Swimming and other water-based exercises are one of the most effective forms of physical activity for people with osteoarthritis. The combination of buoyancy, warmth, and gentle resistance makes a pool uniquely suited for joints that hurt under load. Clinical trials show aquatic exercise reduces pain by up to 50%, improves physical function, and builds the muscle strength that protects damaged cartilage.
Why Water Works for Arthritic Joints
The core advantage of exercising in water is simple: you weigh less. In chest-high water, your apparent body weight drops to roughly 32 to 35% of what it is on land. That translates directly to your joints. Researchers using instrumented hip and knee implants found that standing on one leg in chest-high water reduced hip joint forces by 58% and knee joint forces by 62% compared to the same position on dry ground. Every 10 centimeters of additional water depth reduced joint loading by another 29% of body weight.
That dramatic reduction in load lets you move through a range of motion that might be painful or impossible on land. At the same time, water provides resistance in every direction you move, so your muscles still get a workout. This matters because stronger muscles around the hip and knee absorb and distribute your body weight more effectively, increasing joint stability and improving how you walk. Water essentially lets you strengthen the muscles that protect your joints without punishing those joints in the process.
Warm water adds another layer of benefit. Pool temperatures between 83 and 88°F (28 to 31°C) are ideal for exercise, relaxing muscles and reducing the stiffness that makes the first few minutes of movement so uncomfortable. Therapeutic pools used in clinical trials typically sit around 89 to 90°F (32°C). If you’re soaking in a spa or hot tub rather than actively exercising, temperatures up to 104°F are generally safe, but limit those sessions to 10 to 15 minutes.
What the Pain and Function Numbers Show
A randomized controlled trial comparing aquatic exercise to land-based exercise in people with knee osteoarthritis produced striking results. After the program, participants in the water group saw a 50% reduction in pain scores, compared to 17% in the land-based group. Stiffness dropped by 53% in the water group versus 18% on land. Physical function improved by 48% in the water group, compared to just 11% for those exercising on land.
The gap held across nearly every measure. When researchers defined a meaningful response as at least a 20% drop in pain, 93% of the aquatic group hit that threshold. Only 33% of the land-based group did. Quality of life scores told the same story: physical health ratings improved by 5.4 points in the water group versus 2.3 on land, and mental health scores improved by 10.9 points versus 6.3.
These findings don’t mean land-based exercise is useless. Walking, cycling, and strength training all help osteoarthritis, and the European Alliance of Associations for Rheumatology (EULAR) notes in its 2023 guidelines that neither aquatic nor land-based exercise is clearly superior to the other across all studies. The choice should come down to what you have access to and what you’ll actually do consistently. But for people who find land exercise too painful, water provides a way in.
Swimming vs. Other Pool Exercises
Swimming laps is just one option. Many of the clinical trials showing benefits used structured aquatic exercise programs that included walking or jogging in waist- or chest-deep water, resistance exercises using the water itself or foam equipment, and stretching. One well-designed 18-week trial had participants doing 50-minute sessions of stretching and strengthening in chest-deep water at 32°C, three days per week, and found water-based exercise to be an effective alternative for managing knee osteoarthritis.
If you’re a confident swimmer, laps work well because they engage large muscle groups with minimal joint impact. Freestyle and backstroke are generally gentler on the knees and hips than breaststroke, which requires a wide kicking motion that can stress the inner knee. But you don’t need to swim at all to benefit. Walking back and forth across a pool, doing leg lifts while holding the wall, or simply moving your arms and legs through the water’s resistance all count. The Arthritis Foundation notes that combining strengthening, stretching, and cardiovascular activity in water reduces pain, restores flexibility, and improves heart and lung health.
How Often and How Long
Most studies showing clear benefits used programs of two to three sessions per week, with each session lasting 45 to 60 minutes. That tracks with general exercise recommendations for osteoarthritis. You don’t need to start there. If your joints are very stiff or you haven’t been active, beginning with 15 to 20 minutes of gentle movement in warm water and gradually increasing is a reasonable approach.
Consistency matters more than intensity. The improvements seen in clinical trials came from programs lasting 8 to 18 weeks, not from a handful of pool visits. Treating it like a regular part of your week, rather than an occasional dip, is what produces lasting changes in pain and function.
Getting Into the Pool With Limited Mobility
One practical barrier is actually getting into the water. If your knees or hips are severely affected, climbing a pool ladder can feel like the hardest part of the workout. Look for pools with sloped entries (zero-depth or beach-style entries), wide stairs with sturdy handrails, or pool lifts. Public pools in the United States are required under the Americans with Disabilities Act to provide at least one accessible means of entry, such as a pool lift or sloped ramp. Larger pools (those with more than 300 linear feet of wall) must have two accessible entry points.
Community recreation centers, YMCA locations, and physical therapy clinics with therapy pools are often the easiest places to find both warm water and accessible entry. Some physical therapy practices offer structured aquatic therapy programs led by a therapist, which can be a good starting point if you want guidance on what exercises to do and how to progress safely. Once you’re comfortable with a routine, transitioning to a regular pool on your own is straightforward.
What Water Exercise Cannot Do
Aquatic exercise relieves symptoms and builds strength, but it does not reverse cartilage damage. Osteoarthritis involves the gradual breakdown of the cartilage cushioning your joints, and no exercise program, in water or on land, rebuilds that cartilage once it’s significantly worn. What exercise does is slow the process, reduce pain, and improve how well you can move day to day. Researchers have begun studying whether aquatic resistance exercise changes the biochemical composition or thickness of knee cartilage, but that work is still in early stages with no conclusive results yet.
Water exercise also doesn’t build bone density the way weight-bearing activities like walking do. If osteoporosis is a concern alongside your arthritis, supplementing pool workouts with some land-based activity, even short walks, helps maintain bone strength. The two approaches complement each other well: the pool protects your joints while land-based movement protects your bones.