In a break with training orthodoxy, Potts and his coach have created a regimen called feedback training in which the training plan is reassessed every 24 hours based on the constant monitoring of three variables: wattage (the power Potts’s body produces), cadence (the tempo of his arm and leg movements) and heart rate. No lap times. No mileage. No grand training schedules planned months in advance. Only raw biological data. “My coach and I talk a lot about engines,” Potts says. “In auto racing, you want to put out the highest amount of power with the least amount of fuel. We do the same thing. My heart and lungs are my engine. The goal is to always increase the efficiency of the engine.”

Every night, Doane analyzes his athlete’s response to the day’s training. He’s looking for the best way to expand Potts’s aerobic capacity, power output and lactate threshold, without overtraining. If Doane sees that Potts’s heartbeat has been sluggish—say, beating 140 times per minute while Potts is trying to produce 410 watts—that means his body is struggling to recover from earlier training, so he’ll dial back the intensity of his workouts. If, on the other hand, his heart rate stays in the sweet spot around 165 while he churns through a series of 360- to 400-watt intervals, that means he’s fully recovered and ready to be pushed again. “We’ve created a feedback loop,” Doane says. In other words, Doane subjects Potts to a careful dose of punishment, and Potts’s body tells Doane, through empirical data, what he needs to do next.