I have heard that the chest muscles are the last to mature in the body.From the age of 14 when I first started training until I was 19, I pounded my chest every week with benches and flyes and my chest didn't grow one bit.Eventually it began to develop, even though it lagged way behind the rest of my body(with the exception of my calves).Now, just working my chest once every two weeks or so I notice significant progress.My best "routine" for chest is 3 sets of dumbell benches performed on a swiss ball and pausing in the bottom position for a count of two seconds.The ball calls into play all the muscles of the torso to assist in the movement and it allows an awesome stretch in the chest muscles.Another exercise I have found beneficial in building up the chest that also emphasizes a good stretch is weighted dips on the parallel bars.Maybe stretching exercises are more beneficial in building up the chest rather than simple pressing exercises?
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