This is your longest run before your 26.2 mile race. It is long enough to acquaint you with the physical, mental, and emotional exhaustion you will face. When you head out for 23 miles feeling energetic, force yourself to stay below the maximum pace you can sustain. Feel free to stop and stretch. If you go too fast too early, you will deplete electrolytes, build up lactic acid, and raise your heart rate too high.