Energy and the Body

3. How do we get energy from ATP? The energy for all muscular contraction (and for all biological work like teeth growing etc.) comes from the breakdown of Adenosine Triphosphate into Adenosine Diphosphate (ADP). 3 phosphate molecules

4. The Energy Systems There are 3 energy systems for ATP re-synthesis within the muscle: The Immediate Energy System * At the onset of exercise, or during very brief, high-intensity exercise, a chemical compound called creatine phosphate (CP) breaks down in response to ATP’s breakdown. It quickly releases energy that reforms ATP. CP is the first fuel reserve called upon to restore ATP. *All CP stores are depleted within approx. 10 seconds of maximum activity/effort. The body needs up to 5 minutes of rest for those stores to be rebuilt. For each molecule of CP that breaks down, 1 of ATP is re- synthesised.

6. The Lactic Acid Energy System * For activities that are performed at near maximum intensity for approx. 20 seconds to 3 mins, a different fuel source is used. This fuel comes in the form of muscle glycogen. *Glycogen is a complex form of stored sugar obtained from carbohydrates (CHOs) that we eat. In this energy system, it is the breakdown of glycogen in the muscle that supplies the energy necessary to manufacture ATP.

7. Lactic Acid… is a toxic waste product produced when there is insufficient oxygen available during muscle contraction. It is a major source of muscle fatigue. inhibits the electrical impulse at the neuromuscular juncture which allows muscles to contract. increases the fluid viscosity (thickness) within the muscles making it difficult for the muscle fibres to slide across each other (sliding filament theory of muscle contraction) Check the following website for more info on sliding filament theory: http://education.adam.com/products/ipie/iguide/Sliding_Filament_Theory.pdf

8. What is Anaerobic? * When high intensity work is being performed, oxygen (O2) is not available in sufficient quantities to meet the muscles’ needs ?the Immediate Energy System and the Lactic Acid Energy System are anaerobic. They take place without the presence of oxygen.

9. 3. The Aerobic Energy System *When sub-maximal/moderate intensity work is being performed, oxygen is available in sufficient amounts to meet the muscles’ needs. This is when the re-synthesis of ATP is at its most efficient. ie. for every molecule of glycogen broken down, 39 molecules of ATP are re-formed. The process by which glycogen is broken down by the muscles in the presence of oxygen is called aerobic glycolysis.

10. For the Lab Rats…

11. The Energy Continuum The contribution of each energy system in supplying the bulk of the ATP necessary for a particular activity depends on the nature of the activity.

14. The 4 Areas of the Energy Continuum During an activity, once a certain performance time, or intensity, is reached, that specific system is no longer the dominant supplier of ATP.

15. Energy System Contribution to various activities (Fox et al, 1993)

16. Fuel for Exercise Our bodies utilise 3 types of fuel: Carbohydrates as derived from glucose and its stored form, glycogen (stored in muscles and liver and transported via the blood). Once a cell has reached its limit of glycogen storage, the excess sugars are converted and stored as fat. ATP is produced more quickly from carbohydrates than other fuel sources. CHO stores are finite and can be exhausted. 2. Fats (triglycerides) which are stored in muscles and adipose tissue. Stored fat represents the body’s most plentiful source of potential energy. Triglycerides break down into Free Fatty Acids (lipolysis) which then enter the muscle cells via the blood and combine with the aerobic glycolysis process to provide ATP. Proteins which are broken down into amino acids in the digestive system and transported via the blood. Generally, protein is the last of the fuel sources to be called upon during exercise.

17. “FATS BURN IN A CARBOHYDRATE FLAME!” Certain processes within CHO breakdown are required for fats to continue on their own path to breakdown and energy provision ? CHOs are utlised before fats in supplying energy for ATP re-synthesis Two factors determine the type of fuel used by the body during physical activity: Diet Intensity and duration of the activity As intensity increases, carbohydrates become the dominant fuel source. As activity duration increases, fat becomes the dominant fuel. WHY?

18. During prolonged exercise, CHO usage is initially less than fat usage, but this reverses as the duration of the activity increases. Question: When might CHOs return as the dominant fuel source during a marathon run?

19. How do we Measure Intensity? Essentially, the simplest method of measuring intensity involves the Heart Rate (HR), measured in beats per minute (bpm). Traditionally, a person’s theoretical maximum heart rate (MHR) is calculated as 220 – age (in years) HRmax = 220 – age (y) Generally, very high intensity work = 95-100% of MHR (the Immediate energy system) High Intensity work = 80-95% of MHR (Lactic Acid energy system) Sub-maximal intensity work = < 80% of MHR ** While neither sex or race affect the MHR calculation, levels of fitness and specific activities can!!

20. CV response to exercise Considering that the blood is essential to providing the required components to the muscles for the ATP synthesis and re-synthesis process to occur and that this process during prolonged physical activity occurs in the presence of oxygen, the cardio-vascular system’s response to exercise is of great importance. Firstly, we shall look at the major components of the CV system and then their response to physical activity:

25. The Oxygen Transport System: Terminology Cardiac Output (Q): the amount of blood pumped by the heart in 1 minute (litres/minute). Q = Stroke Volume (SV) ? Heart Rate (bpm) (amount of blood the heart pumps per beat) During exercise, the working muscles can receive up to 70% of the cardiac output.

26. Arteriovenous Oxygen Difference(a-vO2 Difference): Reflects how much oxygen the muscle extracts from the arterial blood. The more oxygen extracted, the less oxygen there will be in venous blood ? the a-vO2 Difference increases. Oxygen Uptake (VO2): the volume of oxygen transported and consumed by the body. VO2 = SV ? HR ? a-vO2 Difference Cardiac Output (Q) Since the aerobic energy system provides the bulk of ATP supply during prolonged exercise, the ability of an athlete’s body to provide as much O2 to the working muscles, and for these muscles to fully utilise this O2, is of great importance. The Oxygen Transport System: Terminology

27. Maximal Oxygen Uptake (VO2 max): the maximum amount of oxygen capable of being transported to and consumed by the working muscles. This is considered the benchmark measurement for endurance athletes VO2max is measured in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min) as this takes the size of a person (thus, the size of their lungs etc.) into account when measuring their aerobic capacity. Minute Ventilation (VE): the amount of new air that is inspired in one minute. VE = Tidal volume ? breaths/minute (air volume inspired or expired per breath)

28. O2 Transport System - Trained vs Untrained

29. Fatigue & Recovery As exercise intensity ?’s, so too does the heart rate and the VO2. At some point, however, the VO2 will stop rising despite the exercise intensity continuing to increase. This is VO2 Max – the maximal amount of oxygen that the body’s muscles can consume and representing the maximal amount of ATP that the aerobic system can produce.

30. Earlier, we used the % of Maximum Heart Rate as a guide to the use of particular energy systems. This allows the intensity of a physical activity to be gauged as well. The intensity and duration of the activity will also provide information about how the performer will fatigue and recover. For example: a 40m sprint will demand maximum intensity ? 95-100% MHR ? utilise the Immediate energy system for its ATP supply. The muscles will have used most of its phosphagen (muscle’s creatine phosphate levels) stores and will require approx. 2-3 mins to replenish these. How best to do this is helpful to know.

31. Diagram: Phosphagen replenishment after 10 mins continuous sub-maximal cycling using inactive rest. How much faster might the phosphagen stores be depleted if the cycling was at a higher intensity? Note the speed with which almost ¾ of the phosphagen stores are replenished. With inactive rest, 98% phosphagen replenishment took approx. 3-4 mins

33. Lactic Acid & Recovery When performing work of high intensity (approx. 80-95% of MHR), the process of anaerobic glycolysis will kick in to provide the bulk of required ATP. This process is the breaking down of stored carbohydrates when oxygen is not present. One of its major by-products is lactic acid. Lactic acid build-up is one of the two major causes of fatigue during exercise (the other being glycogen depletion – “hitting the wall”). During prolonged activity, the cardio-vascular system will gradually lose ground in providing oxygen to the working muscles. This means that instead of the pyruvic acid, which results from glycolysis, breaking down into water and CO2 (as it does in the aerobic system), it produces lactic acid which leaks into the muscles and impairs contraction. The more intense the activity, the faster this will occur ? the faster fatigue will occur. The oxygen present in the aerobic energy system (prolonged sub-maximal exercise) takes lactic acid’s impairing effects out of the equation. Because oxygen removes lactic acid, a warm-down (continuous,sub-maximal post-event activity ie. using the aerobic energy system) is so useful in recovering from high intensity activity. See the next diagram…

35. The Anaerobic Threshold

37. The Oxygen Debt OR Excess Post-exercise Oxygen Consumption (EPOC) cont’d As the body settles into a rhythm after the initial burst of activity (sub-maximal intensity), the body’s VO2 reaches steady state (after 3-5 mins) whereby the aerobic system is supplying all of the ATP needs for the muscles. The other systems are operating, however, the O2 is metabolising any lactic acid produced into pyruvic acid which then re-enters the aerobic system’s processes. The Immediate energy system at this time is contributing essentially no ATP. As can be seen in the previous diagram, VO2 does not immediately fall to resting levels once exercise ends. Instead, it gradually decreases to resting levels. This excess post-exercise oxygen Consumption (EPOC) during recovery is usually more than the oxygen deficit and is thought to be the body’s way of re-paying the “oxygen debt” with some “interest”. (can’t escape the banks, eh?).