Aerobic soccer fitness determines the level at which you can take in and use oxygen to perform an activity. An activity like walking doesn't put much stress on your body and most people can cope with this aerobic activity. Aerobic activities are activities like jogging, where you can continue without getting too tired. You work at a rate which means you don't get completely fatigued or out of breath. Aerobic training will decrease the level at which this fatigue takes place, and will make your heart and lungs more efficient for exercise.