What is the greatest resistance to person using the core and their breathing ability is stress in shoulders and tension in the body muscles. The greater the stress in shoulders the less connection person has to their core muscles ability to move them to affect breathing which affects person emotional connection to the body. There is direct relationship between core movement and shoulders being tight from emotional thoughts that form stress. The more person engages core muscles to start and end their inhalation and exhalation the less stress in shoulders can exist which lets person feel their strength. When the core/breathing is not done your strength is gone and when person starts to breath totally out the mouth you have lost their strength physically and emotionally weaker to direct muscle action. Lowering your shoulder stress before you even start your work out will let person become emotionally and physically engage in the work out faster with more fat burning time during the work out and boredom will not be part of the workout. Boredom is the mental disengagement of what you are doing at the gym physically.