About 15,000 men were initially surveyed about their level of weekly activity during a full health check between 1972 and 1973. In 2000, about 6000 surviving participants were retested and followed for up to 12 years. The results were recently published in the British Journal of Sports Medicine.
What was found was that 30 minutes of physical activity, irrespective of whether the activity was light or vigorous, six days per week, was associated with about a 40% reduction in mortality. Performing light activity for less than one hour per week had no survival benefit.