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Muscle contraction and relaxation

One of Systema pillars is relaxation. However our idea of relaxation differs from many common practices. The relaxation we seek is not passive, flaccid. Let’s talk a little more about the characteristics and the physiology of the muscles, to have it clear why the active relaxation is important for the practice of Systema. The muscle fiber or the muscular cell, is composed of many filaments called myofibrils. The myofibrils are actin and myosin filaments that are organized parallel to each other. When the muscle contraction occurs, these actin filaments and myosin overlaps, or slide over each other, causing the cell to shorten. Thousands of muscle fibers acting at the same time will result in the movement. But for this overlap occur it is necessary that calcium ions enter into the cell (calcium ions interact with a troponin that “hides” myosin from actin. As the actin and myosin have a very strong attraction, troponin prevents constantly interacts between them, when there is calcium, it reacts with troponin leaving a bridges for actin and myosin interaction).

But for calcium ions enter the muscle cell, a neurotransmitter that is released by motor nerves, acetylcholine, need to open ion channels that allow the entry of calcium. Calcium is also stored inside the cell in a structure called sarcoplasmatic reticulum. When calcium enters the cell it stimulates the reticulum to release calcium that is stored and contraction occurs. All this happens in milliseconds.

An important aspect is that the more muscle fibers were activated, the greater the capacity to generate force (voltage) of that muscle. Who coordinates how a muscle will contract are motor nerves through the motor plates. The motor end plates, or myoneural joints correspond to the union of muscle fibers and motor nerve. So when a nerve receives an impulse, it releases acetylcholine in the motor plate that allows the entry of ions calcium in the muscle cell. A single nerve fiber may innervate a single muscle fiber and then ramify and innervate up to 160 muscle fibers. Who controls the degree of contraction intensity is the nerve cell that decides how many muscle fibers it will activate. Typically the muscles that need a greater amount of control and sensitivity for movements, such as the muscles of the hand, has a single nerve fiber that will innervate a single muscle fiber, whereas in larger muscles nerve fiber will branch.

However, to be a proper tension, there must be space for the sliding of myofibrils (actin and myosin). The tension developed by the muscle contraction depends on muscle length for sliding. The maximum voltage is achieved when the muscle is in great length, the resting length and decreases as the muscle is elongated or shortened (over-voltage). When the muscle fiber is in the resting length, this means that all connection points between the actin and myosin are free. When there is a gap between the filaments, the tesion decreases because there are fewer connection points. The further there are, the less points they will have to interact until there’s no more connection points and the muscle won’t be able to generate tension. When there is a shortening of the muscle fiber, a filament overlaps and interferes with the binding points between the actin and myosin, thereby reducing the tension.

contração muscular

We aim to achieve the third fiber leght (from left to right) that can generate the best tension/strength 

An event such as trauma or excessive acetylcholine release in mioneural joint can result in excessive calcium release from the sarcoplasmic reticulum leading to muscle chronic contraction. When a muscle is chronic contracted, there is a reduction in blood flow, which reduces the energy supply to and induces a failure in reception of the calcium to the sarcoplasmic reticulum, favoring the cycle to continue. Thus contracture can remain stable or increase.

A consequence of muscle contraction is the joint contraction of the connective tissues that surround (endomysium, perimysial and epimysium) which will limit the movement of nearby joints. Imagine someone is pulling your shirt down and you try to lift the arm. You can perform the movement, just need more power to do this. This also decreases blood flow and causes muscle to fadige faster. For Systema it is important to have a muscle relaxation to improve the power of an attack, allowing the joints to move throughout its range and ensure there is an adequate blood supply to the contraction. So we work to relax the body mainly in the deep muscles that usually store a lot of tension.

For Systema it is important to have a relaxed muscle in order to better generate strength, to allow the joints to move free and to guarantee an adequate a good blood supply for the contraction to occur. That’s why we work to relax ours muscles, especially the deep ones that normally stare a lot of tension.

26/07/2017

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