A huge collection of research by other scholars backs Ericsson’s conclusions. A five-day workweek packed with extended working hours is, few experts dispute, suboptimal. A 2009 study published in the American Journal of Epidemiology found that those who worked 55 hours a week performed more poorly on some mental tasks than those who worked just 40 hours. A Harvard Business Review article touted the idea that, like middle-distance runners, people work best in 90-minute bursts, followed by periods of recovery. This allows our work schedule to synch with our bodies’ ultradian rhythms, the 90- to 120-minute cycles during which our bodies slowly move from a high-energy state of alertness into a physiological trough.