80/20 Endurance is the creation of Matt Fitzgerald and David Warden. Based on the breakthrough books 80/20 Running and 80/20 Triathlon, runners, triathletes, and other endurance athletes improve the most when they consistently do 80 percent of their training at low intensity and the other 20 percent high intensity. The typical endurance athlete spends only 50-70 percent their total training time at low intensity. The solution? An 80/20 training plan that ensures the optimal intensity balance.