How do muscles work?

DID YOU KNOW?Our bodies are made up of over 650 muscles classified into 3 major categories: cardiac muscle, smooth muscle (under involuntary control) and skeletal muscle that enables us to make movements by voluntary contraction.

Striated skeletal muscles are the most visible and we have over 600 of them. They give the body its appearance and their total mass accounts for over half of an adult's bodyweight. Striated skeletal muscles are responsible for our voluntary movements since they contract when we ask them to do so. They also enable us to control our posture and maintain and move our joints. In weight training, the focus is mainly on skeletal muscles, which account for about 40% of total body mass.

A muscle is made up of a multitude of cells called muscle fibres. These are grouped into bundles to make up fascicles, which are supplied with the energy necessary for the fibres via the blood vessels.

Muscle fibres can measure anything from just a few millimetres to over 10 centimetres. They contract thanks to threadlike structures called myofilaments, that make up the myofibril. The filaments slide against each other during effort by tightening. Thus, the muscle contracts then relaxes and so on.

It should be noted that myofilaments are composed of 2 different types of molecule:

• actin (a very thin filament)

• myosin (a thicker filament)

These two types of filament are responsible for contractions.

Muscles are simply a tool that enables a contraction to take place. It's actually the brain that gives the command and decides to contract a muscle.

When we decide to execute this action, we order the brain to send a signal to the muscle. The motor cortex is the area of the brain that receives the order. It receives information from various regions of the brain that give the direction or speed of a movement, etc. The cortex analyses the information and translates it into a nerve impulse that it sends to a neuron. The electrical signal generated by the nerve impulse travels along the nerve channel.

The nerve impulse has to go through a number of stages to get to the muscle. So, in the upper part of the spinal cord, a second neuron, known as a motor neuron, takes over and reaches the muscle so that the nerve impulse stimulates it. The motor neuron is divided into many nerve endings at the tip and each of these endings enters into contact with the muscle fibre. The association of a motor neuron and fibres is called a motor unit.

Furthermore, the meeting point between the motor neuron and the fibres is called the neuromuscular junction. This is where the electrical signal triggers the liberation of chemical molecules, the famous neurotransmitters.

This is when a sequence of electrical phenomena take place that enables the liberated molecules to travel to the filaments so that they contract. This takes place simultaneously in numerous muscle fibres dispersed throughout the muscle.

After all of this, here we are with a muscle that works!

When you weight train, you impose great effort on your muscles via extra weights or bodyweight in order to increase strength, endurance or muscle volume.

To trigger hypertrophy, you need to follow a very specific number of series, repetitions, loads and frequencies. Check out our full article on hypertrophy: