Tapping into different muscle groups and cardio systems is the best way to not only get in the best shape that you can be but to also keep things from getting too boring. This is why any athlete in training won't be doing the same old routine each and every day. Not only is it monotonous but after a while you're body will actually adapt to the workout program and not only won't improve but will actually find ways to cheat and use less energy. You don't want to get stuck in a rut, and I admit it is easy to fall into a comfortable routine and just zone out. But if you do this you're not going to do yourself any favors and instead you want to keep spicing things ups.

The two fitness systems are the anaerobic and aerobic capacities. Your anaerobic system is the one that you use for short bursts of maximum efforts; think sprints and plyometric jumps. You will only be using the fast twitch muscle fibers and the longest amount of time this system works alone before switching over to aerobic is about 20 seconds. The aerobic system then is what you use for sustained cardio exercise and works off of slow twitch muscle fibers; you can use this one much longer than the other. Both need to be addressed for a well rounded fitness training program but different people have different bodily make ups and varying ratios of slow twitch to fast twitch muscle fibers. That's why some people are more apt to be sprinters and high jumpers and other are marathoners.

Yet to get the most from your workouts you should try to mix in different exercises and types of training to hit these different capacities each week. For instance one workout should be geared toward faster, shorter sessions such as intervals of 30 seconds all out and then nearly full rest until the next one. You could also do plyometrics to tap into your fast twitch muscles. Then a second workout that week could be intervals of longer time or distance such as 3 minutes hard and then enough rest so that you can do the next one but not so much so that you are fully recovered. This will build endurance and stamina. You could also do a longer tempo effort which is at threshold level, just under a race effort, for 20 minutes or more.

A complete training program is going to stress all of your systems and maximize as many muscles as you can. This will not only keep you a well rounded athlete and improve your overall fitness and abilities but it will keep things fun and exciting as well.