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Sports science, like the rest of the universe, doesn’t obey any rules of karmic balance. But on some deeply submerged level, most of us think it should. Do you realize how uncomfortable that ice bath was, or how expensive that platelet injection was? Of course it’s going to make me faster and stronger!

I suspect that’s part of the reason I’ve gotten so many inquiries about hot yoga over the past decade since I started writing this column. It’s so mind-bogglingly hot, and so drippingly sweaty, and such an overall intense experience, that it must be doing something awesome, my friends and correspondents insist.

So, to be totally honest, it’s almost a relief to finally report that yes, hot yoga is awesome. The news comes courtesy of a new study published in the Journal of Strength and Conditioning Research, from scientists at the University of British Columbia and Simon Fraser University. They reveal that the national women’s field hockey team experimented with hot yoga during their (ultimately unsuccessful) efforts to qualify for the 2016 Olympics Games in Rio – and gained measurable performance benefits.

The key ingredient of hot yoga, from a performance perspective, is its heat. It’s well established that repeated exposure to heat triggers a series of adaptations, such as an increase in the amount of blood plasma flowing through your veins, that enhance your ability to exercise in hot conditions. In the past few years, evidence has emerged that heat adaptation can also boost your endurance even in cool conditions, sparking a surge of interest in various forms of heat training.

The challenge for elite athletes, explains Andrew Perrotta, a recent graduate of the University of British Columbia’s experimental-medicine program and the former head physiologist for Field Hockey Canada, is figuring out how to add heat without disrupting the rest of your training. Running on a treadmill in a heat chamber will boost your heat tolerance, but likely leave you too drained to perform well in your next workout.

Hot yoga, Perrotta figured, would deliver a dose of heat training without exhausting the athletes. In addition, the format of hot-yoga classes enables a whole team to participate at the same time, which is far more practical than booking individual sessions in a heat chamber.

To test the idea, 10 national-team field-hockey players did a series of six hot-yoga classes, each consisting of 30 minutes of dynamic movements and 30 minutes of static stretching. They swallowed ingestible thermometer pills to track their core temperature, completed exercise testing before and after the six days of yoga, and then, two days later, headed to a national-team training camp.

Daily blood tests showed that plasma volume, instead of increasing as expected, actually decreased progressively during the six days of yoga. In hindsight, Perrotta suspects this may be a result of mild dehydration, since the players were instructed not to drink during the hot-yoga session. But once the players resumed normal workouts at their training camp, their plasma volume immediately shot up to 5 per cent above its baseline level – a significant boost that was accompanied by improvements in running speed during their exercise tests.

The results suggest that hot yoga is indeed a useful tool for heat adaptation, says Chris Minson, a physiologist at the University of Oregon who researches heat training and was not involved in the study.

One caveat, Minson notes, is that the observed increases in core temperature – about half a degree Celsius – are smaller than those seen in most heat studies. The yoga in the study was performed in a room at 30 C and roughly 50-per-cent humidity; since many hot-yoga classes are performed in 40-degree heat, there’s potential for an even stronger stimulus.

That suggests there really is something to the karmic idea that the more you sweat, the more you benefit – up to a point, at least. But Perrotta adds another wrinkle: “One aspect that I didn’t investigate was the psychological effect,” he says. “The meditative component may be important, especially when entering a competition period.”

In other words, taking up hot yoga just to chase plasma volume risks missing the larger point of the practice. Still, if you’re doing it anyway, it’s nice to know that your sweat will be rewarded.

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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