Stop running your easy days too hard and your hard days too easy. Stepping up to the half-marathon requires safely expanding your aerobic engine without incurring injuries. Designed specifically for beginners taking on 13.1 miles, this 20-week plan uses the proven 80/20 Endurance methodology. You will run 4 days a week, keeping the vast majority of miles purely aerobic (Zone 2) to safely build time-on-feet. To elevate fitness, you'll dedicate just one day a week to high-quality speed work, ...