Energy systems

• The energy system that is used depends on the intensity, duration and type of exercise
• The chemical energy of a cell is supplied by the breakdown of adenosine triphosphate (ADP)
• There are 3 ways of resynthesising ATP: ATP/PC system, glycolytic/anaerobic glycolysis and aerobic glycolysis.
• ATP levels fall and ADP levels increase, this stimulates the release of creatine kinase. Creatine kinase breaks down the PC bond releasing energy. This energy is then coupled to the re-synthesis of ADP to ATP.
• Anaerobic glycolysis: glucose is supplied as an energy fuel from the digestion of carbohydrate. Decrease in PC stores activates the enzyme glycogen phosphorylase to break down glycogen into glucose through glycolysis.
• During glycolysis, the enzyme phosphofructokinase (PFK) initiates the partial break down of glucose into pyruvate acid. As there is insufficient oxygen, the pyruvic acid is broken down in to lactate by the enzyme lactate dehydrogenase in to lactate and H+ ions. 2 ATP are produced.
• Aerobic glycolysis: pyruvic acid is diverted further in the aerobic system and combines with coenzyme A. This forms Acetyl CoA and releases Co2.
• Stage 2 - Kreb's cycle: Acetyl CoA from stage 1 combines with oxaloacetic acid to form citric acid. This is further broken down in a series of complex reactions in the matrix of mitochondria where four events take place. Co2 and water is produced and removed via the lungs, energy produced to re-synthesise 2 ATP, oxaloacetic acid is regenerated so the process continues.
• Stage 3 - Electron transport chain: hydrogen is carried to the ETC by hydrogen carriers NAD and FAD. This occurs in the cristae folds of the mitochondria. The hydrogen splits into hydrogen ions and electrons and these are charged with potential energy. The hydrogen ions are oxidised to form water while providing energy to resynthesise ATP. 34 ATP formed.
• Beta oxidation: triglycerides are broken down by enzymes termed lipases into three free fatty acids and glycerol. Used as energy fuel in aerobic system. FFA's converted to acetyl CoA, which is broken down by the Kreb's cycle and ETC through beta-oxidation.
• OBLA - onset blood lactate accumulation. Occurs at 4 mmole/l.
• OBLA will continue to increase if exercise intensity is maintained/ increased. Lactate threshold can be increased through anaerobic training, prolonging the point at which OBLA is reached.
• PC availability - used for very high intensity activity. Limited but available at start and after a period of recovery during exercise. If intensity starts too high then the PC stores will be depleted and high-intensity explosive activity can be sustained. Conserved through pacing.
• Oxygen availability - aerobic system can provide energy to re-synthesise ATP if there is sufficient oxygen available. If oxygen levels fall below the demand for the exercise, the aerobic system threshold is reached and glycolytic system begins to break down the glucose anaerobically to resynthesise ATP. High intensity = break down glycogen. Low intensity = break down FFAs and glycogen.
• Glycogen availability - major fuel for first 20 mins. Requires less oxygen and therefore quicker to break down than FFAs to allow a higher aerobic intensity of exercise.
• FFAs availability - after two hours, FFAs have to be used for aerobic energy production and can bring on onset of fatigue (hitting the wall) if intensity is not reduced. Require 15% more oxygen to break them down, resulting in lower intensities needed.
• The more aerobically fit the performer, the more efficient their respiratory/CV systems are to take in and transport and use oxygen to break down glycogen and FFAs aerobically to resynthesise ATP. Untrained athlete would reach OBLA at 50-50%, aerobic trained would reach at 85-90%. Anaerobic athlete will increase ATP/PC and glycogen stores which would increase tolerance to lactate, increasing threshold of both ATP/PC and glycolytic systems.
• Exercise induced muscle damage (EIMD) - immediately following bouts of strenuous exercise in which the body is not accustomed to where significant muscle damage has been caused.
• EIMD can be managed by gradually introducing eccentric muscle actions over time and performing a prior bout of eccentric exercise reduces severity of symptoms.
• Delayed Onset Muscle Soreness - body increasing inflammation as a protective response to tiny micro tears caused as a result of strenuous, high intensity exercise. 24-48 hours post exercise.
• DOMS can be managed by cool down, massage, compression clothing and ice baths
• Exercise Post-exercise Oxygen Consumption (EPOC) is the increase in oxygen consumption after exercise to restore body to pre-exercise state.
• Fast alactacid component - restoration of phosphogen stores (re-phosphorylation). Restore muscles store of ATP and PC. Helps replenish muscle stores myglobin/haemoglobin. Requires approx 3-4L of oxygen. Takes 3 mins to fully restore ATP/PC stores. 50% restored in 30 secs, 75% in 60 secs.
• Slow lactacid component - takes place after 3 minutes. Responsible for removal/re-conversion of lactate. Lactate is converted back to pyruvate to be used in the Kreb's cycle. Supports elevated metabolic functions taking place after exercise, namely: high body temps remain for several hours after exercise, hormones remain in blood, cardiac output remains high helping to reduce temperature.
• Slow component - requires approximately 5-8L of O2 and can remove lactate from between 1-24 hours after exercise. Dependent upon exercise intensity and levels of lactate removal required. Anaerobic exercise increases oxygen deficit and OBLA, producing higher levels of lactate. Results in a higher EPOC required as it will take longer for oxygen consumption to return to pre-exercise levels.
• Glycogen replenishment - utilise 2 hour window of opportunity. continue replenishment 10-12 hours post exercise but complete recovery can take up to 48 hours to fully replenish. High carb diet can restore glycogen fully within the first two hours of recovery.
• Recovery - interval training is more efficient than continuous work at adapting energy systems as it increases the intensity of training and can be adapted to target specific energy systems.
• For speed improvements, ATP/PC systems work ratio may be less than 10 secs and relief ratio longer (1:3) allowing time for ATP and PC stores to fully recover (2-3 mins). For VO2 max, the work relief ratio is greater in duration/intensity (1:1) - helps reduce OBLA.
• Priming - manipulating warm up to speed up O2 consumption. Speeding up how quickly the aerobic energy pathway is activated, by increasing: intensity of warm up (bout of high intensity), allocated recovery time. Used as a way to delay onset of lactate accumulation and therefore reaching anaerobic threshold.
• Effects of priming: increased oxygen uptake, increased enzyme activity of anaerobic and aerobic enzymes, increases rate at which energy systems work, oxidation of lactate occurs during recovery phase to initiate steady state activity, heart rate remains higher so oxygen uptake is increased at start of exercise.