What are the roots of sauna benefits? Let's start with this. Getting into great shape provides all kinds of physiological benefits, from stronger muscles to greater cardiac efficiency. A less obvious but equally critical boost: better heat tolerance. This allows us to perform better in the swelter (five sets at high noon on center court). But it also helps us better deal with internally generated heat—up to 75 percent of the energy from muscle contractions comes in the form of heat, not productive work.

Heat Tolerance & Sauna Benefits

One way, of course, to increase heat tolerance is to exercise vigorously in it, though this can be dangerous when temperature and humidity levels soar. Fortunately, researchers may have found a new way to acclimatize passively, if not entirely painlessly: post-workout sauna training.

Lance Armstrong got his edge from EPO, which increases blood volume. Turns out, you can boost yours naturally ... in the sauna.

Sauna benefits for endurance athletes? “The evidence that this can significantly enhance endurance is very strong,” says exercise physiologist Stacy T Sims, Ph.D., an adjunct researcher at Stanford University’s Prevention Research Center. “Our current interest stems from the old-school use of sauna exposure by cross-country skiers, pro cyclists, and other endurance athletes. Their mostly European coaches would have them sit in the sauna post-training to help with recovery and sweating capabilities.”

A Trigger for Natural EPO

Such traditional explanations of sauna benefits might play some role, but Sims and her colleagues suspect there’s a more potent reason that sauna heat fires up sports performance. As the sauna gradually warms up our core temperature, she explains, sensors in our brains trigger sweating to keep us from parboiling. Sweating in a sauna, of course, doesn’t do much to cool us. But it does have a secondary effect. Since the liquid in sweat comes mainly from blood plasma, the more we drip, the more dehydrated and difficult to pump our blood becomes. This decreases oxygen tension in the kidneys, triggering the release of a natural hormone called erythropoietin, or EPO, which, in turn, stimulates red blood cell production and increases blood volume.

Chances are you’ve heard of EPO before. Synthetic forms have long been used medicinally to treat serious health conditions like anemia. Lance Armstrong admitted to taking it, too, despite its ban by World Anti-Doping Agency for being an illegal blood doper.

But boosting your own body’s supply naturally is entirely kosher. In fact, most athletes do this, at least to some extent, during our workouts thanks to dehydration. Some sports, of course, are legendary for their dehydrating potential. Marathon runners, for instance, have been known to lose more than 1.5 gallons of sweat—and 10 percent of their body weight—during summer races. It’s not prolonged endurance exercise in a hot environment that causes it, either. Even swimmers sweat, even though it’s hard to see them do it. The water doesn’t even have to be particularly warm, either.

For a study in Science & Sports, for instance, competitive male swimmers agreed to race a 5K three different times in different pool temperatures. When the water was a stifling 90 ̊F, the swimmers lost up to 3.5 pints of sweat per hour; at a comfortable 80 ̊F, the rate was still nearly 2.5 pints; and even at a chilly 73 ̊F, they lost up to 1.6 pints per hour.

Why does losing water weight mid-event matter? “One of the primary factors in endurance muscle fatigue is this drop in blood volume,” Dr. Sims explains. “Sauna training helps counter this by increasing EPO and, through this, both plasma volume and red blood cell count. It can be super-beneficial for any endurance athlete. Think of it as another natural ergonomic aid in your arsenal, one that can provide a 2 to 3 percent boost in performance.”

To maximize the benefit, Sim’s has developed a protocol to use before any major event likely to challenge you to your limits. Make sure to check with your doctor first, especially if you take medications (including NSAIDs like ibuprofen or naproxen, which reduce blood flow through the kidneys) or suffer hypertension, kidney problems, or other serious health problems.

10 Tips To Maximize Sauna Benefits

Begin sauna training at least two weeks before your event.
Soon after each daily workout, enter the sauna set to 185 to 195 ̊F degrees.
Try not to drink anything before or during your time in the sauna—the point is to increase dehydration.
If you need a break, get out briefly, pour cold water on your neck and tongue, then return.
Stay seated and don’t exercise. Passive sauna bathing alone will increase your resting heart rate to 140 to 150 beats per minute or faster.
Many younger adults can gradually work up to 30 to 35 minutes exposure per session, but older folks may need to cut this time in half.
Never remain in the sauna if you start to feel sick. Do not become competitive with yourself or others.
After exiting the sauna, resist the urge to gulp water. Instead, sip fluids gradually over the next 3 to 4 hours.
Repeat the above every day for at least a week, even on rest days.
One week before your event, stop sauna training completely and let your system recover and rebound. This will maximize the increase in blood volume and set you up for enhanced performance on the big day.

Final note: You can maintain EPO’s benefits for up to six weeks by taking a long sauna once every ten days.

Legendary wrestler and wrestling coach Dan Gable gives his take on sauna benefits.

Jim Thornton

Jim Thornton is a National Magazine Award–winning freelance writer living in Pittsburgh.