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Forget the postworkout ice bath – study suggests hot water, instead

British heptathlete Jessica Ennis-Hill has an ice bath to recover from competing. A new study is suggesting swapping the tradition ice bath for a soak in a hot tub.

Ian Walton/Getty Images

The epitome of the hard-core, no-pain-no-gain approach to training is the postworkout ice bath. After pushing your muscles to their limits, you soak them in teeth-chatteringly cold water to speed their recovery before the next gruelling workout.

But there may be a gentler, more soothing path to greatness.

A new study in the Scandinavian Journal of Medicine & Science in Sports suggests that swapping the ice tub for a relaxing soak in a hot bath can trigger performance-boosting adaptations that mimic how the body adjusts to hot weather. That is particularly valuable for those training through cold conditions – a Canadian winter, say – for a springtime race where the weather can be unexpectedly hot.

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Better yet, hot baths actually feel good, points out Neil Walsh, director of the Extremes Research Group at the Bangor University in Wales and the senior author of the new study.

"A hot soak is comfortable for aching limbs," he says, "and there are other supposed health benefits – think Roman spas."

Walsh's interest in the topic dates back to his days as a competitive road cyclist. "I'd always taken a hot bath after a long training ride, and it didn't make sense to me as a physiologist why a cold bath would be helpful."

The idea that hot baths, beyond being pleasant, might actually boost performance stems from recent research into heat adaptation. After one to two weeks of exercising in hot conditions, your core temperature will drop, your sweat rate will increase and you will produce a greater volume of blood plasma, all of which will enhance your ability to perform in the heat.

A controversial 2010 study from researchers at the University of Oregon suggested that the same process of heat adaptation could also enhance endurance in cool conditions. This idea remains hotly contested (it was the topic of a debate in the Journal of Physiology last month), but the study spurred interest in more convenient ways of triggering heat adaptation.

For example, an Australian study last year found that four days of 30-minute postrun saunas at 87 C produced a large increase in plasma volume.

Still, not everyone has easy access to a heat-controlled treadmill or a sauna, so Walsh and his colleagues wondered whether a simple hot bath could provide some of the same benefits. They recruited 17 volunteers to run for 40 minutes on a treadmill for six consecutive days, followed each time by a 40-minute bath submerged to the neck. Ten of the volunteers were assigned to hot baths at 40 C, while the other seven took "thermoneutral" baths at 34 C.

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By the end of the study, the hot-bath group had a lower resting rectal temperature by an average of 0.27 C, their temperature stayed lower during exercise and they began sweating sooner. Their performance in a five-kilometre treadmill trial improved by 5 per cent in hot conditions (33 C), though it didn't change in cool conditions (18 C).

These are compelling results – but it's worth nothing that the baths were pretty intense. On the first day, Walsh says, only four of the 10 hot-bath volunteers were able to complete 40 minutes, though nine of the 10 were able to complete it by the fifth day of adaptation. He and his colleagues hope to test less-onerous protocols in future studies: "As little as 20 minutes in the hot bath may be necessary to provide heat acclimation," he says, but "this needs confirmation."

So, will hot baths replace cold baths as the default postworkout soak? That depends on who you are, physiologist Trent Stellingwerff points out. Olympic endurance athletes such as those he works with at the Canadian Sport Institute Pacific in Victoria already have extremely high blood-plasma volumes, so hot baths may not provide enough of a stimulus to make any difference. Non-elite athletes, in contrast, might see a bigger benefit.

For now, there are few firm conclusions to be drawn. But if you are training through the winter for an event with potentially warm weather, a few hot baths seem like a low-risk insurance policy.

"I definitely felt the heat when I ran the Ottawa Marathon [in late May] in 2009," Guelph-based marathoner Reid Coolsaet recalls. "It wasn't even that hot, but I wasn't used to it at all."

Coolsaet plans to use a steam sauna to help him prepare for the expected heat of the Olympics in Brazil this year, though the late-summer timing of the Games means that he will not need much help getting used to muggy conditions. "Luckily," he says drily, "the weather in Guelph in July and August is comparable to that in Rio."

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If you do decide to try hot baths this winter, bear in mind that heat puts additional stress on the body. For starters, stick to 10 minutes at no more than 40 C (a standard upper limit for hot tubs), and get out immediately if you feel dizzy or nauseous.

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About the Author
Jockology columnist

Alex Hutchinson writes about the science of fitness and exercise. A former national-team distance runner and postdoctoral physicist, he is the author of Which Comes First, Cardio or Weights? Fitness Myths, Training Truths, and Other Surprising Discoveries from the Science of Exercise. He is also a senior editor at Canadian Running magazine and a contributing editor at Popular Mechanics. More

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