Training your shoulders and chest muscles could be your most favoured sessions but are your shoulders preventing your chest muscles to expand properly. Did you know that too much training of your anterior deltoid (front shoulder muscle) can impose the chest muscles and make them look a lot smaller. Benching and shoulder pressing works the anterior deltoid muscle and overworking it could result in slouched shoulders. Make sure you are stretching this muscle and more importantly working your posterior deltoid (rear shoulder muscle) and back muscles so that it opens up your chest!!
If you feel you have a small chest yet work out hard and eat really well, it might be time to look in the mirror and stretch more. Turn side on in the mirror and ask yourself ''do my shoulders come forward?'' '' Do I need to work on my flexibility?'' When you are standing side on, retract your shoulders and notice the difference with your chest muscles. If you notice a difference then you now know what you need to do.