the sly motion stretches the peck, thus when it spumped u feel the pump to a different degree
its liek doing a bicep curl, and a preacher or concentration curl, when u curl u may feel the pump or a certain part of the muscle hti to a certain extent, but thats mearly the angle that creates this
the actuall targeting of a minor muscle is a rumour, trying to shape a muscle is impossible
if it were true we could shape a muscle, we might all be able to have bicep peaks like arni, and split chests, wide lats, and monstered calves
in end of day we cant shape and target different heads, even when trying to hit a different head u still hit the major muscle head since this is the main muscle used in the motion
blood pump has very little to do with muscle growth, again another bodybuilding myth, circulating blood through the body has very little role when muscle fibers are damaged n torn, theirs no evidence to support increased blood flow will increase muscle growth
u can even read a supplement companys NO products labels, which are meant to increase blood flow
all products will state 'blood flow CAN increase muscle growth', the word CAN shows theirs no proof
sorry but ye aur off base, if muscle pump determined growth wed all train in 20 rep ranges since the pump their is better then if we trained with 8 reps