NG226, and a strong recommendation by ACR 2019
- High-quality evidence for pain relief on land, and small but clinically meaningful benefit in water
- Looks after the heart and blood vessels and body weight together, which kills two birds with one stone for older adults in Hong Kong with the three highs or overweight
- In a structured programme with guidance, the benefit can last up to a year (GLA:D)
- Missing the benefits for pain relief and function that the guidelines list as first-line and core
- Heart and lung fitness and body weight both slip, which indirectly puts more stress on the knee joint
- The less the person moves, the easier it is to fall into a cycle of pain and decline
Strength training and aerobic exercise need to go together. This article is mainly about choosing aerobic exercise. To learn how to train the quadriceps at the front of the thigh step by step (for example straight leg raises, small squats and sit-to-stand practice), see the article on the quadriceps as the natural brace for knee osteoarthritis. For general exercise prescription and fall-prevention balance practice, see physiotherapy and regular exercise and balance and fall-prevention training. For joint stability and neuromuscular control practice targeted at knee osteoarthritis, see the article on balance training for knee osteoarthritis.
Exercise advice for people with knee osteoarthritis
The principles below are a clinical practice consensus in physiotherapy, and help patients turn the medical evidence above into a habit of low-impact aerobic exercise that they can do and keep up over time.
- Have a physiotherapist first assess the level of pain, body weight, heart and lung function and mobility, and then suggest the type and amount of aerobic exercise to suit the individual. This is safer and more effective than everyone using the same method.
- Choose an exercise you can keep up in the long term: people with severe pain, who are overweight or afraid of falling can consider water exercise first. People worried about impact on landing or who want to exercise indoors can choose cycling. People who want to spend nothing and fit exercise into daily life can choose walking.
- Start the exercise with a little and progress step by step. When walking, especially control the distance, and in severe cases about 70 minutes a week can be used as a starting point, to give the knee joint time to adapt slowly.
- As far as possible, exercise under professional guidance and keep practising regularly. Research confirms that the effect of a systematic exercise programme can last up to a year.
- Do not avoid aerobic exercise completely for fear of hurting the knee. This not only means missing the pain relief and functional benefit that international guidelines list as a first-line treatment, but heart health and weight control will suffer too.
All of the principles above, however, share one precondition: the patient must be able to get to the place of exercise. With knee pain, going down stairs, walking on slopes and even avoiding passers-by in the street are layer upon layer of difficulty in themselves. Some patients cannot even manage to walk to the park downstairs, and of the three exercise options only the one that can be done at home is left. This is the very difficulty that home exercise therapydeals with: it moves the starting point of exercise back to the patient's home, removing the obstacle of first having to get past the hurdle of going out.
To return to the overview page of this topic, go to the exercise programme for knee osteoarthritis, or browse the knee osteoarthritis overview for the overall direction of treatment.