What can we learn from the Cybex test for (professional) soccer players? Or not learn?

Cybex! What’s that?

The ‘Cybex test’ is a test which is currently being implemented by hospitals, universities, rehabilitation centers, … . During the test you sit on a chair and variations in force are measured in front side – back side of the leg (Quadriceps – Hamstrings – ratio) and front side – back side of the trunk (abdominals, back muscles).

Purpose of the Cybex measurements?

The intention is to locate the differences and imbalances and it would also help in predicting injuries.

As the picture shows, one is firmly attached to a chair and during the leg test one is supposed to extend the leg (Quadriceps) and bend the leg (Hamstring) against a resistance. A software program measures the results and displays the differences and attention points. This test is applied (mainly) to professional athletes and a lot of professional soccer players with injuries.
In order to better understand the usefulness, the functioning and the conclusions of the Cybex test, let’s take a closer look at the operation of this machine and its test protocol. For the fans or the ‘believers’ of the test, it will be confronting (our apologies); however if we wish to make progress in assisting our athletes, we have to face it in order to achieve the best results.
Here we go!

Muscle Isolation

A first question: why would we isolate muscles (one element in a muscle chain) to measure them? When we look at how the body works, especially when playing soccer, we see that the muscles work together to execute a certain task. When jumping, running, kicking, tackling, … the movement ALWAYS includes the activity of several muscles. The timing of this functioning will be essential to perform sports safely. In other words we benefit big time when we train ‘movements’ and not muscles. This approach is often very different than we are used to; however by introducing ‘functional’ training, we return to more natural movements and logic.

So what do we learn by isolating and measuring separately one’s Quadriceps and Hamstrings?

Muscle Function

How do Quadriceps and Hamstrings function when playing soccer?

Perhaps one of the biggest mistakes we ever made in studying the anatomy and muscles is the use of a corpse instead of a living person.
What is the difference in muscle activity between a corpse and a living person?
If we pull the Hamstrings of a corpse in prone, we notice that the heel moves towards the buttock. At that time they concluded that the Hamstrings bend our leg and are also able to do that while seated and in stance. However it appears that the function of the Hamstrings when eg playing soccer (and of any living / moving person) is completely different. The Hamstring will extend the leg (which is the opposite of what we always thought), become active when bending forward (eg when landing after a jump), when turning the knee inward and outward and when moving the hip laterally.

Question: if we know that muscles function in 3D (3 plans: front-rear, lateral, rotations), which 2 plans do we miss if we only bend-extend in the Cybex test?

Question: if we know how Hamstrings and Quadriceps function when playing soccer (in stance), what will a measurement while seated teach us?

Eccentric instead of concentric functioning of muscles

Probably those words don’t tell you much if you are not medically trained so to summarize, eccentric stands for stretching the muscles, separation of the tendons and concentric for shortening the muscles, closing the tendons. These are two opposite situations in which a muscle can function and as you might expect, combinations are also possible but we won’t discuss them here due to the complexity.
The fact is that muscles respond and develop their strength from the extended / eccentric position. They are not only initiating movement but also brake movement. If they brake movements, they also end up in the eccentric phase. Training muscles from their eccentric phase does not only improve the muscle strength, it also serves as a powerful advantage in injury prevention because many muscle injuries occur due to an unusual or unexpected extension. If you eg want to kick a ball, you will swing your leg backwards first in order to develop your power from there. If you want to head for the ball powerfully, you’ll also move your trunk backwards first and develop the forward force from there. Because muscles and nervous system respond very actively to this eccentric phase, we are particularly interested in the areas where the stretch arises. Our approach of injury prevention (muscle injuries) is in function of this principle.

When do the body and the muscles end up in an eccentric phase during the Cybex test? Don’t we measure only concentrically while when playing soccer the concentric muscle function is preceded by an eccentric ‘load’? If you want to know your blood pressure, you don’t measure the heart rate, right?

Muscles react differently according to their starting position!

We already mentioned that it’s not logical to test a soccer player (who plays soccer in stance) while seated, because muscles function differently in stance compared to seated position. On top of that, a sitting position will switch off the buttocks, the foot is no longer touching the ground, the calf is not functioning and when stretching the leg extensively (Quadriceps) an excessive force is developed on the patella (knee cap) while in stance and when stretching the leg extensively, the force on the patella is rather minimal.
What message do we give the tested soccer player when the Cybex test indicate that the Hamstrings are too weak?
Logically, the soccer player will train the Hamstrings, right? He will do that in a way which will yield a better result next time, no? Meaning, sitting on a chair, pulling the heel to the buttocks against a resistance? Or prone position, same thing? Or Lying on the back, eg pulling a fit ball towards you?

We are confident that the results of a re-test will be better, but is this useful when playing soccer, when the Hamstrings are active in 3D, where the position of the foot, knee and hip will influence the Hamstrings, where the Hamstrings and the Quadriceps have a different function compared to a sitting position, where they develop their strength from contraction to stretch, where in every movement also other muscles control that movement and where there is no isolation at all?


There are to date no casualties yet due to the Cybex test; however we are convinced that our time (and investment) can be used more efficiently and that we probably can come to a more logical assistance in injury prevention, training and rehabilitation. In any case the developments in functional training bring more logic into our approach.

The foundation: Functional Anatomy

There is an urgent need to update our education and adapting the classic anatomy (based on a corpse) to the functional anatomy (of a body in motion). Understanding the basic principles of biomechanics and human movement are necessary to assist our (top)athletes in a way that they deserve!

Soccer DVD : Injury Prevention and Strength Training by Mobility and Flexibility


Over act2prevent

Kinesitherapeut & personal trainer van opleiding, gek op persoonlijke ontwikkeling en sporten. Mijn passie is voetbal en andere balsporten. Hou van duiken en genieten van het leven. Sinds eind 2014 gestart met een eigen voetbalschool voor talentvolle spelertjes geboren in 2008 en later. Wij bieden met de voetbalschool extra trainingen aan tijdens 'vrije' momenten net als een complete 'interne' opleiding.
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