Optimizing Human Performance

Energy Systems

AA 2There are three basic energy systems used to replenish ATP: Phosphagen System, Glycolysis, Oxidative System Lets first clarify what Anaerobic and Aerobic mean. Anaerobic refers to processes that do not require the presence of oxygen, whereas aerobic mechanisms depend on oxygen. Of the three macronutrients, only carbohydrates can be metabolized for energy without the direct involvement of oxygen. All three energy systems are active at any given time; however, the magnitude of each system to overall work performance is primarily dependent on the intensity of the activity and secondarily on the duration. Phosphagen System Provides ATP primarily for short-term, high-intensity activities (e.g., power clean and sprinting) and is active at the start of all exercise regardless of intensity. The phosphagen system cannot be the primary supplier of energy for continuous, long duration activities because creatine phosphate (CP) is stored in relatively small amounts. Type II (fast-twitch) muscle fibers contain higher concentrations of CP than Type I (slow-twitch) fibers; thus, individuals with higher percentages of Type II fibers may be able to replenish ATP faster through the phosphagen system during anaerobic, explosive exercise. A good test to see how proficient you are at replenishing ATP is to do a CP Battery Test: Build to a 1RM Power Clean, Rest 8 minutes, Then an 8 minute AMRAP of Power Cleans at 90%. Top scores are 35+. AA 3 Glycolysis Glycolysis is the breakdown of carbohydrates, either glycogen stored in the muscle or glucose delivered in the blood, to resynthesize ATP. The ATP resynthesis rate during glycolysis is not as rapid as with the phosphagen system but the capacity is much higher due to a larger supply of glycogen and glucose compared to CP. Pyruvate, which is the end result of glycolysis, can be converted to lactate or shuttled into the mitochondria. I won’t get into too much detail here; just recognize there is an anaerobic (fast) glycolysis and an aerobic (slow) glycolysis. Essentially the fate of pyruvate is controlled by the energy demands within the cell. Lactic acid is a naturally occurring organic compound produced in everyone’s body and is both a by-product of and a fuel for exercise. It is found in the muscular system, the blood, and various organs. It is a by-product of activity at certain time domains and relative intensities. Training and progression dictate the favorable or unfavorable use of lactic acid. Although the muscular fatigue experienced during exercise often correlates with high tissue concentrations of lactate, lactate is not the cause of fatigue. Most people view the formation of lactate as a negative event when it is often used as an energy substrate, especially in Type I and cardiac muscle fibers. An exercise-induced decrease is pH is referred to as metabolic acidosis and may be responsible for much of the peripheral fatigue that occurs during exercise. Recent evidence suggests that other mechanisms, such as the simple hydrolysis of ATP, are responsible for most of the H+ (a hydrogen proton) accumulation and that lactate itself actually works to decrease metabolic acidosis rather than accelerate it. Along with exercise intensity and muscle fiber type, exercise duration, state of training, and initial glycogen levels can also influence lactate accumulation. The clearance of lactate from the blood reflects a return to homeostasis and thus a person’s ability to recover. Blood lactate concentrations normally return to preexercise values within an hour after activity. Light activity postexercise has been shown to increase lactate clearance rates. Peak blood lactate concentrations occur approximately 5 minutes after the cessation of exercise and is greater following high-intensity, intermittent exercise, think Fran or more recently 15.5. Lactate threshold (LT) is the maximum effort that can be sustained for an extended period of time without lactate steadily accumulating, this typically begins at 50-60% of maximum oxygen uptake in untrained individuals and at 70-80% in trained athletes. The ability of an athlete to withstand the intense pain that is produced by high acid levels is referred to as lactate tolerance, which is primarily more mental than physical. Training at intensities near or above LT in turn delays the accumulation of lactate to occur at a higher intensity which allows the athlete to perform at higher percentages of maximal oxygen uptake without as much lactate accumulation in the blood. Try this Lactate Buffering exercise: 30 sec on Assault Bike/Air Dyne @95%, walk rest 2:30 min x 4 + 7-10 minute break + 30 sec on Assault Bike/Air Dyne @95%, walk rest 2:30 x 4. Oxidative (Aerobic) System The oxidative system is the primary source of ATP at rest and during low-intensity activities and uses primarily carbohydrates and fats as substrates. During high-intensity aerobic exercise, almost 100% of the energy is from carbohydrates, whereas during prolonged, submaximal, steady-state work, there is a gradual shift from carbohydrates back to fats and protein as energy substrates. Aerobic capacity is the maximum amount of energy that can be produced by the aerobic system during physical activity. Aerobic capacity is directly related to anaerobic capacity, as a higher aerobic capacity allows the athlete to better buffer lactate, sustain more intense based training, and recovery from intense training sessions more rapidly. An example of an exercise for this system would be a 30 min Row/Run/Assault Bike/Air Dyne/Ski-Erg. AA 1 Recap The primary source of energy is dependent on the intensity and duration of the events. In general, short, high-intensity activities rely on the phosphagen energy system and fast glycolysis. As the intensity decreases and the duration increases, the emphasis gradually shifts to slow glycolysis and the oxidative energy system. At no time, during either exercise or rest, does any single energy system provide the complete supply of energy. During exercise, the degree to which anaerobic and oxidative systems contribute to the energy being produced is determined primarily by the exercise intensity and secondarily by exercise duration. Duration of Event Intensity of Event Primary Energy System(s) 0-6s Extremely High Phosphagen 6-30s Very High Phosphagen and fast glycolysis 30s-2min High Fast glycolysis 2-3min Moderate Fast glycolysis and oxidative >3min Low Oxidative


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