We’ve all heard this type of story before: Estonian karate master transforms from national-class martial artist to out-of-shape karate instructor to fast-improving distance runner.

Wait a second—we’ve never heard a story like this before! But it is the true story of Karl Viiol, a 35-year-old business consultant who lives in Tartu, Estonia, with his partner of nine years and their two children. Karl’s transformation began in 2018, when he bombed a VO2max test, an experienced that motivated him to buy a bike and ride with a group of out-of-shape middle-age dads, who left him in their dust. Stung by the double embarrassment, Karl decided to go all-in on endurance, training for and completing a 250-km Gran Fondo and then switching to half marathons.

Ever the competitor, Karl asked the winner of a local marathon to create his second half-marathon training plan, after completing the first in just under 2 hours. “It was too hard and my calves and Achilles got injured and I couldn’t run for two months,” he says. Having learned his lesson, Karl went searching for a more balanced way of training, and discovered 80/20. The result was a 20-minute improvement in his half-marathon time (“a massive success!”).

Karl’s advice for other Estonian karate masters (and everyone else) seeking to transform themselves into an endurance athlete through 80/20 plans is “to keep consistency, eat healthy, and remember to have fun with your training sessions.”