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.
“I'm useless at staring at a piece of white paper. But if you put a piece of white paper with a black line on it in front of me, I'll say no that black line should be red and it should go this way or that way.”
“In Mexico an air conditioner is called a politician because it makes a lot of noise but doesn't work very well.”