Stretching

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: http://yogamattes.com.)

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.

References:

http://www.ncbi.nlm.nih.gov/pubmed/4071053.

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