Squat Report: The Hip Part II (Extension)
Last week we took a look at the hip and what happens during flexion, we saw that when the hip flexes it naturally wants to internally rotate and adduct (legs want to come together).
This week we are going to look at the opposite. Extension. And, naturally, the hip at this stage will want to externally rotate and abduct (move away from each other).
On a structural level the bone doesn’t change, however, the movement of the head of the femur in the socket of the pelvis does. During extension of the hip the head of the femur will rotate upward and outward almost causing the femur to “pop” out of the ball and socket joint that it creates.
On a muscular level many different things come into play as the forces here are so great the muscles are some of the most powerful that we have at our disposal.
All these muscles are extremely powerful muscles (i.e. the gluteus maximus has a pulling capacity of 249 kg. [Kapanji, The Physiology of the Joints, Lower Extremity]) but they also have other functions as well.
The Gluteus Medius is also helps flex and internally rotate the hip, externally rotate the hip (anterior fibers and posterior fiber, respectively), and when they work together they can adduct the hip.
The Gluteus Maximus is also an adductor and external rotator, and the upper fibers act as abductors of the hip.
The adductor magnus also flexes the hip, and can externally rotate the hip when flexed (this was covered last week)
Biceps Femoris is also a knee flexor and when the knee is slightly bent, it can rotate the leg outward
Semitendinosus is also a knee flexor and can medially rotate the tibia
Semimembranosus is also a knee flexor and can also medially rotate the tibia
There are a few more muscles that are not mentioned here that are more apart of the hip gridle only because these are very deep muscles that have a role in more than just hip flexion and extension. We will get into these next month when the Squat Report continues.
One more point to take into consideration is that when we perform a squat and we are getting out of hip extension the external oblique must be engaged to provide stability to the pelvis as an anchor would a boat. This would happen on the lower fibers of the external oblique, but we will get into that in a few more months.