Younger employees often put in long hours, cutting back on sleep to get ahead, and chief executives usually lead the charge with a ferocious attitude to red-eyed invincibility.

But BHP chief executive Andrew Mackenzie said less was more when it came to productive hours at work.

"I've found that the more senior I've become, the more important it is that I work fewer hours," Mr Mackenzie said. "A rested Andrew can do more in four hours than a tired Andrew can do in eight.

"It's not only diminishing returns, [not being rested] is like a scorpion's tail; it can undo things," he told Qantas magazine.