This system takes carbohydrate stored in muscle cell (glycogen) and breaks down glycogen to replenish ATP. Sports that utilize the glycolytic system include mid-distance sprinting, basketball, volleyball, boxing and football. These are all sports that involve long periods of moderate activity mixed with short periods of near maximum effort. Marathon runners and distance runners, use the aerobic system. The aerobic system uses oxygen to produce energy.

The blood carries oxygen, so this system has the greatest influence on the heart. Any activity that is prolonged (more than a few minutes) and does not involve repeated bouts of maximal effort, about the aerobic system used as the primary source of energy. Note that all systems are being used, but the aerobic system becomes the predominant system. The speed at which your heart is pumping can help indicate which energy system is dominant in any period of time. This is where the maximum heart rate and heart rate become useful purpose. Traditionally, training areas, "have been determined based on the percentage of target heart rate. The breakdown of these training areas is as follows: 50% – 60% = low intensity 60% – 70% = area of burning fat 70% – 80% = aerobic zone 80% – 90% = anaerobic zone 90 % – 100% = maximum area of low intensity zone is ideal for burning calories without stressing your body. If you are recovering from a workout or an injury, with a low calorie diet, or looking to burn additional calories with minimal impact on muscle gains, this a great zone to work out in.