If you want running at 5:00-mile pace to feel easier, you should head out the door and run at 5:00-mile pace—a lot. Over time, your heart will get stronger, your muscles will grow more energy-producing mitochondria, and you’ll sprout new capillaries to distribute oxygen-rich blood. These changes will allow you to sustain 5:00 pace with less physiological strain, and they’ll also attenuate the distress signals that your muscles and heart send back to the brain. The pace will feel easier, so you’ll be able to sustain it for longer.
