Too many miles can lead to injury. Too few can result in disappointing progress. What's the answer? For many runners, it's cross training. Cross training is simply exercise that ISN'T the primary activity. If you're primarily a runner, cross training can include bicycling, elliptical machines, swimming, weight training, etc. The type of cross training you should utilize depends on your cross training goals. If you want to work on your cardiovascular system without straining your already-weakened leg muscles, swimming would be an excellent choice. However, if your goal is to work your cardio as well as your legs without suffering the pouding impact of outdoor or treadmill running, the elliptical machine or bike (including stationary bike) make great choices.
It is important to understand, however, that NO form of cross training will REPLACE the primary activity. The elliptical machine, for example, provides a workout that is very similar to running but if you were to train solely on the elliptical machine, you would be very poorly prepared for a road race. It simply isn't running. To run well, you need to run. Use cross training as a tool
and it will serve you well.NewbieWiki