|Quadriceps group: Vasti Lateralis, Intermedius, & Medialis plus Rectus Femoris.
Since the action of the quadriceps muscle group - the four major muscles on top of the thigh - is to straighten the knee and lift (flex) the leg in front of the body, how in heaven's name are we supposed to subvert nature and lift our legs?
Enter the next myth: "Lift from underneath." Another miraculous subversion of nature, whereby the hamstrings, the long muscles group behind the thigh whose action is to bend the knee and extend the leg behind the body, are now supposed to do what the quadriceps do - a kind of anatomical inversion.
(check out this blog: http://www.danceadvantage.net/leg-from-underneath/)
These well-meant and sincere corrections from excellent teachers confuse dancers. Let's be clear: you cannot dance classical ballet without using your quadriceps since the function of the quads is to straighten the knees and lift the legs. Nor can the hamstrings, which, in a front leg lift, must lengthen in order to permit the leg to go up - and those with tight hamstring know this because the tighter the back of your leg, the lower your leg will be when you try to lift it - serve as leg lifters.
I think teachers are trying to describe a subjective sensation: that a leg lift does not come from muscling or tensing the front of the legs, but from a feeling of release in the back of the legs. This release creates a feeling similar to a rush of wind under a skirt - a sensation of lifting from underneath. It might be more helpful to try to describe this than to perpetuate confusion and cognitive dissonance with inaccurate statements about the function of muscles.
|View of hamstrings, rotators, IT band from the back.