When you’re hurt and have to cross-train, try to spend more time on it than you do your running. After all, you can get in a decent run in 30 minutes, but you’re not going to find lots of cyclists who would consider half an hour anything but a warm-up. Make the time go faster on individual workouts by translating your usual hard running workouts—VO2 max sessions, tempo workouts, etc.—to the pool or bike or elliptical or wherever you’re spending your non-running time. Structure crosstraining weeks like your running weeks; the variety will help your time in injury limbo pass faster than if you do the same medium-effort waitingout-the-clock effort every day.