Rectus Femoris accelerates hip flexion how?

[kage65]

I'm trying to learn the muscles, and have a muscle animation program. Viewing it I can clearly see how the rectus femoris is responsible for knee extension. It is clear because I can clearly see the attachment of the muscle to the top of the patella.

What I can't understand is how it is also responsible for hip flexion. I don't see how it could do this if it only attaches to the patella.

Thanks for any help.

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[02143]

the origin of rectus is at the AIIS, which is on the pelvis, thus resulting in hip flexion

here's a picture from google that clearly shows the AIIS insertion: http://anatomy.askthetrainer.com/muscle-images/rectus-femoris-muscle.gif

 

[kage65]

Thank you 02143, but it looks like the muscle literally pulls on the patella, from the AIIS ( which is part of the pelvis ( I think ).

If it pulls on the patella, how can it lift the hip and the femur bone?

 

[02143]

Well, the femur is part of the "hip" joint that you are referring to. The flexion that you are asking about comes from the acetabulum/femur joint relationship. So, ignore the explicit patellar motion right now since you understand that. Lets just say that the knee is extended (for the sake of visualization). If the hip is in a neutral position, and the knee is extended, then the rectus is going to shorten between its origin and insertion and will result in "lifting" of the femur, which results in what we call hip flexion.

Does that help? I feel like my explanation isn't super great and someone else may be able to provide a clearer explanation.

 

[kage65]

It's a good explanation, thank you, but I'm still foggy. I guess I know how it works per say. Meaning I know the rectus contracts and shortens which results in the lifting of the femur.
If there was another bone that protruded out in front of the pelvis, say 8 inches, with another attachment point, and that was the origin of the rectus, then it would all be clear to me. Meaning it would be clear in my mind because then I would clearly see how the femur is lifted up by the muscle, because the origin point is well above the femur ( let's say 45 degrees higher). As it is it looks like the insertion point is on almost the same plane as the patella ( let's say maybe 5 degrees higher, if that.)
I'm envisioning this in my head this way. A puppets hand is lifted up by the puppeteer's hand from directly above , not from an angle in line with say, the shoulder of the puppet.
Now I'm not sure if my explanation is clear hehe.

 

[jesspt]

The rectus femoris crosses the hip joint anterior to the joint surfaces, making it a hip flexor (albeit a relatively weak one). If it crossed the hip posteriorly, it would be a hip extensor. A muscle will create a moment at every joint it crosses relative to where it crosses the joint (anterior, posterior, medially, or laterally).

A word of advice - don't think about this too much, particularly if you haven't had physics yet. Memorize the origin, insertion and action which should be enough to get you through a basic anatomy class, which I'm assuming is what you're taking given your status as a pre-health major.

 

[RUDPT6]

Hey my friend, let me offer a tip for your current studying dilemma. Grab a rubber band if you have it and place it on model skeleton's AIIS and the other end on the skeleton's patella. At this time, the rubber band will be lengthened or on tension. Keep your fingers on both bony landmarks (AIIS and Patella) while holding the rubber band. As the rubber band contracts or shortens, it will inevitability flex the hip.

 

[iamastudent]

The rectus femoris creates a moment, or a rotational force, at the hip. It does not pull it "straight up", you're right, it's almost in the same plane. It would jam the femur into the hip if it was like a string pulling straight up.