Sri Chinmoy: While you are running — especially when you are tired — you are much more conscious of your breathing. You are more aware of when you are inhaling and when you are exhaling. While running, when you inhale, you can consciously invoke divine energy to energise you. This divine energy energises the willing reality in you and illumines the unlit reality in you so that you can become a perfect instrument of God. When you breathe in the divine energy, automatically it changes or transforms undivine forces into divine forces.
Each time you breathe in, if you can repeat just one time God's Name, or 'Supreme', or whatever divine name or form comes to mind, then that spiritual thought will increase your purity. Either it turns into purity within you or it grants purity to you. Then, when you breathe out, feel that a new eagerness and a new promise are going out from you to the Universal Consciousness. This new promise is nothing short of your sincere willingness and eagerness to become a good and perfect instrument of the Supreme.