Heat training for marathoners
More amateur marathoners are using heat training — hot baths and sauna‑style adaptation — as a tool to prepare for spring marathons like London and Boston, a trend coaches say improves heat tolerance and endurance (independent.co.uk). Paired with smarter fueling and hydration strategies designed to prevent hitting the wall over 26.2 miles, the practical takeaway is clear: adapt to likely race conditions and dial in fueling to avoid late‑race collapses (independent.co.uk).
Heat training for marathoners A hot bath used to be recovery. Now, for a growing number of amateur marathoners, it is part of training. Ahead of the 2026 Boston Marathon on April 20 and the 2026 London Marathon on April 26, coaches and runners are treating heat exposure as another workout variable, alongside mileage, long runs, and pace sessions. The idea is simple: if race day turns warm, the body that has practiced handling heat is less likely to unravel late in the race. That shift reflects a basic fact about the marathon. The race is 26.2 miles long, and the body is producing heat the entire time. Even on a day that feels mild to spectators, a runner moving hard for three, four, or five hours is constantly balancing heat production, sweat loss, and pace. When that balance slips, performance usually goes with it. Heat training is meant to teach the body to manage that load better. Sports bodies including World Athletics describe heat acclimation as a way to reduce heat strain and improve performance in hot conditions, usually through repeated exposure over roughly two weeks. The best-known version is exercising in the heat, but passive options like sauna bathing and hot water immersion are now widely discussed because they are easier for ordinary runners to fit around work and family life. The attraction is convenience. Most amateur runners cannot spend two weeks training in Florida, Arizona, or a climate chamber. Many can, however, finish an easy run and sit in a sauna for 30 to 40 minutes, or get into a hot bath while core temperature is still elevated from exercise. World Athletics guidance specifically lists hot water immersion and sauna bathing as passive heat-acclimation options before or after training. The physiology is not magic. Repeated heat exposure can expand plasma volume, which is the liquid part of blood, and can improve sweating responses and cardiovascular stability. In plain terms, the body gets better at moving heat away from working muscles and out through the skin, while the heart does not have to strain as much at a given pace. That is why hot baths have moved from fringe hack to plausible training tool. A recent systematic review on post-exercise passive heat acclimation found evidence that sauna bathing or hot water immersion after normal training can improve exercise performance in the heat, although the researchers also noted that the full effect size and best protocol are still not settled. In other words, the science is promising, but not every runner should expect a miracle from sitting in hot water. There is also a limit to what heat training can do. World Athletics says passive heat methods are alternatives when training in hot conditions is not possible, but overall benefits are likely smaller than actually exercising in the heat. That matters because some runners hear “sauna” and assume they have replaced specific race preparation; they have not. The second half of the story is fuel. Marathoners do not only slow down because they get hot. They also slow down because they run low on available carbohydrate, which is the body’s quickest race fuel. Sports nutrition guidance for endurance athletes has steadily pushed runners toward more deliberate carbohydrate plans before and during long events, rather than relying on one gel when things start going wrong. That is the logic behind the phrase runners use for late-race collapse: “hitting the wall.” Muscle glycogen, the stored form of carbohydrate, is finite. If pacing is too ambitious, intake is too low, or both happen together, the final 10 kilometers can feel less like fatigue and more like the floor dropping out. Hydration is the same kind of problem: simple in theory, individual in practice. The American College of Sports Medicine says the goal is to begin exercise well hydrated and avoid excessive dehydration, while newer practical guidance warns against both underdrinking and overdrinking. For marathoners, that means copying another runner’s bottle plan can be as risky as copying their interval session. (acsm.org/
