Hal advises you to spend extra time stretching–and do some strength training too. Do this on “easy” days, and don’t overdo it. It’s wise to stretch every day, particularly after you finish your run. And don’t forget to stretch while warming up for your hard runs.
Hal can’t emphasize this strongly enough: Advanced runners need to spend more time stretching than novice or intermediate runners! That’s because you probably run faster and train harder, which can stiffen the body.
And don’t forget at least some strength training, which could consist of push-ups, pull-ups, use of free weights or working out with various machines at a health club. Runners generally benefit if they combine light weights with a high number of repetitions, rather than pumping very heavy iron.