4STARTER ANSWERThe bus is headed to the right, otherwise we would see the entrance door!
5FACTORS AFFECTING THE ENERGY SYSTEM USED Explain how the following affects the energy system used by athletes:Exercise Intensity and DurationEnergy System ThresholdO2 Transport/SupplyFood/Fuel availableEnzyme Activation LevelsFitness Level
6EXERCISE INTENSITY AND DURATION A combination of exercise intensity and duration can determine the predominant energy system(s) being used. When exercise intensity is anaerobic (high intensity, short duration), then the ATP/PC and LA Systems will be predominant. If the exercise intensity is aerobic (medium/low intensity, long duration), then the Aerobic System will be predominant.
7EXERCISE INTENSITY AND DURATION When the aerobic system cannot supply energy quick enough, it has to use the LA system to continue to provide energy for re-synthesis of ATP. During high intensities lactate production will start to accumulate above resting levels. This is termed Lactate Threshold. When blood lactate levels reach 4mmol/L (normal resting levels are 1-2mmol/L), the exercise intensity is referred to as ‘the Onset of Blood Lactate Accumulation’ (OBLA). OBLA continues to increase if exercise intensity is maintained or increased and will cause muscle fatigue.
8EXERCISE INTENSITY AND DURATION After training the intensity level for lactate threshold is increased and this will delay the point at which OBLA is reached and therefore increases the potential duration/threshold of the LA energy System.
9ENERGY SYSTEM THRESHOLD The Threshold for any system is ‘the point at which that energy system is unable to provide energy.’ Or ‘the point at which one energy system is taken over by another as the predominant energy system to provide energy for ATP re-synthesis.’
10ENERGY SYSTEM THRESHOLD Performance DurationEnergy System(s) Involved (predominant in bold)Practical ExampleLess than 10 secondsATP/PCTriple Jump/100m sprint10-90 secondsLAm sprint100m swin90 secs – 3 minsAerobicBoxing (3 min rounds)800/1500m3+ minsLow impact aerobics classMarathon
11ENERGY SYSTEM THRESHOLD The energy system threshold alters in response to a combination of both intensity and duration of exercise and will not always go through each energy system in turn. For example, a cyclist cycling at a low intensity will be using the Aerobic System, although when going up hill they may exceed the intensity threshold of the aerobic system and the lactic acid system will take over as the predominant energy system. In team games, players will switch between the three energy systems.
12O2 TRANSPORT/SUPPLYIf there is O2 present then the aerobic system can provide energy to re-synthesise ATP. If O2 supplies falls below that demanded by the exercise then the aerobic system threshold is met and the lactic acid system will start to break down glucose anaerobically.
13FOOD/FUEL AVAILABLEIf the body has sufficient stores of PC, it is able to use the ATP/PC system for very high intensity, short duration activity/movements. PC stores are limited, but are available at the start and after recovery during exercise. If exercise starts too high then PC stores will quickly deplete and exercise at that intensity cannot be sustained. PC stores can be conserved by pacing and re-synthesising PC stores during recovery periods using spare energy from the aerobic system.
14FOOD/FUEL AVAILABLEGlycogen is the major fuel for the first 20 minutes of exercise. This is due to O2 supplies being limited as it takes 2-3 minutes for the cardiovascular system to supply sufficient O2. As well as glycogen being readily available in the muscles, requires less O2 and is easier to break down than FFA’s
15FOOD/FUEL AVAILABLEAfter about minutes there is a greater breakdown of fats alongside glycogen as the energy fuel. FFA’s are a more efficient fuel than glycogen, but require 15% more O2. If a performer has larger muscle/liver glycogen store, then they can perform work aerobically at a higher intensity.
16FOOD/FUEL AVAILABLEGlycogen stores become nearly depleted after about two hours, then FFA’s have to be used for aerobic energy production, and unless exercise intensity is reduced it can bring on the sudden onset of fatigue (‘hitting the wall’). Once OBLA is reached the body has insufficient O2 available to burn FFA’s and will then have to break down glycogen ‘anaerobically’ to re-synthesise ATP
17ENZYME ACTIVATION LEVELS Factors Affecting Enzyme Activation for the Energy SystemsActivating FactorReleases Controlling Enzyme(s)Activating Energy SystemIncrease in ADP; decrease in ATPCreatine KinasePCDecrease in PCPFKLA SystemIncrease in adrenalin; decrease in insulinAerobic System
18FITNESS LEVELThe more aerobically fit the performer, the more efficient their cardiovascular and respiratory systems are. Aerobic athletes have also shown that they can start to use FFA’s earlier during sub-maximal exercise, which conserves glycogen stores. The overall effect is that the aerobic threshold in terms of intensity and duration can be increased as the lactate threshold/OBLA would be delayed.
19FITNESS LEVELA typical untrained athlete would reach OBLA at about 50-56% of their VO2 max, whereas an aerobic-trained athlete would not reach OBLA until about 85-90% of their VO2 max.An anaerobic-trained athlete will increase their ATP/PC, glycogen stores, anaerobic enzymes and tolerance to lactic acid. All of this would increase the threshold of both ATP/PC and Lactic Acid Systems.
20Summarise the factors that affect the energy system used PLENARYSummarise the factors that affect the energy system used