How do muscles work? How many muscles would you say we have in the human body?

In this article, in addition to answering these and other questions, you will see that it is explained what a muscle contraction is, and what are the different types of muscle contraction that exist . Here you will also find examples of each, through simple exercises or everyday acts.

Muscles and how they work when exercising

Before talking about the different types of muscle contraction that exist, it is necessary to know, in general terms, what a muscle is and what a muscle contraction consists of.

As we well know, people and animals have muscles all over their bodies, which cover our skeleton. Specifically, human beings have about 650 muscles distributed throughout the body or, in different sizes. All of them are voluntary muscles, that is, we can move at will (unless we have some pathology or disease that prevents it).

Muscles are a type of organ formed by a tissue of fibers that contracts and relaxes , depending on the type of movements we make. In other words, muscles allow movement.

A muscle contraction is a physiological process in which muscles develop a certain tension, and shorten or stretch (lengthen); they can also remain the same length, depending on the type of contraction.

Thus, a muscle contraction is an effect on the muscles that implies that their fibres generate tension in themselves ; as we have seen, this tension is produced in various ways, for example when the muscle is lengthened, shortened, moved, maintained at the same length, etc.

Types of muscle contraction

Within the field of bodybuilding and training, we find different types of muscle contraction according to the exercises we perform and the muscles we want to train and strengthen .

Here we are going to talk about the great types of muscle contraction that exist: the isotonic contraction (which in turn is divided into concentric and eccentric), the isometric contraction, the auxotonic and the isokinetic.

1. Isotonic contraction

The first type of muscle contraction is the isotonic contraction, also called heterometric contraction, which is the most frequent contraction when doing most sports .

The term “isotonic” means “of equal tension”. In isotonic contractions, muscle fibers contract and change their length. In this type of contraction, the fibres of our muscles shorten and lengthen .

As we have said, the isotonic contraction, in turn, is divided into two types of muscle contraction: the concentric and the eccentric.

1.1. Concentric contraction

In the concentric contraction, the muscle acts, generating tension, to overcome a certain resistance .

This results in a shortening of the muscle fibers and then a mobilization of some part of the body. To make it clearer, this type of movement would be like “concentrating” the muscle.

An example of concentric contraction would be an act as simple as taking a fork and putting it in your mouth , in which we observe how our biceps swells (in this case, it is a concentric shortening). Another example, this time in the field of sport, would be to do certain exercises with weights, such as curl with dumbbells.

1.2. Eccentric contraction

In eccentric contraction, the second type of isotonic muscle contraction, the opposite occurs as in the previous case. In this case, in the face of resistance, we exert tension on the muscle while simultaneously lengthening it . Simplifying it, it would be like “extending” the muscle.

To illustrate, an example would be to lower the bar to the chest in a bar exercise called bench press (in the concentric phase, we would raise the bar).

2. Isometric contraction

The second type of muscle contraction is isometric contraction, which consists of a static contraction .

“Isometric” means “of equal measure or length”. In this type of contraction, the muscle is static (that is, it neither lengthens nor shortens, its length does not vary, as it does in other types of muscle contraction). In addition, tension is generated in it.

A clear example of isometric contraction would be grabbing a toolbox and moving it around ; that is, we generate a certain tension in our arms, which remain static (to prevent the box from falling). As we see in this example, the muscle fibres of the arms do not lengthen or shorten, but are in a permanent position.

Another example of isometric contraction, in this case in sports (gymnasium) exercises, would be to hold the bar (press bench) for a few moments.

3. Auxotonic contraction

Another type of muscle contraction is auxotonic contraction. In this case, the two previous types of muscle contraction (isotonic and isometric) are combined. That is, for practical purposes: when the muscular contraction begins, the isotonic contraction is produced, and later the isometric contraction is produced.

An example of auxotonic contraction is the stretching of rubber bands (extenders) with the feet together (a type of exercise); in this case, we contract the muscles and hold them in the same position for a few seconds, and then return to the initial position.

That is, we stretch the muscle gradually, and hold it in a certain position for a few seconds. There are many types of exercises to practice this type of contraction (as in other cases).

4. Isokinetic contraction

Finally, the last type of muscle contraction is isokinetic contraction. In this case, there is a maximum contraction of the muscle, at a constant speed, over the entire range of movement of the muscle .

This type of contraction is typical of sports that do not require an acceleration of movement, such as rowing or swimming. As we can see, in this type of sport, it is required to maintain a constant and uniform speed to advance in the water.

To avoid confusion, we must be clear about the difference between isokinetic and isotonic contractions (the former mentioned above). When we perform isokinetic contractions, we constantly regulate the speed of the movement, and exercise maximum tension throughout. However, in isotonic contractions, we do not control the speed of movement, nor do we always exert the same tension during movement.

Bibliographic references:

  • Correa, J.E. and Ermith, D. (2009). Principles and methods for muscle strength training. Rehabilitation and Human Development Text Collection. Editorial Universidad del Rosario.
  • Mora, I.S. (2000). Muscular system. Sabinamora.
  • Vilanova, N.G., Martínez, A. y Monge, A.T. (2007). Muscle toning. Theory and Practice. Editorial Paidotribo.