In his review of Play as if Your Life Depends on It, by Frank Forencich, Clarence Bass writes:
This hard-easy activity pattern is built into our genes. “[It] must have been repeated with variation millions of times throughout our history,” Forencich writes. It’s what we’re born to do. And it’s a proven formula for athletic success.
“An essential part of being a good animal is establishing a cycle of activity and rest that is appropriate for your species, your age and the conditions you live in,” Forencich writes. “From a coach’s point of view, the Paleolithic hunters and gatherers were following an ideal pattern for athletic excellence as well as general health.” When you train, train hard—and then take a few days off for rest and recovery.
As the fittest 70 year-old on the planet, Clarence's recommendations are worthy of attention by anyone interested in living long and well.