Chapter 5: Training for Endurance 97 for a few, most endurance athletes would be better served by constructing their own training regimen based on a good working knowledge of the sound principles and an understanding of their own physical limitations and needs. (p. 490) 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
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