80/20 Running: Run Stronger and Race Faster by Training Slower2014

"Respected running and fitness expert Matt Fitzgerald explains how the 80/20 running program--in which you do 80 percent of runs at a lower intensity and just 20 percent at a higher intensity--is the best change runners of all abilities can make to improve their performance. With a thorough examination of the science and research behind this training method, 80/20 Running is a hands-on guide for runners of all levels with training programs for 5K, 10K, half-marathon, and marathon distances"--