In an interview with The Globe and Mail, Tony Schwartz, author of the NY Times bestseller The Way We’re Working Isn’t Working, says we should be working no more than 90 minutes.

Schwartz says

“there is a rhythm in our bodies that operates in 90-minute intervals. That rhythm is the ultradian rhythm, which moves between high arousal and fatigue. If you’re working over a period of 90 minutes, there are all kinds of indicators in your physiology of fatigue so what your body is really saying to you is “Give me a break. Refuel me.”

Do you take regular intervals? What’s your limit?