How Stretches Work – The Mechanics of Stretching

| June 20, 2013 | 1 Reply

As mentioned here, stretching is a form of physical exercise that is used to flex and extend the muscles or the tendons of the body so as to produce greater flexibility and wider range of movement. But how does this technique work and what is actually the mechanism behind it?

The Function of the Muscles

Before we get to present the way stretching works, it is essential to provide some basic data on the function of the muscles. The muscles consist a part of the musculoskeletal system along with the tendons (by which actually muscles are attached to the bones), the ligaments and the bones; the muscles are the only component of the system that enables your whole body move, achieving than motion through contracting and, thusly, through generating tension. So, applying external force through stretching will, roughly speaking, make the whole muscle extend its range of motion and become more flexible.

In fact, the crucial factor for achieving a greater range of motion is the elongation of the soft muscle tissue, plastic and elastic. The former refers to the permanent elongation of joints, ligaments and tendons because it remains even after the stretch is withdrawned, while the latter has to do with the temporary lengthening of the muscle tissue, since it rebounds when the stretch is over, and results in extensibility, that is the ability to stretch muscles. In accordance to this, it has been showed that the greatest amount of resistance to stretching comes from the connective tissue framework that is inside and around the muscle and not from the muscle itself.

The Structure of the Muscles

In addition, the nature of the muscles is a little more complex, as muscles are not something unified; they practically consist of smaller strands of tissue, the fascicles, which in a lower level are composed by muscle fibers (photo 1), and these in turn are also comprised of even more compact parts (the myofibrils). Myofibrils also are comprised of smaller units, the myofilaments. Myofilaments are divided into two types, thick (comprised of myosin) and thin (comprised of actin)! These structures are composed of repeating subunits called sarcomeres, while the latter contain lengthy and fibrous proteins  that are overlapped each time the muscle contracts and relaxes. Photo 2 shows the structure of the Muscle Fiber while Photo 3 clearly shows the parts of a sarcomere. Finally, it should be mentioned here that the all the parts of the muscle system are connected by tissues and dipped into lubricants, to accomplish their mission of moving the body each time the brain commands them to do so.

Structure of Muscles

Photo 1 – Muscle’s Structure

Muscle Fiber StructurePhoto 2 - Muscle Fiber Structure

Photo 2 – Muscle Fiber Structure


Photo 3 – Sarcomere Structure

What Exactly Happens When a Muscle Stretch Is Performed?

When a muscle is contracted, the thick filaments start pulling the thin ones to the center of the sarcomeres, which is actually the basic unit of contraction. An overlap between the thick and thin myofilaments is initiated, becoming bigger as the stretch is developing; when the sarcomeres stretch, the overlap area diminishes and the muscle fibers elongate. When every sarcomere is completely extended, the muscle fibers have reached the largest degree of their resting length as well, so extra tension is all directed on the adjoining connective tissue. Maximizing the tension forces the collagen fibers in the connective tissue to be lined up with the tension. At the same moment  the disarranged muscle fibers straighten up in the line of the tension, and that is absolutely vital for your tissue’s restoration (especially after a strenuous work-out).

What happens when stretch is performed

What happens when stretch is performed

Stretch Reflex

A notable mechanism of the body is the stretch reflex (or myotatic reflex); that means that your body spine is able to detect abrupt and uncontrolled changes in the length of a muscle through the signals that muscle spindles (sensory receptors inside the muscle) send and resist the change in muscle length by causing the stretched muscle to contract, thus protecting from unwanted injuries. However, you can “mislead” that function by stretching regularly and progressively so as to force the muscle spindle to get used to a continuously increased length and ultimately achieve a larger range of motion. The steps of the Stretch Reflex can be seen on the image below:

Stretching Reflex

Stretch Reflex

The Importance of Stretching for Athletes

The above presented become even more important for an athlete or a person who works out with weights as stretching can speed up the recovery process by not only lining up the twisted muscle tissue but also by boosting the blood flow (which increases cells nourishment, eradication of byproducts of cell metabolism etc)! Therefore, even if you are not convinced about the usefulness of stretching in the ordinary daily routine, there is really no excuse of not performing a bunch of stretches on the body part that has been worked out, before your it gets back to a relaxed state; finally we need to notice that the warm muscles and joints are the best guarantee that no injury or inappropriate tension will occur to muscle fibers.

At this point, we need to notice that even more benefits (that don’t exclusively refer to athletes)  are directly connected to stretching. You can discover them in our detailed article on stretching benefits.

Our Opinion

Now that the mechanism of stretching has been adequately explained, the precondition of consulting your doctor before beginning it may seem even more vital if you want to actually benefit from this technique and stay away from potential injuries. Of equal importance is also the performing of the stretches under supervision from a skilled trainer (at least, during your earliest attempts), since implementing the right techniques, avoiding over-stretching and choosing the most appropriate techniques can signify the difference between a beneficial outcome and a worthless – or destructive – result.




Category: About Stretching

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