Running is one of the most effective cardio activities around; per minute of exertion you will be able to stress your cardiovascular system the most, engage nearly every muscle in your body, burn the most calories, and elevate your heart rate the quickest. Whew, that's a pretty powerful fitness punch; but on the flip side running is a high impact activity and like I've said a thousand times before it does take a toll on the joints, tendons, ligaments, etc.

So while running may seem like the best cardio exercise there is, and I'd toast to that, the amount of running a person can do will vary. Some are just predisposed to winding up hurt and injured more than others; this has to do with bone structure, their running gait, and many other factors mostly out of their control. For this reason everyone has a certain running threshold that may only be 30 miles a week while those lucky others can train upwards of 100 miles a week and stay nearly injury free. Yet in training there are still ways to supplement your running regime that can improve your fitness level and translate to faster race times and an increased level of fitness and that is with cross training.

Cross training is really anything outside of your primary sport; for a swimmer cross training may actually be running! But for runners some of the most common forms of cross training are doing the elliptical machine, aqua-jogging, and some prefer the bike. The benefits of doing this is that it eliminates the high amount of stressful impact from running while still tapping into the cardiovascular system. Cross training may be done in addition to daily workouts and some may even put it in place of their easy days if they have a particularly low running threshold.

So while you will be able to get your heart rate up your joints will be taking less of a beating and because both aqua-jogging and the elliptical are very similar motions to running they are usually the two top picks. So if you are looking to give your running routine a little boost you may want to think about adding minutes of cross training instead of just piling on more miles. A general rule for increasing miles is to only add in 10% more weekly total volume at a time but you can add in nearly as much cross training as you want without such an increased risk for injury.

Finally, another powerful use for cross training is if you are injured and unable to run. Generally you can find SOMETHING that won't aggravate your particular injury and by keeping in relatively good cardio shape you will be able to bounce back faster when you are at last able to run again.