A group of researchers analyzed 16 weeks of training intensity data for 120,000 marathon runners who recorded their training ...

That’s often summed up (as in the title of Matt Fitzgerald’s 2014 book on the topic) as 80-20 running: around 80 percent of your running should be easy, with the other 20 percent medium or hard.

The Pareto principle, also known as the 80-20 rule, is a universal concept that has found application in various fields, from business and economics to health and personal development. At its core ...