It's a question of spreading the available energy, aerobic and anaerobic, evenly over four minutes. If you run one part too fast, you pay a price. If you run another part more slowly your overall time is slower.
“In the beginning the Universe was created. This has made a lot of people very angry and been widely regarded as a bad move.”
“If you believe that feeling bad or worrying long enough will change a past or future event, then you are residing on another planet with a different reality system.”