91 A Christian Guide to Body Stewardship, Diet and Exercise The purpose of this chapter is to introduce some of the key principles necessary in order to design and implement a safe and effective personalized endurance training program. However, before designing such a program, it is important to first understand the different biological energy systems used by the body to produce energy. Biological Energy Systems There are three basic energy systems used to replenish levels of adenosine triphosphate (ATP), the energy used to power muscle contractions: phosphagen, glycolytic and oxidative. The phosphagen system produces ATP primarily for an extremely short duration (≤ 10 seconds) and very high intensity activities such as heavy resistance training and short distance sprints (≤ 100 meters). The glycolytic system produces ATP for short duration (> 10 seconds - < 2 minutes) and high intensity activities such as high-rep resistance training and long-distance sprints (e.g., 200-m, 400-m, 800-m sprints). In contrast, the oxidative system produces ATP for long duration (> 2 minute) and low to moderate intensity activities such as walking, jogging and riding a bike. The phosphagen and glycolytic systems are anaerobic systems (not requiring the presence of oxygen) that occur in the sarcoplasm of muscle cells. The oxidative system is an aerobic system (requiring the presence of oxygen) that occurs in the mitochondria of muscle cells. All three macronutrients (i.e., carbohydrates, protein, fat) can be used to produce ATP, but only carbohydrates can be metabolized without the presence of oxygen. As a result, carbohydrate availability is crucial during anaerobic metabolism. Table 5.2 depicts the characteristics of the three biological energy systems (Haff & Triplett, 2016; Walters & Byl, 2013). Table 5.2. Characteristics of the Phosphagen, Glycolytic and Oxidative Energy Systems Phosphagen Glycolytic Oxidative Exercise Duration 0-10 sec. 11-120 sec. > 2 min. Exercise Intensity Very High High Low to Moderate Rate of ATP Production Immediate Rapid Slow Fuel ATP Muscle Glycogen / Blood Glucose Stored Carbohydrate and Fat Oxygen Used? No No Yes It is important to emphasize that all three energy systems are always active. The extent to which each system is active and contributing to ATP production is dependent upon exercise duration and intensity. Table 5.3 depicts the percent contribution of anaerobic and aerobic metabolism based on exercise duration (Haff & Triplett, 2016). Table 5.3. Percent Contributions of Anaerobic and Aerobic Metabolism 0-5 sec. 30 sec. 60 sec. 90 sec. 150 sec. 200 sec. Anaerobic 96 75 50 35 30 22 Aerobic 4 25 50 65 70 78
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