The beneficial effect of stretching on the human body.

Stretching is something most people don't do willingly. Athletes who somehow manage to squeeze in an hour or two of training a day never manage to find the extra 5 to 10 minutes they need for satisfying stretches. There are many and varied reasons for this. First, most stiffs are not convinced that stretching is beneficial. Then we are ignorant of what it takes to make it happen. Third, experience has taught us that stretching hurts. And finally, we are tormented by the worry that we might be doing it the wrong way.

Muscles have a complex mechanism that protects them from damage that can be caused by overstretching. Muscles contain microscopic stretch sensors (receptors), which are embedded in the working part of the muscle, the muscle fibers. When a muscle is suddenly stretched, the degree of stretch is sensed by stretch sensors. These send messages back to the brain, via the spinal cord, to the nerves that control the contraction of the muscles on which the sensors are ultimately located (the stretched muscles, that is). As the intensity of the stretch increases, the stretch sensors begin to be stimulated much faster and much more strongly. Eventually, these stimuli exceed a certain threshold and then the stretched muscle contracts and shortens, protecting the muscles from overstretching.

A general rule of thumb is that the intensity of pain caused by a stretch reaction varies with the speed at which the stretch was performed. The faster the stretch, the stronger the pain it causes. Another important stretch reaction, the reverse stretch reaction, causes an exact opposite function to that of the ordinary stretch reaction. The sensors of this reaction are not embedded in the muscle fibers but are located on the tendons of the muscles. These sensors are sensitive to the stress placed on the tendons.

As the muscle contracts, the tension in the tendon increases and the sensors are activated. As in the normal stretch response, these sensors send messages to neurons that control the pain of the muscles they are on. But unlike the usual reaction, where they are activated, these sensors work by blocking the muscle's pain. Therefore, the counter-reaction of stretching provides a protective mechanism against contracting so strongly that it ruptures its own tendons. If the tendon senses that the muscle is contracting too strongly, the tendon's sensors "flip the switch" to stop the contraction. One theory is that inhibition of this response during prolonged exercise contributes to exercise cramping.

How does stretching increase flexibility? When muscles are stretched, they exhibit two characteristics: an elastic substance in the muscle fibers that stretches and relaxation from the tension. Thus, unlike an elastic bandage which immediately stretches to its final length when some continuous force is applied, the length of stretched muscles gradually increases over time with a slow tension. This is similar to the movement of a viscous substance, such as honey. Stress relief occurs when muscle tone suddenly drops after a period of continuous stretching at the same length.

Stretching significantly reduces muscle stiffness, reducing the elasticity of muscle fibers and also reducing muscle tone during the stretch. If the muscles are stretched for 30 seconds daily, these significant changes are maintained and extended, so that the range of motion allowed by the stretched muscles increases.

Ioannis Litsioulis

Physiotherapist - Teacher

Graduate of ATEITH