Levchin uses a cycling computer and a power meter. His performance data is displayed in real time, including speed, distance, heart rate, pedal cadence, and power. There's a GPS feature that maps his route, too. But he has to be careful, because all the data can lead to over-training. "My No. 1 enemy is the power meter," he says. "If the number has not cracked 300 [watts], I am not OK with that."