The glycolytic energy system (also called glycolysis) involves the partial break down of glucose to a molecule called pyruvate. During this process, a relatively small amount of energy is produced. When oxygen demands exceed oxygen supply, pyruvate is converted to lactate. Under these circumstances, glycolysis is often referred to as “fast” or “anaerobic” glycolysis. Anaerobic glycolysis is a key contributor to total energy requirements for moderate to high intensity exercise lasting about one to two minutes, such as a round or sparring. Although this system can provide a rapid source of energy, it is only about half as fast as the phosphagen system. When there is enough oxygen to meet oxygen demands of an activity, such as during prolonged light to moderate intensity hand target drills, glycolysis proceeds much slower and the pyruvate that is formed participates in formation of additional energy via aerobic processes (see Aerobic System discussion below). In this case, glycolysis is sometimes referred to as “aerobic” or “slow” glycolysis.
Mitochondrial respiration refers to aerobic processes that occur when there is sufficient oxygen to meet oxygen demands of activity. The aerobic energy system comes into play during any exercise lasting longer than one minute, and as duration of exercise goes beyond several minutes, aerobic energy production becomes increasingly more important. Aerobic energy production is much slower than both the phosphagen and anaerobic glycolytic energy systems, but it has benefit of being able to provide almost unlimited energy, as long as nutrients are available. Examples of activities that rely primarily on aerobic energy production include a 10,000-meter run, cross-country skiing, and a 1,000-meter swim.
We often think of low to moderate intensity aerobic exercise as a good way to burn a significant amount of fat. While this is true, aerobic energy can be derived from carbohydrates and to a much smaller extent, protein. In fact, most people do not realize that even during light to moderate exercise, carbohydrates can provide up to 40 to 60 percent of total energy requirements. In contrast, protein is not a preferred source of energy during any form of exercise (assuming an adequate diet) and generally contributes less than 10 percent of total energy requirements.