The muscle

How do muscles work?

The body is an amazing machine. In this article, we tell you about how muscles work.

Muscles are one of the most used parts of the body. Their shape is adapted to their role: arm and leg muscles are long, back muscles are flat and muscles around the lips and eyes are circular. Muscles are seen as a symbol of strength and good health, and doing sport is the best way to build them up. In this article, we focus on striated skeletal muscles, muscles which are attached to the bones by tendons.

What is a skeletal muscle?

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.

What is a muscle made of?

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.

How does a contraction work?

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!

How can you trigger muscular hypertrophy?

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: 

Muscles and pain

  • Muscle contracture

    This is a painful and lasting muscle spasm resulting from excessive use. There are different types of contracture:
    • primary muscle contracture: when the muscle is used intensively for a long period without rest
    • muscle contracture with injury: the muscle is physically injured in the case of tearing, stretching or muscle strain
    • defensive muscle contracture: a defence mechanism for an injured joint.

    Muscle contractures mostly affect the calves, thighs, bottom, and neck and back muscles. They are caused by the contraction of muscle fibres.

  • Cramps

    These are random, ongoing muscle contractions. The muscle contracts involuntarily and doesn't relax for a short period, which can last anything from a few seconds to fifteen minutes. This often happens during exercise or at night-time (known as nocturnal cramps).

  • Aches

    These are caused by micro-tears in muscle fibres, as a reaction to which the body triggers a minor inflammatory reaction to repair them.They happen when the muscle is not accustomed to an exercise it carries out. They are generally painful 12 to 48 hours after exercise and last 5 to 7 days depending on their intensity.

To avoid this kind of pain, you must take care of your muscles before, during and after exercise. Tips:
Warm-up and stretching at every sports training sessions.

You also need to tone down your effort and listen to your body when you feel pain.

It's useful to know that heat relieves muscular pain. So there's nothing better than a nice, hot bath after training!

Lastly, hydration is essential, and outside of your sessions, make sure you have a balanced diet that meets all your needs.