If God is to develop His plan in your life and you are to work at it with all your heart, then you must grow new spiritual muscle for the challenge. As a runner begins to train, his or her entire being is transformed. Within weeks of starting training the runner actually grows new capillaries. This extends the natural byways that allow blood to reach deep into muscle tissue so that oxygen saturates the recesses before hauling away waste products. Training works on a microscopic level; resulting in the increase of the number of cellular mitochondria. What is that? These are flash points where stored fuel becomes action. You might call them millions of spark plugs that are strategically located around your body and “fire” as you train.
Marty Jerome. Runner’s Day-by-Day Log and Calendar. Random House, New York, 2006, February-Fundaments.