KEY KNOWLEDGE KEY SKILLS Multiple fatigue mechanisms including fuel depletion, metabolic by-products and thermo-regulation and their collective contribution to muscular fatigue under conditions of varied intensity and duration Recovery strategies, including active and passive types, used to facilitate the body’s return to a pre-exercise state The take up, transport and utilisation of oxygen during exercise by considering the principles oxygen deficit and steady state, and recovery mechanisms during oxygen debt/EPOC. Explain how the energy systems work together to supply energy during physical activity as well energy system contribution to active and passive recoveries Understand how using the energy systems under varied exercise intensities and conditions will contribute to fatigue at various levels. Compare and contrast appropriate recovery methods suited to offset and delay fatigue, facilitate optimal performance and return the body to pre-exercise levels. © Cengage Learning Australia 2011

Fatigue is caused by many factors = multi factorial © Cengage Learning Australia 2011

What is fatigue? A decline in muscle force, contraction rate and muscular power. The onset/rate of development is dependent on: Exercise intensity Exercise duration Environment Nutritional status Training status

Central Fatigue – occurs when muscular function is decreased as a result of CNS impairment (occurs throughout the body) Peripheral Fatigue – when specific muscle function is disrupted at the muscle site(s) as a result of impaired internal muscle processes Levels of fatigue: Local (in specific muscle groups) General (throughout the whole body) Chronic (unhealthy breakdown of immune system – long term fatigue)

1. Fuel depletion Depletion of: ATP and PC Glycogen (Hypoglycaemia)

(i) Depletion of ATP and then PC main cause of fatigue for anaerobic /high intensity/short duration based events. Causes switch from ATP-PC to anaerobic glycolysis  reduced rate of ATP resynthesis (and therefore muscle contractions) This occurs in events where the ATP-PC system is dominant / there is not enough passive recovery time in between each exercise bout. This is an example of peripheral fatigue, as the depletion is happening inside a specific muscle

Fuel depletion – ATP and PC ATP is an immediate energy source but very limited (two seconds supply) PC occurs in limited supply at the muscles (10-12 seconds supply) These are quick to supply ATP but just as quickly depleted – then muscle glycogen and liver glycogen is used in larger amounts. © Cengage Learning Australia 2011

(ii) Depletion of Glycogen (hypoglycaemia) – Peripheral fatigue 1. Use muscle glycogen 2. Use liver glycogen (Gluconeogenesis: glucose can be made in the liver from amino acids, fats, lactate and other non CHO substances Glucose is stored as glycogen in the muscle and liver (four/five times more in the muscle). The liver storage acts as a buffer for blood glucose levels) During hypoglycaemia: Body resorts to fats – exercise intensity must decrease because more O2 is needed to break the fats down and it is a slower process This occurs in aerobic/endurance events lasting greater than 90mins Central Fatigue (whole body) Reduced blood glucose levels impairs CNS activity 1. Brain (decision making) 2. Muscle activation (force)

Fuel depletion – glycogen and fats Muscle glycogen is used first during aerobic activities and then liver glycogen. Once liver glycogen runs low (hypoglycaemia) muscles increasingly use blood-borne fats and then stored fats. The rate of ATP resynthesis decreases quickly (50 – 100 % slower) once the body switches to fats as the main fuel source – this causes slowed performances. Proteins are called upon when fat stores run low which leads to an even greater slowing down. © Cengage Learning Australia 2011

2. Accumulation of Metabolic by-products ATP-PC System ADP Pi Anaerobic Glycolysis: Lactic Acid (H+ ions) Aerobic/endurance events past LIP:

ATP-PC System Inorganic phosphate (Pi) and adenosine diphosphate (ADP) ATP  ADP + Pi Effect of Pi The accumulation of Pi decreases the force of a muscle contraction by reducing the amount of Ca2+ that can be released via the sodium-potassium pump This is an example of peripheral fatigue (occurs in a specific muscle)

Effect of ADP ADP controls the speed of the actin-myosin detachment during a contraction. It’s accumulation causes: a decrease in the maximal velocity of a contraction a reduction in power output

Anaerobic Glycolysis (occurs during 100m/200m sprint, 50m swim) H+ ions in plasma and muscle During anaerobic glycolysis, for each lactate molecule, one hydrogen ion is formed. H+ ions not lactate make the muscle acidic  decreases muscle function by slowly down enzyme activity and the breakdown of glucose Aerobic Glycolysis (occurs during high intensity aerobic exercise (above LIP) e.g. 1500m run, 800m swim) Once LIP has been exceeded, H+ ion accumulation due to: An increased contribution from anaerobic glycolysis (causing greater production of lactate and H + ions) An inability to breakdown/remove the lactate and H + ions that are accumulating.

3. Thermoregulatory Central Fatigue Occurs when the body tries to maintain a constant body temperature (thermoregulation) Cold environment (Hypothermia) Examples: cross-country events, mountain climbing, deep sea diving Shivering (energy expenditure) Reduced blood flow to the muscles (more to the core)

Hot environment (Hyperthermia) Examples: Hawaii ironman, AFL match, Melbourne marathon Heat production – mainly from exercising muscles (Chemical  Mechanical energy) - by product Decrease blood flow to the muscles (more to skin) Sweating - fluid & electrolyte loss (dehydration) and decrease in blood plasma and blood volume – causes decrease in SV Losing 2-3% of body weight through sweating impairs thermoregulation, muscle endurance and neuromuscular coordination Losing 6% = unconsciousness High heat and humidity greatly limits heat loss, causing you to sweat even more