Sweating and Hydration.

My girlfriend and I have joined forces on an e-book, geared towards providing anyone walking into a Bikram yoga class, whether it’s their first time or they’ve been doing it for a while, with basic information about how their body functions when exercising in intense conditions, and what they need to know to take proper care of themselves.

(My girlfriend is a professional Bikram yoga instructor—here’s a link to her blog: http://yogamattes.com)

So, we’re writing the book with a Bikram Yoga class in mind, but the basic information in there could be useful to pretty much any kind of athlete. These first two chapters are on sweating and hydration—those are important no matter what your sport or style of training is.

1. Sweating

Well over a century ago, a French physiologist named Claude Bernard (1813-1878) made a very important observation. He observed that body cells survive in a healthy condition only when the temperature, pressure and chemical composition of their fluid environment remains relatively constant. This is still a pivotal observation in modern physiology. We don’t call the environment of cells the milieu interne, like he did—we call it the extracellular fluid. Extracellular fluid fills the microscopic spaces between cells, and it is actually of two types: interstitial fluid, and blood plasma (the fluid part of whole blood, as opposed to the red or white blood-cells.)

The relatively constant state of the cellular environment is called homeostasis. The literal meaning of homeostasis in Greek is “Standing or staying the same.” That doesn’t mean our body’s homeostasis is something that stays the same all the time and never varies, it just means that, while the internal environment will vary, the body will work ceaselessly to keep it relatively constant—because there is a narrow margin for change in our internal environment before the cellular and chemical processes that are the literal basis of life cease to move along properly. As an example, the homeostasis of blood temperature is 98º F, but it will vary slightly above and below that point. For the most part, though, the body has mechanisms in place to keep blood temperature there, even when environmental factors outside the body threaten to change it. Mechanisms for maintaining homeostasis involve the functioning of nearly all the body’s organs and systems. The body has its metaphorical hands full, working endlessly to maintain the constant internal environment upon which its survival depends, adjusting continually to a changing external environment.

Temperature regulation is of the utmost importance, because life depends on various chemical reactions taking place inside the body at a certain rate—and changing temperature changes the rate of chemical reactions. Unchecked internal temperature fluctuation would have catastrophic effects for the body, so there are thermostatic mechanisms in place to maintain—yes, you guessed it—temperature homeostasis. To maintain an even temperature, the body must balance heat production with heat loss—if extra heat is produced, that amount must be lost. Heat loss, primarily, occurs through the skin by the processes of evaporation, radiation, conduction and convection.

And that (finally!) brings us to sweat. Sweat is produced by sudoriferous glands, the most numerous of all the skin glands. Histologists estimate that one square inch of skin on the palm of your hand contains 3,000 little coiled, less-than-0.4-mm-diameter sweat glands. The number of sweat glands all over your body can exceed 3 million. These glands will work throughout life to produce a watery fluid rich in salts, ammonia, uric acid, urea and other wastes—a fluid which in addition to excreting wastes helps maintain a constant core temperature. And obviously, if the replenishment of lost fluids is not adequate, serious dehydration will occur. (In extreme conditions the body is capable of an astonishing sweat-production of 3 liters per hour for short periods—a prodigious rate which will almost always exceed what we can replace by drinking.)

Heat energy must be expended to evaporate any fluid, so evaporation of sweat is a major method by which the body loses excess heat. (When you’re in a Bikram yoga class and your teacher says, “Don’t wipe the sweat! It’s helping to cool you down,” that’s what she means.) The process of evaporation taking place on the surface of your skin is contributing majorly to heat loss. Evaporation is especially important in high-temperature environments, where evaporation is the only means the body has for heat-loss. Radiation and conduction involve the transference of body heat to a nearby surface with a cooler temperature (that’s what happens, it’s just thermodynamics) but in the hot-room during a Bikram class, everything around you is just as hot as you are, so you can’t lose heat that way. Evaporation is literally your body’s only shot at cooling itself down. So, leave that sweat there, and if it tickles a little as it drips down, just deal with it.

A humid atmosphere inevitably retards evaporation, which is why a really humid class leaves everyone flat on their mats, even if the temperature wasn’t any higher than usual. But that doesn’t mean you have no hope for heat loss through evaporation in a humid room: a ceiling fan, no matter how slowly it’s rotating, can be your saving grace. Convection is the transfer of heat away from a surface (for instance, the surface of your skin) by movement of heated air or fluid particles. The moving air, even if it doesn’t feel cooler, will allow your body to lose more of the excess heat than it could in a stagnant atmosphere. So avail yourself to the fan, if possible, even if it doesn’t feel like it’s doing much.

Sometimes your teacher will mention the antimicrobial properties of sweat. That doesn’t mean exactly what it sounds like—your sweat isn’t some natural cleaning product that will leave the hot room, by virtue of the gallons of sweat shed into the carpets daily, a sterile environment which never needs cleaning, where we could safely perform surgery or assemble microchips. But sweat does play a part, along with the sebaceous or oil glands, in maintaining a surface film which covers your skin, providing a protective barrier against bacteria and fungus, hydrating the skin surface, buffering against various caustic irritants, and blocking a verity of toxic agents. So, there’s another reason not to hastily wipe sweat away as soon as it starts to glisten on your forehead.

2. Hydration

All this talk of sweat brings us to a strongly related topic—hydration. Water is lost through sweating, and water regulates your body temperature, lubricates joints, and helps transport nutrients. So obviously you don’t want to lose it without replacing it.

If you’re not properly hydrated, your body simply cannot function at its highest level—and dehydration can lead to fatigue, muscle cramps, dizziness and more serious symptoms.

There are no rules set in stone, when it comes to guidelines for water-intake before, during and after exercise. Everyone is different. And there are a lot of variables affecting water-loss—heat and humidity, exercise intensity and duration, general level of physical “fitness.” Body weight makes a difference, age can make a difference, etc., etc. Your specific need for water is just that—specifically yours.

The simplest way to monitor that you’re staying properly hydrated is to check your urine. Don’t wince, this is science. If your urine is remaining consistently clear or light yellow, you are most likely staying well hydrated. (Before actually walking into a Bikram yoga class, you should be well-hydrated enough that your urine is clear, but day to day, straw-colored urine is ideal.) If your urine is amber-colored or dark brown, it’s a sign that you’re becoming dehydrated.

There are further general guidelines to be found on the internet regarding water intake in relation to exercise, but, again, your need for water isn’t general. It’s specific to you. And a good guideline that’s specific to you is—yes!—your level of thirst. If you’re thirsty, drink. Stop drinking when you’re not thirsty anymore. Then, when you’re thirsty again later, drink some more. Following that golden rule, and also being aware of the color of your urine and learning to “read” it to judge your level of hydration in realtime, will very quickly lead you to an intuitive understanding of how to balance your water intake with water-loss in your own body and life.

The signs of dehydration include headache, dizziness or lightheadedness, nausea or vomiting, muscle cramps, dry mouth, cessation of sweating, and heart palpitations. Signs of severe dehydration include mental confusion, weakness and or loss of consciousness. Obviously, you should seek medical attention immediately if you experience any of those symptoms.

Severe dehydration is no joke.

But over-hydration is also a thing. Hyponatremia occurs when there is too little sodium in the body—as can happen when someone, like an endurance athlete for instance, drinks too much water. Hyponatremia is a rare condition involving swelling of the body-cells with water, including, potentially, swelling of the brain. This is an extreme and it’s rare, but it pays to be aware of it, and aware of the trend of excessive water-intake that can lead to it. Excessive water intake of such a catastrophic, heroically disproportionate level comes from ignoring your thirst-level and drinking to some outside guideline. That is, not drinking because you’re thirsty, but drinking because someone told you how much water to drink, so you think you need to force down that last bottle.

Drink to thirst, keep an eye on your urine. That’s the way to self-regulate your hydration and keep it in healthy parameters.

[Next chapter will be on maintaining blood electrolyte balance.]

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