Fueling Aerobic and Anaerobic Activities
Aerobic and anaerobic activities are fueled through different physiological energy systems. Aerobic activities such as low to moderate-intensity walking, jogging, swimming, cycling or hiking require a continual supply of oxygen. From a fuel standpoint, protein and fat require oxygen for combustion, while carbohydrate can be burned with or in the absence of oxygen. In the case of physical activity that is aerobic in nature, approximately 40% of the energy expended in a 60-minute walk is derived from carbohydrate, 55% from fat and 3-5% from protein. The low to moderate pace of aerobic activity allows the cardiovascular system to gradually adapt to the increased oxygen demands of working muscles, which allows more fat to be used as a fuel source (1).
In contrast, anaerobic activities burn energy rapidly for short durations without oxygen. Rapid anaerobic energy transfer maintains a high standard of performance for maximal short-term efforts such as sprinting in a pool, stopping and starting over and over again on a basketball or tennis court, or doing repetitive movements in weight lifting. Anaerobic movements rely on three fuel sources that do not require oxygen to be burned: adenosine triphosphate (ATP), creatine phosphate (PCr) and carbohydrate in the form of glycogen (1). Compared with fat and protein catabolism, carbohydrate remains the preferential fuel during high-intensity anaerobic exercise because it rapidly supplies ATP during oxidative processes. High-intensity anaerobic exercise uses approximately 70% glycogen, 15% fat and 5-8% protein (1).
Regardless of the type of physical activity undertaken, energy is burned. The number of kilocalories burned with exercise depends on a number of factors, including: the duration of the activity (e.g., 30 minutes vs. 60 minutes), the frequency of the activity (e.g., once per week vs. five times per week), the intensity of the activity (e.g., walking 4 kilometres per hour vs. 6 kilometres per hour) and an individual’s weight (1, 3, 6).