How to Manage a Heat Wave: A Physio's Guide to Staying Safe in Extreme Heat

What counts as a heat wave, and why it matters for recovery

The UK Health Security Agency (UKHSA) issues heat-health alerts once temperatures are expected to stay high enough, for long enough, to affect health — not just comfort. For most people that's a few uncomfortable days. For anyone recovering from surgery, managing a joint or muscle injury, or living with a long-term condition, it's a real physiological load on top of whatever they're already dealing with.

Heat widens blood vessels and increases fluid loss through sweat. That combination can worsen swelling in a recently operated joint, drop blood pressure enough to cause dizziness during exercises, and make fatigue and breathlessness appear at a much lower effort level than normal.

Who needs to be most careful

• Anyone within the first 6–12 weeks of joint replacement or surgery: heat encourages fluid to pool in the operated limb, on top of the swelling surgery already causes — see my knee replacement recovery guide for the swelling-management basics that matter even more in hot weather.
• Older adults: the body's ability to sense and respond to rising temperature declines with age, so heat stress can build before it's felt.
• People on certain medications: diuretics, some blood pressure medications, and some antidepressants all affect the body's ability to regulate temperature or fluid balance. If you're unsure about yours, ask your GP or pharmacist rather than guessing.
• Anyone with a long-term condition — heart disease, respiratory illness, diabetes — where heat adds a second stressor to a system already working harder than most.
• Babies, young children and pregnant women, whose temperature regulation is also less efficient.

This mirrors the risk groups in GOV.UK guidance for healthcare professionals on supporting vulnerable people in hot weather, which also recommends rescheduling physiotherapy to cooler times of day — the same advice I give my own patients.

Adjusting exercise and rehab, not skipping it

Reschedule, don't cancel

My default advice during a heat alert is the same one hospitals use for physiotherapy scheduling: move sessions to the coolest part of the day, usually early morning or later evening, and avoid the 11am–3pm window entirely. The exercises themselves don't need to change — the clock does.

Scale the effort, keep the frequency

• Drop intensity or reps by roughly a third on genuinely hot days rather than skipping the session — consistency matters more than any single day's volume.
• Move strength and balance work indoors to the coolest room available; save any outdoor walking for the cooler hours.
• Rest between sets a little longer than usual, and treat unusual dizziness or a racing heartbeat as a stop signal, not something to work through.

Watch for extra swelling

If you're managing a knee, ankle or post-surgical swelling normally, expect it to look slightly worse in a heat wave. Elevate the limb more often than usual, keep compression garments on if you've been prescribed them, and don't mistake heat-related swelling for a setback in your actual recovery — it usually settles within a day or two of the temperature dropping.

Cooling strategies that actually work

• Aim for a cool room under 26°C where possible — close curtains on the sun-facing side during the day and open windows once it's cooler outside than in.
• Cool showers, baths or a damp cloth on the neck and wrists bring body temperature down faster than fans alone once the room is already hot.
• Light, loose, breathable clothing and minimising direct sun exposure between 11am and 3pm.
• Cold, high-water-content food — fruit, salads, cold soups — contributes to hydration alongside drinking water regularly rather than only when thirsty.

For the fuller everyday toolkit, including where on the body to apply cold, shifting meal and training times, and reading hydration cues, see my practical guide to cooling your body down in hot weather.

Common misconceptions I see in my patients

• "I should push through my exercises to avoid falling behind." Rehab is cumulative over weeks, not decided by one session. Scaling back on a genuinely hot day protects the weeks either side of it.
• "More swelling means something's gone wrong." In a heat wave, mild extra swelling in a healing joint is usually the heat, not a complication — but a hot, red, rapidly swelling joint is always worth a same-day check regardless of the weather.
• "Fans are enough on their own." Once room air is above about 35°C, a fan mostly recirculates hot air. Combining a cooler room with cool showers and hydration works far better than a fan alone.

FAQ: managing a heat wave

Is it safe to exercise during a heat wave?

Usually yes, adjusted for timing and intensity — early morning or evening, indoors where possible, with reduced effort. Stop and cool down if you notice dizziness, nausea, a racing heart, or confusion, and treat those as heat exhaustion warning signs rather than something to push through.

Does hot weather make swelling after surgery worse?

It can, temporarily. Heat encourages fluid to pool in the limb on top of normal post-surgical swelling. Elevation, staying on top of any prescribed compression, and cooling strategies usually settle it within a day or two once temperatures drop.

Who is most at risk during a heat wave?

Older adults, babies and young children, pregnant women, anyone recovering from recent surgery, and people with long-term conditions such as heart disease, respiratory illness or diabetes.