Anaerobic Exercise

Basically speaking, Anaerobic Exercise happens when there is not enough oxygen in your blood to process energy Aerobically so your body has to break down sugars to produce energy. The byproduct of this process is lactic acid which is responsible for the soreness you feel after some workouts.

Anaerobic training develops short, intense, powerful movement that lasts from a few seconds to around 2 minutes and takes place between @85% - 100% of your maximum heart rate. (See Target Heart Rate) Some of the more common workouts are heavy weight lifting, sprinting (running, biking, swimming), interval training and isometrics.

The most important benefits areincreased muscle size and strength, a stronger heart and lungs and increased stamina which helps you overcome exercise fatigue better during peak physical exertion.

It's not completely necessary but I highly recommend interval training and Plyometric as part of any well balanced workout routine.