How to train lower chest on pec deck chest fly machine? Pec deck fly machine is commonly used in the gym to train the middle chest (sternal part of pec major). With little adjustment, it can be used to train the lower chest too. Slightly move the butt at the front of the seat, to slant the torso so that the lower chest muscle alignment is aligned with the machine resistance. Notes: I still prefer high to low cable fly for lower chest. This offers alternative when the gym has limited equipment, o