Leg flexor - What does it actually do?

The leg flexor - a muscle often misunderstood.

In order to optimally train an individual - regardless of whether he or she is a competitive athlete, amateur athlete or normal client - a fundamental, functional understanding of the living human being is indispensable.

The basic function: Moving upright on both legs

Only those who understand how a person should move in a situation and how they actually move can develop functional strategies from this. A look at anatomy books shows that humans seem to move only in a sagittal axis. Frontally and transversely, they describe muscles - if at all - only very statically.

The most important function of a human being is not to lie or sit on the stomach, back or bottom, but to move around. And in the most effective way: upright on both legs. In this functional movement it is useful to keep in mind the task of the muscles. Because from this a specific and sport-dependent consideration is possible.

Walking as the most important functional exercise

The example leg flexor

Even the naming shows how isolated this muscle has been considered so far. Sure, it bends the leg when standing or even lying down. But who has ever strolled along a street and deliberately bent the leg flexor?

Gym goers lie in the prone position on a "leg curl machine" costing several thousand euros. Such a device is extremely effective for muscle building, but not functional. Two things are missing: the frontal and the transversal axis. So, in that sense, there would have to be three different leg curl machines to complete the movement. Because every joint in the human body, without exception, functions in three axes and should be moved and trained in all of them from a functional point of view.

Stretching the back of the leg with stretchme technique

A little more precisely: The leg flexor or better hamstring - like all other muscles by the way - does not work in isolation, but is part of a whole muscle group. The group consists of semimenbranosus and semitendinosus (the two inner/medial heads), as well as biceps femoris with the long and the short head as the two outer/lateral heads. The first three attach to the pelvis at the tuber ischiadicum. The biceps femoris with the shorter head originates at the posterior part of the femur. The semimenbranosus runs to the medial part of the tibia and the soft tissues of the posterior medial part of the knee. The semitendinosus runs more to the anterior medial portion of the tibia, but the biceps femoris runs to the outer portions of the fibula head (fibula).

The leg flexor elongates

Based on the origins and approaches of this muscle group, it can be guessed that a purely sagittally oriented mode of operation cannot be the goal at all. Due to its attachment to the pelvis and a relative movement of the pelvis to the thigh in the frontal plane, the hamstring is directed in adduction and/or abduction. Does this also make it a hip commuter?

On the lower leg, it seems like the hamstring just wants to transversely hug the lower leg from behind. Does that make him the knee twister now too? When we are about to put the left foot in front of the right, the pelvis tilts forward. This means an elongation of the hamstring at the hip joint, i.e. those three heads that attach to the pelvis.

Lengthening is the "load", the eccentric stretching of muscles in preparation for the concentric phase ("Explode"). When our left heel hits the ground, the knee bends due to the force of gravity of our own weight and our own acceleration.

Functional partner exercise for the back of the leg
So who bends the knee? Gravity and not the leg flexor! Knee flexion is done by Mother Nature's natural conditions. Once again, the hamstring stretches at the hip joint. So it elongates. At the same time, there is knee flexion, which is a shortening of the hamstring at the knee joint.

The leg flexor works exconcentric

Anatomy books know exactly three possibilities for the working of the musculature:

  • concentric
  • eccentric
  • isometric

But how does the hamstring actually work according to the above description? 

In the sagittal plane during a forward movement: EXCONCENTRIC!

Here's what happens in the frontal plane:

When the heel hits the ground, a pronation of the foot and the resulting upward chain reaction will cause the knee to fall inward. When viewed from the front, the knee experiences abduction (valgus). The muscles running on the inside of this knee (and of course ligamentous apparatuses) slow down this abduction and promote an emerging adduction (load to explode).

In the third, the transversal plane, the following takes place:

As the heel pronates when the front foot hits the ground, the shin rotates inward and with the shin, the thigh rotates inward. A so-called chain reaction. As mentioned above, the hamstring "wraps around" the lower leg. It attaches to the rear outer ends below the knee joint. Therefore it also has an influence here. It counteracts knee rotation and also internal hip rotation. In this sense, it is an external rotator.
In summary, the hamstring is an exconcentric and three-dimensional working muscle. Because it causes the load and the explosion by attaching to the pelvis and lower leg, it also has a great influence on movements of the foot and trunk.

The bottom line?

There is no device, nor will there ever be, that will fully account for the incredible function of this muscle! Train smart, Train functional with PAT!

Your Patrick

Article was originally published in Functional Training Magazine on 07/05/2014.

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