When a doctor says the word “exercise” people with knee pain experience a certain kind of dread. It seems contradictory. When the knee hurts, the natural reaction is to shield it by remaining motionless and waiting for the pain to go away on its own. It turns out that this instinct quietly crumbles in swimming pools.
The question of which exercise is most effective for treating knee osteoarthritis has been the focus of years of research. After combining data from 217 randomized trials with almost 15,700 participants, a team published the solution in “The BMJ” in October 2025. For pain relief and function restoration, walking, cycling, and swimming outperformed strength training, yoga, and balance exercises. In particular, swimming continued to appear in the company of the other two as a regular activity rather than a curiosity.
| Category | Detail |
|---|---|
| Topic | Swimming for knee pain relief and joint health |
| Primary joints affected | Knees, hips, and lower spine |
| Recommended frequency | 2–3 sessions weekly, roughly 30–45 minutes per session |
| Evidence base | 217 randomized controlled trials, 15,684 participants (BMJ, 2025) |
| Endorsing bodies | Osteoarthritis Research Society International, American College of Rheumatology, EULAR |
| Calories burned (moderate pace, 1 hour) | Approximately 400 or more |
| Key limitation | Non-weight-bearing, so it does not build bone density |
| Authoritative reference | Harvard Health, “Walking, cycling, and swimming are best exercises for knee osteoarthritis” |
Given that the mechanism is not mysterious, it is worthwhile to consider why that is the case. A swimmer is held up by the water. Once a person is submerged to chest depth, about 90% of their body weight is offloaded, so the knee is no longer receiving the same hammering impact as it would on a sidewalk or a treadmill. That difference is noticeable for a joint that is already inflamed or has lost some of its cartilage cushioning. It’s the difference between grimacing during a stroll and hardly realizing that forty-five minutes have gone by.
Beneath the surface, there’s also something that seems almost counterintuitive. Because water resists movement more than air, the surrounding muscles the quadriceps, hamstrings, and stabilizers around the hip are constantly working against this resistance even as the knee is spared the pounding. Over the next few weeks, strengthening those muscles usually relieves pressure on the joint.
According to a 2016 University of Texas study, older adults with osteoarthritis who swam three times a week for three months experienced double-digit increases in knee strength along with significant decreases in pain and stiffness. In the same study, cycling yielded almost identical results, which suggests that the body doesn’t really care which low-impact exercise provides the resistance as long as it’s consistent.
All of this does not imply that every stroke is made equal, a fact that is overlooked in the majority of the upbeat advice columns regarding pool jumping. With its long overhead reach, front crawl puts a lot of strain on the shoulder. Anyone who has swum competitively has probably experienced rotator cuff pain following a demanding week of laps.
That’s largely irrelevant for someone dealing with knee pain in particular, but it serves as a reminder that swimming isn’t always a gentle activity just because it takes place in water. Because of its whipping kick, breaststroke can actually make some knee conditions worse rather than better. Almost as important as deciding to swim at all is selecting the appropriate stroke.
When swimming is stripped of impact, people are often surprised by how much it resembles walking mechanically. In clinical literature, water walking just swimming through a pool at waist or chest depth is frequently mentioned as a valid alternative to laps, especially for individuals whose knees are too sore for extended swimming sessions. It’s slower, less glamorous, and somehow still effective: the resistance of the water alone can work the surrounding muscles and raise heart rate without ever putting any strain on the joint.
There is a more subdued benefit that patients frequently describe first but researchers mention almost as an afterthought. Mood is altered by pain. Particularly, anxiety and low-grade depression the kind that wears people down but isn’t always diagnosed have been linked to chronic knee pain. Almost any type of exercise tends to counter that, and swimming appears to do it effectively possibly because it’s difficult to ruminate while concentrating on breathing rhythm and stroke count.
To say that swimming is a perfect solution would be deceptive. People who swim as their only form of exercise are probably losing out on the bone-strengthening benefits that walking or light resistance training would otherwise offer because swimming has no effect on bone density because the skeleton isn’t bearing weight against gravity. Swimming is typically recommended by doctors as an entry point, a way to get a stiff, guarded knee moving again without aggravating it further, rather than as a replacement for all other forms of movement.
The feeling of relief at just being able to move without recoiling is more difficult to measure but appears in almost every discussion with those who have persevered. No one’s joint behaves exactly like the average in a clinical trial, so whether that effect lasts depends on consistency, technique, and the specific knee in question. The general trend, which has been repeated over decades of smaller studies and is now supported by one of the biggest reviews ever done on the topic, indicates that the pool is almost always a good place to start if you have a sore knee.
i) https://www.arthritis.org/health-wellness/healthy-living/physical-activity/other-activities/hit-the-pool
ii) https://flarin.co.uk/swimming-for-joint-pain/
iii) https://oldmrhc.org/blog/news/not-just-for-having-fun-consider-swimming-as-exercise/
iv) https://www.orthobethesda.com/blog/water-exercises-for-alleviating-arthritis/
v) https://drjnegus.com/blog/walking-vs-swimming-for-knees/