I love quads, they are my favorite cause there is 3 different spots to hit on the quads. high med low.
there is no special area to pin its wide open. if you take your hand and place it horizontally above your knee, with one side touching your knee, always pin above there. then take your hand and place it horizontally on your thigh at your groin. always pin below there. while sitting in a chair, legs at 90 degree bend at your knee-draw a line from the center of your knee all the way up to your groin, always pin outside that line. other than that it is wide open.
i flex my quad and wherever i see muscle i pin, i even pin straight down sometimes high on the quad, instead of outside.
the trick to them not hurting is making sure they are COMPLETELY relaxed when you pin them.
to do this I
1# sit on the floor, both legs extended and flat
2# place a small pillow under the bend in your knee
3# slap the quad hard where you will pin to get it numb
4# use off-hand to grab muscle about 4 inches wide and pinch
5# insert needle into pinched muscle
6# slowly let go off muscle with off-hand once needle is inserted
7# complete procedure
if i have a bad one i usually know right away. to avoid this insert needle slowly, and if you feel like you hit a nerve, pill back a lil and take slightly different angle. if it hurts going in its going to hurt later. try to avoid this
once you get the hang of it i rarely, rarely do i get a bad pin. i pin up to 3cc's in quads
high and inside is the least painful for me