So whenever I do chest exercises I never feel them in my chest, and ony my shoulders. My gym teacher (I'm in a weight lifting class) looked at my back and said he thought my scaps were messed up, and that was causing the unusual shoulder activation. He said if I lie down, tense my core, and then breathe from my stomach it should help. He specifically said to do 20 reps a day. What are your thoughts on this?