Why do it: I get a lot more milk faster and it’s also more fatty. Compression increases hindmilk by 20% or so I read. Massaging/compression can aid in more letdowns. Babies use compression and suction, so you are simulating that. Pumps just suck. (Pun only sort of intended.)
Science on this.
How I do it: I knead and press my breasts, particularly the upper part by armpits. Different things work for different people but that upper outer quadrant is really effective for lots. Be careful not to damage breast tissue. My LC says that just keeping a fist up near your armpit on your breast is what works for a lot of women. You want to help move the milk towards the nipple, so without dragging your skin, you might want to massage down.
Pumping tips from Dr.Sears that talks about pumping and massage.
