I read a Frederic Delavier’s book « Strength Training Anatomy » and I learned good stuff.
Installed in the bench with your ankles blocked. The axis of the bending is done with the coxofemoral joint and the pubis is outside of the bench :
Your torso bent and you make an extension to the horizontal by raising your head
Then, you make a hyper extension (you accentuate the lumbar arch). Be careful, this hyper extension is to be done with caution to avoid injuries.
This exercise mainly works with all the spinal erectors muscles of the spine (iliocostalis lumborum, iliocostalis thoracis, longissimus thoracis, intertranversarii laterales lumborum), quadratus lumborum and a little bit the glutes and hamstrings (except the short head of the femoral biceps).
A complete flexion of the torso makes it possible to stretch the whole sacro-lumbar. By immobilizing the pelvis, what means that the axis of flexion is at the front of the body, effort is targeted on the sacro-lumbar muscles but less intensely because of the decrease in amplitude of the movement and increasing the power of the lever.
For even better muscle work, you can maintain alignement for a few seconds at the end of extension.
For beginners, there is a incline bench recommended for ease of movement execution.
There is a machine that specifically targets work on the sacro-lumbar of the spinal muscle (the machine I use).
To increase the intensity of the exercise, you can make the movement with a weight plate held behind your neck or tight against your torso.
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