These two principles are crucial to developing and achieving length, strength & stretch in our bodies. The more resistance we create with our muscles pulling in different directions, the more stretch we will gain and the more challenged our muscles become.
Think about when we do a Full Roll Up; we are creating resistance and opposition. We are drawing our waistline back as we stretch forward towards our toes. We are not collapsing our torso towards our legs, but rather creating the two-way stretch and creating maximum stretch in our spinal muscles.
Next time you do your Full Roll Up, imagine you are doing a seated CAT stretch with lengthened legs (your " C " curve). Round over that imaginary beach ball in your lap, and create the oppositional pull. Keep your shoulder blades plugged down your back, and reach for those toes!