Cross-Training Time

You wouldn’t expect to feel comfortable running if you did it only once a week, but that’s the approach that many runners take to their alternative exercises. This approach isn’t a good idea, because you’ll never become adept enough at the activity for it to contribute significantly toward your fitness. So when you find a second sport that works for you, try to practice it at least twice a week.
Unless you’re injured and are cross-training as a substitute for running, don’t let your aerobic alternatives take precedence over your running. For example, you don’t want to put in such a long, hard effort on a bike that your running is compromised for the next few days. Once you get used to your activity, treat it the same as an easy running day. You shouldn’t be sore or overly fatigued from your cross-training. One of the best times to schedule cross-training into your routine is on the day after a hard or long run. The exercise will help to remove waste products that might have built up from the previous day’s effort and will help work out any stiffness, but you won’t be subjecting tired legs to as much pounding as if you ran.