Heat Acclimatisation for Summer Racing

Racing in the heat is a serious challenge — and one that catches many UK-based triathletes completely off guard. After months of cool, grey training, arriving at a summer destination race to face 25-35°C temperatures can shatter a perfectly prepared race. The good news: your body can adapt, and targeted heat acclimatisation strategies can protect your performance.

What Happens in the Heat

When core temperature rises, your body redirects blood flow to the skin for cooling — reducing the blood available to working muscles. Heart rate climbs at the same effort level as in cooler conditions, hydration demands spike, and perceived exertion increases. Without preparation, this can cause a 5-10% drop in performance in even moderately warm conditions.

How Long Does Acclimatisation Take?

Meaningful heat adaptation begins within 3-5 days and is largely complete after 10-14 days of heat exposure. Key physiological changes include increased plasma volume, earlier and more effective sweating, reduced heart rate at the same effort level, and improved muscle glycogen use efficiency.

Practical Heat Training Strategies

Train in the heat. If your race is in a hot location, train outdoors at the warmest part of the day for 30-60 minutes daily in the 10-14 days before. Build from 20 minutes and add 5 minutes per session.

Hot bath immersion. If you cannot train in the heat, submerge in a hot bath (38-40°C) for 20-30 minutes after your normal training session for 7-10 days. Research shows this can improve 5km running performance in 30°C heat by nearly 5% when done consistently.

Sauna sessions. A 20-minute post-workout sauna session (3-4 times per week) significantly increases plasma volume and improves heat tolerance over 2-3 weeks.

Heat pre-cooling. Before race start, use ice vests, cold towels, or cold drinks to lower core temperature. Research shows this can delay the onset of heat-related performance decline by 10-15 minutes.

Race Day in the Heat

• Reduce your target pace or power by 5-10% and go by RPE rather than fixed pace targets
• Drink to thirst and use electrolytes — sweat losses can reach 1.5-2 litres per hour in extreme heat
• Pour water over your head and neck at every aid station during the run
• Wear light-coloured, loose-fitting, moisture-wicking kit — dark colours absorb significantly more heat
• Start the run conservatively: the run in hot conditions is where most athletes blow up

Acclimatising in the UK

If your hot-weather race is in June-September, the UK summer can be warmer than expected. Plan outdoor brick sessions during the warmest afternoon windows and consider hot bath protocols starting 2 weeks out from your A-race. Heat acclimatisation is a legal, safe, and highly effective performance booster — start early and arrive prepared.