Around one in five UK adults has knee osteoarthritis, and the figure climbs sharply after 50. So when a GP, a physio or Versus Arthritis suggests swimming, they’re pointing at one of the most joint-friendly exercises available. Water-based exercise is a low-impact way to improve fitness, mobility and joint range of motion – that bit isn’t controversial. The detail is what matters: which stroke actually helps, which can flare a sore knee, what NHS hydrotherapy involves and how to access it, how often to swim without overdoing it, and the simple pain test that tells you when to ease back.
Why water works for arthritic joints
The physics make water unusually kind to sore joints. Buoyancy is the main reason. At waist depth, water supports about half your body weight. At neck depth, that effective load drops by around 90%. For knees and hips taking the brunt of osteoarthritis, that is a meaningful difference – you’re moving against gravity that’s been turned down.
Warmth matters too. A standard UK leisure pool sits around 28-30 degrees C – warm enough to relax muscles and improve blood flow without being uncomfortable. Dedicated hydrotherapy pools run warmer, typically 30-34 degrees C, for a deeper therapeutic effect.
Two other features add to the picture. Hydrostatic pressure – the gentle, even squeeze of water around the body – helps reduce joint swelling. And the resistance is multi-directional, so every push and pull gives you a light strengthening workout without any heavy lifting.
Versus Arthritis recommends water-based exercise across the conditions most likely to send you looking for help over 50: osteoarthritis of the knee or hip, rheumatoid arthritis between flares, chronic lower-back stiffness, and rehab after knee or hip replacement.
The strokes – what to favour and what to be careful with
Stroke choice matters more than most people expect. The wrong one for your joints will set back two weeks of good work in a single session.
Backstroke is the workhorse for arthritis. Spine in a neutral, supported position. No neck rotation. No impact at all. Your hips and knees move through a gentle, controlled range with each kick. If you’re going to pick one stroke as the default for sore knees and hips, this is it.
Front crawl (freestyle) is also kind to the legs – the gentle flutter kick is well tolerated. The catch is breathing. Repeated head turns can flare cervical spine arthritis if it’s already a problem area. Bilateral breathing – alternating sides every three strokes – distributes the rotation more evenly and helps a lot of people.
Breaststroke gets a mixed write-up. It’s good for upper-body strength and hip range of motion, but the wide whip kick is a known trigger for medial knee pain – the inside-of-the-knee ache that’s so common in knee OA. If breaststroke gives you that ache, the fix is simple: shrink the kick to a small flutter, or swap to backstroke for the rest of the session.
Butterfly is the one to leave alone unless a physio has explicitly cleared you for it. The dolphin-kick generates high impact through the lower back and shoulders.
Water aerobics, aquafit and over-50s sessions
If lap-swimming feels like a lot – or you don’t fancy deep water – aquafit is the better entry point. Most UK leisure centres run sessions branded “aqua-active”, “aquafit” or “over-50s aqua”, and many councils target them specifically at people with joint problems.
A typical 30-45 minute class works through a warm-up, mobility drills, light cardio (water marching, knee lifts, gentle jumping), strength work with foam dumbbells or resistance bands, and a cool-down. The water carries your weight; the kit adds manageable resistance. You get guided structure without having to count lengths.
These sessions also tend to be quieter and warmer than the main public swim. Worth phoning the centre to ask about water temperature – some run a “warm-water” or “therapy” slot a few times a week.
NHS hydrotherapy and aquatic physiotherapy
Hydrotherapy (also called aquatic physiotherapy) is a more targeted intervention than a general swim. It runs in a heated pool at 30-34 degrees C, supervised one-to-one or in a small group by a physiotherapist, and you’re guided through specific exercises tailored to your joints. A typical NHS course is 6-8 weekly sessions of around 30 minutes each.
It is available on the NHS, but it is not a routine first step. Access usually goes through a referral – GP, physiotherapist, rheumatologist or orthopaedic team. Most large NHS hospitals have access to a hydrotherapy pool, but it might not be at your nearest hospital, so some travel may be involved.
In some parts of the UK you can self-refer to NHS musculoskeletal (MSK) physiotherapy services. Worth checking with your GP practice or your local MSK service to find out the route in your area.
Versus Arthritis describes aquatic therapy as “particularly useful” for severe joint pain, post-surgical rehab, and people who find land-based exercise too painful. If land exercise is genuinely a barrier, ask about it.
How often, how long, and the 24-hour pain rule
The UK Chief Medical Officers recommend 150 minutes a week of moderate-intensity activity, plus muscle-strengthening on at least two days. For someone with sore arthritic joints, that target can sound like a lot. Realistic starting point: 2-3 sessions of 20-30 minutes a week. Build up gradually from there.
Versus Arthritis is clear that shorter, more frequent sessions beat one long, punishing weekly swim. Joint resilience is built by the regular dose, not the heroic effort.
The single most useful test of whether you’ve done too much is the 24-hour pain rule. A brief increase in stiffness or soreness for up to 24 hours after exercise is normal – your tissues are adapting. Pain that lasts more than 24 hours, or is sharper than your usual baseline, means you overdid it. Cut the duration or intensity of the next session by maybe a third, and rebuild.
Picking your pool and getting in cheaply
Standard UK leisure-centre pools run at 28-30 degrees C. For warmer water, look for venues that schedule “warm-water”, “therapy” or “over-50s” slots a few times a week, often in the 31-32 degrees C range. Hydrotherapy pools sit warmer at 33-35 degrees C, but those are on referral, not drop-in.
Cost is genuinely a barrier for some people. Two routes to know about. Many councils sell discounted leisure passes for over-60s, low income or disability. And many GP surgeries can refer into a local “Active Wellbeing” or “GP Referral” pathway that gives you 12 weeks of discounted or free leisure-centre access. Worth asking.
For confidence, skip the busiest early-morning lap-swim slots. “Adult swim”, “social swim” or over-50s sessions are calmer and friendlier. Well-fitting supportive swimwear helps; some people use neoprene swim shorts or aquatic knee supports for warmth and a little extra confidence.
⚠️ Stay-on-dry-land moments
Water exercise is overall very safe, but a few situations are non-negotiable stay-on-dry-land moments:
- An open wound or recent surgical incision (infection risk).
- An active gout flare.
- A recent steroid joint injection – typically wait 24-48 hours.
- Acute heart or breathing problems, uncontrolled high blood pressure, or a recent stroke.
- Severe vertigo.
- A skin or fungal nail infection (athlete’s foot, fungal toenails) – cover or treat first.
- A recent fall that’s left you with new joint pain – get the joint checked before loading it in the pool.
If any of those apply, a quick call to your GP or NHS 111 first is the right move.
