The Push:Pull Ratio
Nearly every upper body exercise can be classified as either a pulling (or curling) exercise or a pushing exercise.
Pulling movements are where you embrace the environment and bring it into the body. Chin ups, rows, bicep curls, these exercises work scapular retraction and humeral extension. The main drivers here are the lats, traps, and rhomboids, with the bicep flexing the elbow along the way.
Pushing exercises are the exact opposite and are all about protraction (in some cases), humeral flexion and elbow extension. Pecs, deltoids, serratus anterior, and triceps are going to be the main muscles worked here.
Everyone loves training push exercises because they make you feel like a bad ass. With exercises like the bench press, as we press we move into a position of biomechanical advantage and our sarcomeres (the part of the muscle with the actin and myosin filaments) reach their position of optimal overlap, making the movement easier as we press. Pressing exercises are also done in front of our eyes so we can see the weight moving, which adds to the badassery
With pulling exercises, all the things about pressing that makes it fun are stripped away. As you pull and the scapula close in together our muscles and joints move into a position of biomechanical disadvantage.
The problem with the love and enthusiasm for our pushing work is we're tightening up and strengthening our numbers one and two internal rotators and protraction muscles, pec major and pec minor.
So if you spend any amount of time in the car, at a desk, on the couch, or playing Pokémon Go, you should be balancing out every set of bench press, push-ups, inclined bench, pec flys, overhead press, with twice as many sets of inverted rows, pull-ups, cable rows, external rotations, chin-ups, Y's, T's, W's, reverse flys, and pec stretches.
But not upright rows. Don't ever do upright rows. They're bad for your shoulders.