Fueling physical activity and fatigue Module 3- Metabolism and Nutrition

Energy Production and Capacity All energy systems are contributing at all times In general, there is an inverse relationship between a given energy system’s maximum rate of ATP production (i.e., ATP produced per unit of time) and the total amount of ATP it is capable of producing over a long period As a result, the phosphagen energy system primarily supplies ATP for high-intensity activities of short duration, the glycolytic system for moderate- to high- intensity activities of short to medium duration, and the oxidative system for low-intensity activities of long duration

Rate the oxidation of fats and proteins, phosphagen system, aerobic glycolysis, oxidation of carbodydrate and anaerobic glycolysis is terms of rate and capacity of ATP production ATP Production Rate Phosphagen Anaerobic Glycolysis Aerobic Glycolysis Oxidation of Carbohydrates Oxidation of Fats and Proteins ATP Production Capacity Oxidation of Fats and Proteins Oxidation of Carbodydrates Aerobic Glycolysis Anaerobic Glycolysis Phosphagen

Key Point The extent to which each of the three energy systems contributes to ATP production depends primarily on the intensity of muscular activity and secondarily on the duration. At no time, during either exercise or rest, does any single energy system provide the complete supply of energy

Lactate Threshold and Onset of Blood Lactate Accumulation Lactate Threshold (LT) Represents an increasing reliance on anaerobic mechanisms LT is often used as a marker of the anaerobic threshold Occurs because of increased rate of glycolysis, decreased lactate removal rate and insufficient oxygen Occurs at 50-60% of VO2 max for untrained individuals and 70-80% for trained individuals Onset of Blood Lactate Accumulation (OBLA) Occurs when the concentration of blood lactate reaches 4 mmol/L (rest less than 1 mmol/L)

Lactate Threshold and Onset of Blood Lactate Accumulation These two breaks are thought to represent the points at which intermediate and large motor units are recruited Training at intensities near or above the LT or OBLA pushes these points “to the right” This shift probably occurs as a result of changes in hormone release and increased mitochondrial content This shift allows athletes to perform more work before fatigue sets in

Oxygen Uptake and the Aerobic and Anaerobic Contributions to Exercise Oxygen uptake (consumption) is a measure of a person’s ability to take in and use oxygen Then what is VO2 Max A person’s maximum ability to take in and use oxygen Oxygen deficit is the anaerobic contribution to the total energy cost of exercise This occurs because of the time it takes for the aerobic energy systems to “kick in” (Remember to relative rates of ATP production) Oxygen debt (excess postexercise oxygen consumption [EPOC]) occurs when the oxygen uptake value is still elevated post-exercise in order to restore the body to return to its pre-exercise state

75% of V02 Max

80% of Maximum Power Output (Anaerobic Exercise)

Oxygen Deficit Due to lack of oxygen early in exercise, anaerobic pathways are needed to produce ATP Pyruvate and hydrogen from NADH converted to lactate and hydrogen because there was not enough oxygen in the mitochondria These hydrogen ions Interfere with calcium binding to troponin Reduce calcium release from sarcoplasmic reticulum Decrease the ph, causing phosphofructokinase to slow down glycolysis Chemical receptors in the cell detect hydrogen (burning sensation), affects the CNS and can eventually cause inhibition of motor unit recruitment by the motor cortex

EPOC Possible factors increasing excess post-exercise oxygen consumption: Resynthesis of ATP and creatine phosphate stores Resynthesis of glycogen from lactate Oxygen resaturation of tissue water, venous blood, skeletal muscle blood and myoglobin Redistribution of ions within various body compartments Repair of damaged tissue Additional cardiorespiratory work Residual effects of hormone release and hormone accumulation Increased body temperature

Substrate Depletion and Repletion Phosphagens Creatine phosphate can decrease markedly (50-70%) during the first stage (5-30 seconds) of high- intensity exercise and can be almost eliminated as a result of very intense exercise to exhaustion. Postexercise phosphagen repletion can occur in a relatively short period; complete resynthesis of ATP appears to occur within 3 to 5 minutes, and complete creatine phosphate resynthesis can occur within 8 minutes Half life of creatine phosphate replenshment is 30 seconds 50% recovered in 30 seconds, 75% in 60 seconds, 87.5% in 90 seconds, etc.

Substrate Depletion and Repletion Glycogen The rate of glycogen depletion is related to exercise intensity. At relative intensities of exercise above 60% of maximal oxygen uptake, muscle glycogen becomes an increasingly important energy substrate; the entire glycogen content of some muscle cells can become depleted during exercise Repletion of muscle glycogen during recovery is related to postexercise carbohydrate ingestion. Repletion appears to be optimal if 0.7 to 3.0 g of carbohydrate per kg of body weight is ingested every 2 hours following exercise