My girlfriend & I have joined forces on an ebook geared towards providing anyone walking into a Bikram yoga class, whether newbie or veteran, 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, and blogs here:

You can see other sample chapters from the ebook about sweating, hydration, electrolytes and nerves either here on Planet Beast or over at her blog. Most of the chapters we’ve put up have been in order, but now we’re taking it out of order to share some basic information about the role of stretching in health and fitness. Again, the ebook is geared towards Bikram yoga students, but any kind of athlete could benefit from the info.

7. Stretching

Proper stretching has a host of benefits for the body. When done regularly, stretching can help to improve range of motion (ROM,) can help prevent injuries and arthritis, relaxes the muscles, can increase flexibility, improve posture, help prevent hardening of arteries and increases blood-flow. Those who stretch regularly benefit more than those who stretch occasionally, and those who perform a variety of stretching exercises benefit more than those who only perform only one or two. By both those criteria, a regular yoga practice is just the ticket.

Types of stretching

There are actually four different types of stretching: ballistic, dynamic, proprioceptive neuromuscular facilitation, and static. Static stretching is the only kind we do in Bikram yoga class. As the name implies, static stretching is performed by stretching the muscle until a gentle tension is felt and held for a certain amount of time, or until muscular release is felt, without any movement or bouncing. The hold is static. This is an important distinction, because bouncing and moving “to get farther into the pose” is a common mistake made by beginners. This is ballistic stretching, which is an entirely different animal. Ballistic stretching exercises are a thing, but they are not at all like yoga exercises. Yoga poses are not designed to be performed ballistically, hence it is not safe, biomechanically, to treat them that way.

Physiology of Stretching 

To understand the tight, pulling sensation experienced during stretching (called passive muscle tension,) it is necessary to look at the physiology of the muscles themselves, simplified to the aspects most relevant to our discussion. An individual muscle is made up of bundles of individual muscle cells. When you think of a body cell, you might imagine a little round glob with a single nucleus. Muscle cells, however, are different than other body cells. They are long threadlike things, which is why they are also called muscle fibers. They are incredibly thin—10 to 100 nanometers—but they generally run the entire length of the muscle they comprise, and can contain multiple nuclei. So, for instance, the individual threadlike muscle fibers that make up your biceps run the whole length of your upper arm; those that make up your hamstrings run the whole length of the back of your thigh, etc. We’ll see why in a moment.
Inside the outer membrane of the threadlike fiber is an even thinner fiber. This tiny inner fiber is called the myofibril. The myofibril, in turn, is made up of individual microscopic contractile filaments called sarcomeres. These sarcomeres facilitate the movement of skeletal muscles (the muscles that move your skeleton; the ones you use all day every day, whenever you do literally anything.) When the muscle fiber is stimulated to contract, these tiny overlapping filaments pull together. On and on down the chain, they pull together, causing the entire muscle to contract towards its origin point and pull against its insertion point. And because the skeletal muscle is anchored to a freely moving joint, the contraction pulls on the joint and causes its angle to be either increased or decreased, depending on what that particular muscle’s “job” is.

Think of a bodybuilder flexing his biceps. As his elbow bends, the biceps muscle suddenly looks larger and rounder. What’s happening? The microscopic sarcomeres inside the muscle fibers are pulling together and overlapping—rather than resting laid out along the upper arm in a long chain, they are piling up: the muscle is contracting. That same contraction is what causes the elbow to bend. Contracting towards its origin point in the shoulder, the muscle pulls on the opposite end—it exerts leverage against its insertion point in the elbow and causes the straight arm to bend. That’s why each muscle fiber runs the full length of the muscle—so they can exert a pull all the way from origin to insertion.

The cause of the passive resistance felt during stretching was once supposed to be extracellular (in the connective tissues,) but a study by Magid and Law demonstrated that it actually comes from within the myofibrils themselves.

What this means is, when you’re stretching, you’re stretching against the elastic resistance of those microscopic sarcomeres. And due to neurological safeguards against injury, it is normally impossible for adults to stretch most muscle groups to their fullest possible length without extensive training, due to muscle activation of antagonists as the stretched muscle reaches the limit of its normal range of motion. While stretching is highly beneficial to the body, over-stretching is detrimental. The body is wired to protect itself against over-stretching injury, and the upper limits we experience in our flexibility are often not mechanical limits at all but rather due our body’s hardwired resistance to the stretch itself.

Stated another way, some of the increases we see in our ability to stretch with practice are not due to increased capacity to stretch but rather increased neurological stretch-tolerance in muscles. Safe, effective stretching increases stretch-tolerance within a healthy, biomechanically sound range, thereby improving range of motion, better aligning joints and relieving chronic muscle tension. Another benefit of stretching is that it stimulates the production of synovial fluid (the fluid that pads and lubricates freely moving joints.)

Understanding that the passive resistance felt during a stretch comes from within the muscle itself illustrates an important principle in safe stretching: when stretching a muscle, it should be relaxed. Contracting the muscle, as we’ve seen, pulls the sarcomeres together, whereas stretching pulls against those sarcomeres. Thus, attempting to stretch a contracted muscle is physiologically unsound, because the muscle will be physically unable to stretch and the tension will be transferred to surrounding connective tissues. Ligaments and tendons do benefit from gentle stretching, but yoga poses are not designed to safely allow connective tissue to bear the full brunt of the stretch. That is not the intended effect of any pose. And yet, stretching against tight, contracted muscles tends to transfer the brunt of the stretch in exactly that way, potentially making the pose more conducive to causing soft-tissue injury. In short, you’re doing it wrong.



Electrolytes and Nerves

My girlfriend & 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 yoga teacher, and blogs at: )

You can see the chapters on sweating and hydration in older posts, on my blog or hers. Again, these are chapters from an e-book geared towards hot yoga class, but the information in it is applicable to all kinds of athletes. We’re writing this guide from our experience in hot yoga, but we’re not just hot yogis—we’re hot no matter what we’re doing. (Har, har. See what I did there?) Anyway, here is some basic information about maintaining electrolyte balance, and what those electrolytes are actually doing in your body.

Chapter 3: Electrolytes

Balancing your hydration level is about more than just water. When thinking about sweat-loss and water intake, you also need to think about electrolytes. Your body’s nerve reactions and muscle functions depend on the proper concentration and exchange of these chemicals.

What exactly are electrolytes? Chemically, they are substances that ionize in solution (that is, dissolve in water) and acquire the capacity to conduct electricity. Some of the specific ones that are commonly measured by doctors are: sodium, potassium and chloride. These substances are lost through heavy sweating—and if you rehydrate with only clear water, then your electrolyte levels will be thrown out of balance; the ratio of water to electrolytes in your body will be altered.

Sodium is a majorly important positive ion in the fluid outside of cells (the interstitial fluid, like we talked about above.) The chemical notation of sodium is Na+. You know sodium best after it’s been combined with chloride—that’s the chemical composition of table salt.

Sodium regulates the total amount of water in the body, and the transmission of sodium into and out of individual cells plays a vital role in critical body functions (as we’ll see when we talk about nerve impulse conduction below.) Many, many processes in the body and brain require the conduction of electrical impulses for communication, integration and control, and the movement of sodium (a positive ion) is essential in generating these electrical signals. Therefore, too much or too little sodium leads to cell malfunction.

Potassium is a major positive ion found inside of cells (it’s chemical notation is K+.) Proper potassium level is essential for normal cell function—among many other things, it regulates heartbeat and the function of the muscles. A serious disruption of potassium levels can critically affect the nervous system and increases the risk of irregular heartbeats (arrhythmias.)

Hypokalemia is a decreased level of potassium. It can be brought on by kidney diseases, or excessive loss due to vomiting, diarrhea, or—most relevant to our subject—heavy sweating.

Chloride (Cl-) is a major negative ion found in the fluid outside of cells and in the blood. It is closely regulated by the body, and plays a role in maintaining a normal balance of fluids. Just like all the other electrolytes, it can be thrown out of balance by various diseases, but, relevant to our discussion, excessive loss can occur through heavy sweating.

Symptoms of Electrolyte Imbalance

An electrolyte imbalance can create a number of different symptoms—and the specific symptoms that manifest will depend on which of the electrolyte levels are affected. Altered potassium, sodium, magnesium or calcium levels can lead to: muscle spasm or cramping, weakness, twitching and convulsion.

When the levels are low (the more likely scenario in a Bikram Yoga class, as opposed to high,) it can cause: irregular heartbeat, confusion, blood pressure changes, headache, dizziness and nausea.

In a hot yoga or Bikram Yoga class, by far the most common signs of electrolyte imbalance will be headache, dizziness, nausea, and cramping.

Replenishing Lost Electrolytes

So we know now that these ionizing substances are essential for a host of critical body functions, and that they are lost during heavy sweating, potentially, and very likely, to the point of excess. So the next step, logically, is to replace the lost electrolytes and maintain the balance. The best way to do that is with consistent intake of electrolytes.

A good rule of thumb to follow: drink your water with electrolytes. Don’t just chug clear water before, while, and after sweating heavily—replenish your lost water and your lost electrolytes together by adding sources of electrolytes directly to your water. As one example: try clear water with added raw honey to taste, a pinch of unrefined salt, and freshly squeezed lemon juice. Take this concoction with you into class—steadily replete both your electrolytes and water together, even as you deplete them through sweating.

When, during or after class, you need an extra boost of electrolytes, supplementation is appropriate. If you experience symptoms of electrolyte imbalance as you practice, you should seek out some concentrated source, such as electrolyte-replenishment packets (like “Emergen-C” or “Ultima,”) or simply a small pinch of sea salt dissolved on the tongue.

Meanwhile, take electrolytes in steadily through diet in your daily life. Don’t rely on concentrated supplementation alone. What that means is, if you do something that causes you extreme electrolyte depletion all the time—like sweating heavily in a Bikram yoga class several times per week—take the initiative. Take steps to prevent imbalances in the first place. You should always be attempting to take in replacement electrolytes at a steady pace throughout your daily life—not only in occasional concentrated mouthfuls after you have already realized the balance is drastically off. This is done through a diet rich in electrolytes. For instance, you know you’re going to consistently lose potassium through sweat in class—so take it in just as consistently, from dietary sources like bananas or coffee. Or whatever—just find sources that work for you and make electrolyte replenishment a dietary priority.

Electrolytes should be taken in in the same consistent, gradual, measured way that you supply your body with water. You know you lose a great deal of water in class, so you consistently take in reasonable amounts of water during the day, every day. In other words, you keep hydration in mind even when you’re not dehydrated. In the same way, keep electrolyte balance in mind, even before you experience symptoms of imbalance.

Extra Notes on Sodium

Sodium warrants special attention for a couple of reasons. One, it is among the main electrolytes lost in sweat (hence sweat’s salty taste.) Two, you generally don’t get much of it from commercially available electrolyte drinks and powders. As a result, you may be taking in a healthy amount of other electrolytes, but, because you are losing so much through sweat and taking in so little through electrolyte drinks or powders, you may still fall short of replenishing lost sodium.

General medical guidelines for low sodium levels recommend restricting fluid intake in order to prevent hyponatremia (too little sodium in the body, relative to water,) but in the context of Bikram Yoga practice, limiting fluid intake is not appropriate. That guideline is general, and does not apply to anyone who regularly loses huge amounts of water through sweat. In the case of low sodium-concentration brought on by massive loss through sweating and dilution by clear water intake, the solution is, logically, increased intake of sodium. A pinch of salt on the tongue, a pinch of salt added to your water, a sprinkling of salt on your food after class. However you take it in, you will need a little boost of sodium to properly replenish what you lose while practicing, before you’re ready to go into the room and sweat again.

Special Concerns 

Certain medications may cause electrolyte imbalances, such as: chemotherapy drugs, diuretics, antibiotics and corticosteroids. If you are on any of these medications, it is important to keep track of your electrolyte levels. Make sure your doctor knows you are practicing hot yoga and understands how much heavy sweating is involved.

Chapter 4: Nerves

Electrolytes are essential for generating the electrical impulses that facilitate the nervous system’s communication and control. How exactly does that work? We’ll take a short, simplified look at it, to a) illustrate how the electrolytes we’ve discussed actually function by conducting electrical impulses and b) to set the stage for the next chapter, wherein we’ll look at the nervous system. There are two main types of cells in the nervous system—neuroglia and neurons. Neurons are the one we’ll be considering here. They can be afferent (conducting impulses towards the brain) or efferent (conducting impulses away from the brain.)

A neuron consists of a cell body (also called the soma or perikaryon,) the axon, and one or more dendrites. The dendrites of a neuron are processes that stick off and branch like tiny trees (in fact, the name comes from the Greek word for tree.) The dendrites receive impulses to conduct from other neurons. Once received, the impulse travels down the axon—a long process, like a thin tail—and reaches the next neuron by way of terminal branched filaments called telodendria. Axons can vary in length from a meter long to a few millimeters. They also vary in width—from about 20 nanometers down to a single nanometer.

In order to understand how impulse conduction works, and how electrolytes are involved, it pays to get familiar with a few relevant terms.

Potential difference—an electrical difference, or an electrical gradient. A potential difference is the difference between the electrical charge present at two points. A potential difference is a form of potential energy. It is a force that has the potential to move positively charged ions down an electrical gradient, that is, from a point of higher positive charge to a point of lower positive charge.

Polarized membrane—a membrane whose outer and inner surface have different amounts of electrical charges. Basically, a potential difference exists across a polarized membrane.

Depolarized membrane—a membrane whose outer and inner surface have equal amounts of electrical charge. A potential difference does not exist across a depolarized membrane; it is zero.

When a neuron is not conducting, the inner surface of its membrane is slightly negative to its outer surface. There is a potential difference across its membrane—in a nonconducting neuron, this is called “resting potential.” The mechanism that creates this resting potential is primarily a sodium-potassium pump, built into the neuron’s plasma membrane (the outer membrane of the neuron.) This pump actively transports positive sodium and potassium ions through the plasma membrane in opposite directions and at different rates. For every 3 sodium ions it moves out, it moves 2 potassium ions in. If, for instance, it pumped 100 potassium ions into a nerve cell from the extracellular fluid, it concurrently pumps 150 sodium ions out of the cell. This makes the inner surface of the neuron’s membrane slightly less positive—or, slightly negative—to its outer surface.

Blamo—there you have the potential difference in a nonconducting neuron known as resting potential. Now, an impulse comes along for the “resting” neuron to conduct.

1) When a sufficient stimulus is applied to the neuron, it vastly increases the permeability of its membrane to sodium ions at the point of stimulation (it lets more sodium in.)

2) The positive sodium ions rush in towards the point of stimulation. The excess of sodium outside the membrane, therefore, diminishes. It quickly reaches zero. In other words, the stimulated point of the membrane is no longer polarized. But only for an instant. Quickly—within milliseconds—the positive sodium ions streaming in create an excess of sodium inside the cell and trigger an action potential. An action potential is a potential difference across a neuron’s membrane with the inside positive to the outside. So, since resting potential has the inside negative to outside, action potential is a reverse polarization. The inside becomes positive to the outside. Development of action potential at the stimulated point of the neuron marks the beginning of impulse conduction.

3) A chain reaction occurs. The action potential of the stimulated part of the membrane becomes the stimulus for the adjacent part of the membrane, and that next stimulated point goes into the same process. The action potential moves along the length of the neuron, point by point, conducting the electrical impulse on to its destination.

[Next up, the nervous system and the fight-or-flight response.]

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:

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.]