July 29, 2011

Are supporters of excess heat & sweat in yoga class just full of hot air? ~ Dan Pitko


Many yogis love heat and sweat. Others do not.

The claim: “sweat” is good for you because it “purifies” the body of “toxins.” Some also say that extra heat “opens” the body more, allowing a practitioner to “go deeper” in a posture and their practice.

Is there any merit to these claims of detoxification? Or are some studios and practitioners merely teaching their own body’s preferences, to the detriment of others? In at least one well known Los Angeles studio, tempers have flared with the temperature, resulting in verbal outbursts and window-slamming.

As the yoga population ages, it’s imperative to properly understand how the body cools itself, so that studios and practitioners alike do not inadvertently cause harm—and perhaps death—in the pursuit of “going deeper,” “detoxifying,” “healing,” and “love.”

While the prospect of a yogi passing away during class sounds unlikely, each year many people die during exercise, including high school and college athletes. Causes of death vary, but often heat stroke causes death or triggers another event, like cardiac arrest, especially when teams return to practice fields in the fall with 90 to 100 degree heat. In the recent heat wave in the United States, as of this writing, over 33 people have died, including an 18-year-old, and most were not exercising.

In the “alternative healing” arena, deaths have already occurred: James Arthur Ray, a spiritual teacher featured on Oprah and elsewhere, was recently convicted of manslaughter for causing the heat-induced deaths of three aspirants in an Arizona sweat lodge. Could such an incident happen in a yoga room?

Body Temperature

Body temperature is automatically regulated through a process called thermoregulation. A person’s ideal body temperature is based on many factors, including genetics, body type, diet, athletic background, and metabolism.

Body temperature is measured by a person’s core body temperature, which is the temperature inside of the body, as opposed to orally or in the ears or anus. Some general findings:

—Body temperature falls in a general range between 96°F and 99°F. 98.6°F is only an average.
—Women have higher temperatures than men, on average, but women have more day-to-day variability in their normal temperature due to hormonal changes in their menstrual cycle.
—Age is a factor. Younger people have higher body temperatures than older people. Younger people can regulate their temperature better than older people.
—Body temperature is lower in the morning than later in the day.
—Faster metabolic rate (the rate of chemical processes in the body) translates into a higher body temperature.
—Body mass: In general, people with more fat and muscle mass heat up faster and produce more excess heat during exercise. The extra mass acts as insulation, and generates more byproduct heat in a chemical reaction due to exercise. It also reduces their body’s surface-to-mass ratio, meaning that a smaller skin surface has to cool a larger body, as I write about later. At least one study also suggests that the higher the body mass, the lower the body temperature.

Keeping it Cool—Humidity is Key

When heated, the body increases its air and blood flow to transport heat outside the body: the breath quickens and the skin can turn pink. This helps transport heat outside the body.

If heat continues to build, the body then produces sweat. But sweat itself does not cool the body—the body turns the sweat into water vapor to transport heat outside the body in a process called evaporative cooling, or evaporative sweat.

This means that humidity is the main factor in cooling the body. Why? In high ambient humidity, the air cannot absorb water vapor from the body’s evaporative sweat process. An example is walking into a sauna—the body quickly heats up because evaporative cooling is not effective, and sweat pools on the skin, causing the body to heat faster.

Heat Index

The heat index was created to gauge what air temperature and relative humidity “feel like” to the human body. As described above, the body has a harder time cooling itself when humidity levels increase because evaporative sweat is less efficient. A heat index of 105, for example, means that the environment “feels like” 105 degrees.

The National Oceanic Atmospheric Administration (NOAA) developed a Heat Index Chart to provide guidance about exercising in the heat. “Caution” should be used when exercising in 80°F Heat Index and above; “extreme caution” when 91°F and above; it is “dangerous” when 104°F and above; and you put yourself in “extreme danger” when 124°F and above.

To understand what that means, let’s use an air temperature of 90°F: in 40% humidity, that’s a heat index (“feels like”) of 91°F (“caution”); 90°F and 70% humidity “feels like” 105°F (“dangerous”); and 90°F and 95% humidity “feels like” 127°F (“extreme danger”).

In Los Angeles, I have practiced in yoga rooms where room temperature, after a day of classes, is over 90°F. Even with particularly low relative humidity—40%—the room would still be in the “caution” part of the Heat Index.

The Cooling Response

The body starts the cooling process as it warms up either due to exposure to environmental conditions or because of exercise.

The body begins to sweat in response to the temperature gradient (difference) between the core temperature and the ambient (room or outside) temperature. Consider two ice cubes that have a core temperature of 32°F. “Cube A” is placed in a room that is 60°F, while “Cube B” is in a room that is 33°F. Cube A will experience a greater temperature gradient (difference) between its core and surface “skin,” melting sooner, and faster, than Cube B.

Now add an air conditioning system designed to keep the cubes at 32°F. Cube A’s air conditioner will turn on sooner, and work harder, than Cube B’s.

Recent research has shown there are gender differences: men sweat more than women. Researchers do not have a consensus to explain this difference. Some suggest hormonal differences, others say it’s because women have more surface skin area in relation to their mass, (so there is more surface area to cool via evaporative sweat and other methods), and yet others say that it’s evolutionary: men evolved as hunters so were more active and exposed, while women were primarily gatherers.

I am proposing a new theory to describe thermoregulation differences between individuals, and between genders, and have developed trial protocol to test its hypothesis:

Since men generally have a lower core temperature than women, and men generally have more body mass (fat plus muscle) in relation to their weight, the temperature gradient between a man’s core body temperature and the ambient (room) temperature as measured on the skin increases sooner, and faster, than a woman’s when exercising, especially in hot and humid environments. As a result, men start their cooling response sooner, and must work harder (sweat more) to cool themselves, than women.

And the converse: in cold temperatures, in general, a woman’s heating response will happen sooner, and work harder, than a man’s, because the temperature gradient is greater for women (higher core temperature exposed to colder ambient temperature).

There will be variations across individuals and environmental conditions. For example, most women do not build muscle effectively, but some do. Likewise, there are many men who do not build muscle effectively and excel as marathoners and gymnasts, whereas others build muscle very easily and compete in football, rowing or weight lifting. As a result, they will have individualized cooling responses, but I suggest those responses will follow the general theory here.

I have tracked my body temperature for several years, unscientifically. Generally, my body temperature is 97, and dips into the 96 range at various times. When I walk into a yoga room, usually it’s over 80 degrees and usually it’s humid. As a result, my cooling response starts immediately—I start sweating—without any physical exertion.


The claim that sweat releases “toxins” is largely unsubstantiated. The reason: the main purpose of sweat is to cool the body. While sweat has been shown to contain trace amounts of lead and mercury, urine and feces are the most effective cleansing methods to rid the body of toxins. If you sweat for sweating’s sake and don’t drink enough water, you could actually hinder the body’s job of purifying and releasing toxins.

Sweat also contains over 30 nutrients, minerals, amino acids and enzymes. Profuse sweating can deplete the body of these elements unless they are replenished.

The idea of “purification” stems from the Yoga Sutras. The Yoga Sutras were written about 2,500 years ago. The Sutras do not contain any reference to physical practices or asana. How, then, can “purification” mean “sweat”? Keep in mind that 2,500 years ago, there was no oil pollution, plastics, by-products from fossil fuels, and no food preservatives or additives like Red Dye No. 7 or Blue No. 4 that needed to be expelled from our bodies.

Instead, “purification” in the Sutras is a metaphor. It refers to eliminating the “maya” of the external world. That is the mistaken perception that external objects, i.e. people, places, things, money, fame, etc., can bring us contentment, happiness, or contact with God. These concrete objects seductively provide the false perception that, if we self-identify with them, they will define who we are, provide meaning to our existence, and otherwise fill our existential void.

It seems, then, that some practitioners unwittingly interpret the philosophical idea of “purification” as physical things—“impurities” and “toxins”—that can be removed via physical sensations—“heat” and “sweat”—thereby falling into the very trap of “maya” that the Sutras warn against!

The energetic buzz that many practitioners feel during and after practice is not necessarily related to anything intrinsic or unique to yoga. While it is caused in part by stimulating the nervous system through movement, it is also caused by the body producing endorphins. This is a part of the “fight” or flight” response we developed over thousands of years of evolution. Endorphins ‘numb’ the sensation of physical exertion so that our bodies push beyond its physical limits to defend itself in what may be deadly combat, or to provide the extra “oomph” needed to escape. While endorphins are helpful while fleeing an enemy, they are harmful when they mask pain that is trying to tell us to slow down.

Some Conclusions for Yoga

Yoga studios advertise and cater to a wide variety of participants: men, women, young and old. Many studios shut the windows and doors and advocate the benefits of sweat that results from high heat and humidity. Some artificially heat rooms, even in summer, causing room temperature to soar.

In closed rooms, practitioners’ bodies give off heat, humidity and other waste products, increasing temperature and humidity and decreasing oxygen, making it more difficult for the same people to refresh themselves by inhaling oxygen-rich air and to cool themselves through evaporative cooling. Individuals also vary in their biological ability to cool themselves: older people will have a harder time cooling themselves than younger people, and those with more body mass and muscle will heat up and sweat more quickly than those with less body mass.

Studios should take proactive steps to ensure accessibility for all practitioners. Studios should adopt the NOAA Heat Index Chart so that classes fall below the “caution” stage. A general rule is to limit air temperature to 75°F or less and install air treatment equipment to limit humidity. Another option is to adopt guidelines from the American College of Sports Medicine, which recommends indoor room temperature between 68°F to 71°F when exercising. Some exercise physiologists go further and recommend limiting indoor exercise room temperature to 65°F. One yoga studio uses “Fresh Air Inside,” as a marketing slogan, yet many classes feature closed windows and doors. They should make sure that their claim is actually true.

Yoga teachers and studio owners need to train their employees to watch for signs of hyperthermia, or heat stroke. The first signs are bright red faces and fast shallow breathing. The increased pulse and breath rates of yogis are not always due to aerobic exercise—instead, it could be from the body’s attempt to keep itself cool.

Studios and instructors should not force their personal preferences upon practitioners. Accurate information regarding thermoregulation should be disseminated so that heat-related deaths, like those in Arizona, are not repeated. The idea that “purification” is enhanced by “sweat” to rid the body of “toxins” should be avoided because it is without substantiation, and because too much sweat leads to an imbalance of the body’s nutrients.

Finally, yogis should be tolerant of their fellow practitioners. Unfortunately, too many yogis believe that what their teacher told them is “right,” or that what is right for them (based on their age, sex, body type, and experience) is universally “right” for all seven billion people on the planet. This is not only a false perception of reality, in yogic terms, but it is also egotistical and the exact opposite of a spiritual practice.

Dan Pitkow is currently an entrepreneur in Santa Monica. His first company, Flipper, makes a simple remote control for seniors, and others seeking simplicity in their everyday life and is in the Top 10 on Amazon.com. He studied Classics and Ancient Greek at the University of New Hampshire, before the University of Pittsburgh Law School. Before ‘coming’ to yoga, he was a competitive athlete, winning a high school and collegiate national championship in rowing. He currenlty practices ashatanga, completing the second series, with Jorgen Christiansen, and Tim Miller and Rolf Naujokat. Other yoga influences are Vinnie Marino, Shiva Rhea, and anyone who is teaching a class at a convenient time and location, preferably close to the beach. After leaving law, he travelled through Asia, India, China, Australia, central Europe and Greece. An armchair student of Joseph Campbell, and other science / creation myths, he believes that cross cultural similarities far outweigh their differences.

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