News No Comments 8 March 2018

BASIC PHYSIOLOGY OF MUSCLE CONTRACTION

So far we have talked about training techniques, food and supplementation strategies to improve performance and appearance. I’D LIKE to get a little more behind the scenes, going to see what runs what and more importantly, how.

LET'S START WITH THE BASICS, THE STRUCTURE OF MUSCLE

Striated muscle is made up of a series of cellular elements in an almost cylindrical form, of considerable size, called muscle fibre. These are aligned in parallel bundles and are independent from each other. Each fibre is coated with a plasma membrane called sarcolemma. The sarcoplasmic reticulum (this is the name of the endoplasmic reticulum of muscle fibres), wraps up groups of filaments, arranged in parallel and called myofibrils. Each filament consists of a large number of sarcomeres arranged in series, which represent the muscle contractile unit. Sarcomeres consist primarily of filaments formed primarily by actin and myosin.

THE MECHANISM OF CONTRACTION OF SKELETAL MUSCLES

Muscle contraction occurs due to the sliding of actin filaments on myosin ones. Sites of myosin heads can bind to actin filaments forming the so-called actin-myosin bridge. Subsequently, the myosin head rotates toward the centre of the sarcomere dragging actin along and causing the two strands to slide (this movement is called "power stroke"). Once the movement is over, the two strands separate and everything goes back to the initial stage.

THE ROLE OF THE NERVOUS SYSTEM

Muscle contraction is controlled/ordered by the nervous system, in particular by a motor neuron, which sends an electrical signal to the muscle, triggering a "tot" number of fibres and releasing the chemical mediator acetylcholine (Ach). The cascade of events that follows is called "Excitation-Contraction Coupling” and causes a whole cascade of events so that the end result has the above-described mechanism (with various specific intermediate steps that I am not to deal with now) .

THE MU (MOTOR UNIT)

The body, though, does not reason by "fibres" but by "motor units" according to the law called "all or nothing". A motor unit consists of a motor neuron and all of the muscle fibres it innervates. The number of muscle fibres of a MU is highly variable and can go from 5 to 2000 or more. A motor unit cannot turn on only part of the fibres it controls; in fact, when a motor neuron launches the impulse, it will activate and contract all the muscle fibres it controls: we talk about thresholds of excitement where, above a certain threshold, some “larger and/or stronger” MUs are activated. How many MUs get activated? It depends on the load applied. From 85% upwards of their ceiling, all MUs of the target muscular district will be active. On the other hand, the fluidity and continuity of the contraction is controlled and guaranteed by the asynchronous and staggered activity of the motor neurons that determine the MU’s alternate contraction, so while "half" work, the other "half" are resting and so on. This until the energy reserves of the energy metabolism used are exhausted.

I hope the article may be of interest to you and I invite you not to stop, because only by knowing the principles, we really master the methods. I am available for any info or questions.


Author: Mattia Lorenzini – Personal trainer, expert in sports nutrition and author of the CorporeSano – Food&Training System informative project (corporesanofitness.com)DISCOUNT CODES

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