As The Independent reports, sauna-bathing has boomed in the UK in recent months, particularly among Gen Z and millennials, keen to swap nights at the pub for a healthier way to unwind.
Many of these same quarter-life crisis runners might find themselves planning in a sauna in the lead-up to their marathon — detoxing the body, warming up the muscles, and easing those pre-race nerves. Sounds like a great idea, right? Wrong. And Brian Clarke, expert and founder of UK Saunas, explains why.
“For marathon prep, it’s the wrong tool at the wrong time. I wouldn’t recommend using the sauna 3 days prior to the race.” Brian says.
Why not? Here’s why sauna use is risky before a big race
Saunas can feel relaxing, even invigorating, and that’s part of the problem. They mask how much stress they place on your body. Brian breaks down the hidden risks:
1.Dehydration
“You’re not just sweating out water; you’re losing salts, electrolytes, and minerals your body needs to function over 26 miles,” Brian explains. “I've had runners tell me they cramped early in the race and didn’t connect it back to a sauna session the day before. But it’s a classic scenario.”
Even a short sauna session of 10-15 minutes can lead to significant fluid loss. That may not matter on a rest day, but before a marathon, it can tip your body into a deficit before you’ve even started.
2.You burn through fuel you should be saving
“Most people don’t realise you actually burn a fair few calories sitting in a sauna. All your hard work carb-loading in the lead up to the race will go to waste!”
Ten minutes in a 70-80°C sauna can burn approximately 70–100 calories, depending on body mass and metabolism. That’s fuel that would be better preserved for race day performance.
3.Additional physical stress
“Sauna bathing is a type of hormetic stress, which means it's good stress, when in the right context. But stacking that stress on top of race anxiety, travel, and disrupted sleep isn’t a smart decision.”
Increased heart rate, raised core body temperature, and elevated cortisol are all common effects of sauna use; this is the opposite of what you want when tapering and conserving energy.
4.You want muscle tension, not relaxation
“Before a marathon, you want your muscles to be primed in a slightly tight, springy, and responsive state. For efficiency and endurance in the race, you want to keep tension in your muscles and ligaments, but too much heat can overly relax tissues.”
When to use the sauna instead?
However, Brian is quick to point out that sauna therapy is great for recovery after the marathon: “The best time to use a sauna is after the race. That’s when your body can really benefit from it.”
How post-race sauna use can support recovery:
- "Heat encourages your body to produce heat shock proteins, which help repair muscle fibres and calm inflammation.
- After a marathon or any long effort, cortisol levels spike. Sauna sessions help bring those stress hormones back down by triggering the release of growth hormone and giving your endocrine system a nudge. That’s a big help for tissue recovery post-race.
- Your immune system also takes a hit after a marathon. Immune cells shift around, and cytokine levels can get out of balance. Time in the sauna helps boost white blood cell production, which can make it easier to fight off illness during recovery.
- Sitting in the heat also gives you a chance to mentally reset. The experience provides a meditative environment to relax and unwind after what may have been a gruelling training period and race day."