Although we don't talk about them much, your muscles are essential for running!Does running work out all the muscles in the body? How can you look after and protect these incredible machines if you want to run better and for longer?


1. What Is A Muscle?

Before we talk about how muscles function and how they are used when you run, let's take a closer look at what muscles are and how they contract.

Muscles are tissues in the human body made up of muscle fibres that can contract.

There are three types of muscles:

  • The cardiac muscle, which is the heart muscle, and which is completely autonomous.
  • The smooth muscles found in the organs and the blood vessels that contract involuntarily
  • The striated muscles, which are under voluntary control of the nervous system and are used to make the body move when their muscle fibres contract.


It is these muscles we are interested in when we talk about running. Most of the striated muscles are what we call skeletal muscles because they're linked to the bones of the skeleton.
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They have four fundamental properties:

  • ‍‍Their contractility, which is their ability to contract under the effect of a voluntary or reflex nervous command.
  • Their excitability, which is their ability to react and diffuse an electric stimulation.
  • Their extensibility, which is their ability to extend beyond their original length.
  • Their elasticity, which is their ability to recoil to their original length after extension or contraction. 
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2. How Do Muscles Contract?


Once the order to move is issued by the brain, a nervous impulse is sent to the muscle cells, stimulating the release of an excitatory neurotransmitter. This releases the calcium that is stored in the muscle cell: the contraction is underway!
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There are three types of muscle contractions:

  • Isometric (iso = same and metric = length): The muscle shortens under stress without any joint movement. E.g.: the famous core exercises.
  • Concentric: The muscle shortens, and the distance between insertions lessons. For example, when you run, your flex thigh muscles have to contract concentrically (rectus femoris and iliopsoas muscles) to flex (bend) the thigh at the hip to move forwards. When you lift a weight and contract the biceps, this is also a concentric movement.
  • Eccentric: The opposite happens and the muscle extends. If we take the same example as before, when you run downhill, the quadriceps (front of the thigh) must slow down the forward motion of the body, more precisely at the bend in the knee, which is characteristic of a eccentric contraction. Simply put, it holds back the motion. An eccentric contraction happens at the same time as the muscle extension, which can cause micro tears in the muscle fibres. These micro tears are to blame for any sore muscles you may have 48 hours after your run. In the right dose, these micro tears are essential for muscle adaptation and to help increase muscle strength.
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How Do Muscles Work When You Run?


Each running stride is made up of a stance phase (when the foot is in contact with the ground) and an oscillation or suspension phase.

The stance phase can be broken down further into two phases:

Impact absorption: Your muscles contract to absorb the impact and slow down the body's forward movement. In a way, your muscles, in particular the quadriceps, slow you down in an eccentric contraction. The large and medium glutes also contract to control the forward movement.

The propulsion of the body: At the end of this first phase, the hamstrings (the muscles at the back of the thigh) activate to straighten up the hip just before propulsion begins. Two muscle groups are called upon to propel the body forwards: the hamstrings (four muscles) and the calves (three muscles, full name: triceps surae) that participate in knee flexion and prepare the lower leg for the forward movement.

The tibialis anterior muscle is also active: it is the main muscle responsible for the dorsiflexion of the foot (bringing the end of the foot towards the leg).The abdominal and glute muscles are also used as they stabilise the hip and back joints to allow correct movement of the lower limbs.

In a nutshell, running is a sport that mobilises and works out the whole body. Of course, you have to take care of these muscles and strengthen them if you want to keep running well over the long term.
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How Do Running Injuries Occur?

Studies show that around 50% of runners suffer from at least one running injury. These injuries usually occur around the skeletal muscles (muscles, tendons, joints). A muscle injury is a sign that you have pushed yourself too far, and a number of factors could be at play (training intensity, muscle imbalance, biomechanics, shoes, diet, previous injuries etc.), which runners need to consider.

It's important to know about the different types of muscle contractions and the muscles that are involved in running if you want to work on strengthening these muscles as well as manage the intensity of your training sessions. For example, your muscle-building exercises should aim to strengthen the lower muscles, particularly when the opposite muscle groups are concerned. Exercises involving the quadriceps, for example, should be balanced out by hamstring training. Also remember to strengthen your abdominal muscles to support your back, notably through core exercises. And don't forget eccentric muscle building!

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