Energy systems Energy for muscular contraction during exercise comes from the splitting of a high energy compound (ATP). 3 systems – adenosine triphospate (ATP PC), Lactic acid system and the aerobic system ATP stored in very small amounts in the muscles (enough to provide for maximal contraction for about 1 second. All 3 energy systems are activated at the start of exercise, with the relative contribution being determined by the intensity and duration of exercise. All 3 work together.

Foods and their conversion to energy Food is taken into the body as chemical energy and converted into mechanical energy in the form of muscular contractions and movement. Food – digested, broken down, nutrients absorbed, waste to the bowel. Nutrients carried off via the bloodstream. Some fuel is used immediately whilst others is stored around other parts of the body. Carbohydrates, fats and protein are the only sources of food energy and fuel.

Carbohydrates Sugars and starches found in fruit, cereal, bread, pastas and vegetables. Body’s preferred source of fuel, particularly during exercise. Carbohydrates are the primary energy source during anaerobic exercise of high intensity and short duration. Carbohydrates are broken down and stored as glucose in the blood and glycogen in the muscles and liver. Excess carbo’s are stored around the body as adipose tissue.(fat tissue)

Fats Fats include butter, oils, nuts. Fat is the body’s preferred source of fuel at rest. More oxygen is required by the body to use fat as a fuel than to use carbo’s to produce ATP. Fats have the capacity to produce much more ATP than carbo’s however the conversion rate is much less efficient since they require much more oxygen to produce and equivalent amount of ATP. Fatty acids are stored in the blood, triglycerides in the muscles and excess fats are stored as adipose tissue around the body.

Protein Protein include meat, fish, poultry, dairy, eggs and lentils. Protein is used for growth and repair of the body and as fuel source in extreme situations. Body only uses protein as energy source when glycogen and fat sources have already been depleted. Ie. marathon or starvation

Food fuels at rest and during exercise At rest – aerobic energy system utilises both fats (2/3) and carbohydrates (1/3) as preferred fuel because they do not generate by products which cause fatigue. During exercise – both anaerobic and aerobic systems contribute energy for ATP resynthesis during exercise. Several factors determine which system is the major contributor of energy – duration and intensity as well as training. Short duration ie 100m sprint – anaerobic system supply most of the required energy (carbo’s) For prolonged submaximal (low intensity) aerobic system is preferred system with carbo’s initially. As glycogen stores depleted, fat mainly becomes the energy source.

Energy systems – what are they? 2 anaerobic systems are ATP-PC system and the lactic acid system – does not depend upon the transportation of oxygen to the working muscles Aerobic system is produced with oxygen.

3 Energy systems ATP-PC system (alatacid, creatine phosphate or phosphogen system) Lactic acid system (anaerobic glycolysis or lactic acid system) Aerobic system (oxygen system) 3 basic pathways responsible for the resynthesis or rebuilding of ATP (energy supply). Depends upon : duration and intensity of exercise, how urgent energy is required, whether oxygen is present.

3 energy systems At rest demands for energy are low and can be met aerobically. Exercise increases the demand for ATP because we can not increase our oxygen intake and transport to the working muscles as rapidly as is required by explosive activities, our body calls upon the 2 anaerobic systems in the early (initial) stages of exercise to supply ATP. If the exercise is longer in duration and less intense, then the aerobic energy system will be called upon to supply most of the energy.

ATP-PC system Phosphocreatine (PC) (also known as creatine phosphate)- high energy fuel stored in small amounts in muscles. Broken down to ADP+P (adenosine diphosphate + phosphate) during muscle contraction. As rapidly as ATP is broken down to enable movement, it is being reformed by the energy released when PC is broken down. Advantage – immediate Disadvantage – limited by amount of PC stored in muscle Used at onset of work (short duration/high intensity/explosive activities) maximum high intensity activity for 5 secs about 50% of PC stores depleted. Ie short sprints, field events, spiking in volleyball. Maximum contractions at maximal effort for 10-15 secs 30 secs rest for 50% replenishment 8-10 mins for 100% replenishment

Lactic Acid System Anaerobic glycolysis system – carbo’s are broken down to glucose and stored at the muscles and liver in the form of glycogen. ATP must be reformed and replaced from ADP and Pi (a free Phosphate molecule0, but again, this requires energy. This energy is obtained from glycogen. Glycolysis is the process of breaking down glycogen. Because oxygen is not present, the glycogen is not totally broken down and a toxic waste called lactic acid is formed. This causes muscular fatigue.The lactic acid system provides a stopgap until sufficient oxygen can be transported to the working muscles for the aerobic system to become the major contributor. Lactic acid system is activated at the start of intense exercise. Peak power from this system is reached between 10 -15 seconds will last for 2 -3 mins before fatigue. Anaerobic threshold is a term used to describe the point at which the anaerobic production of energy leads to the accumulation of lactic acid in the blood, usually occurring at around 85% max heart rate during exercise.

Aerobic System Uses oxygen and is the most powerful (has greatest ability to supply ATP) Aerobic energy system will be the major energy contributor for extended endurance activities that remain below 85% Aerobic system uses the Krebs cycle and the electron transport chain to produce ATP.

Aerobic System 3 stages in aerobic energy production, responsible for the release of energy. Stage 1 – fats and carbo’s broken down to release energy. Fats stored as triglycerides, are broken down releasing small amounts of energy for basic body functions and low intensity activities. Carbo’s (also used in lactic acid system) are used to provide energy in the aerobic system. Difference is that sufficient oxygen is supplied - glycogen broken down to glucose and pyruvic acid with energy made available for ATP resynthesis. (Aerobic glycolysis). No toxic waste ie lactic acid.

Aerobic System Stage 2 – krebs cycle – involves pyruvic acid being broken down into carbon dioxide with further energy being released to resynthesise ATP.

Aerobic System Stage 3 – electron transport stage – involves water (perspiration), heat and large amounts of ATP being released. Aerobic system preferentially breaks down carbo’s rather than fats to release energy, however fats can produce more ATP than carbo’s but require more oxygen to produce an equivalent amount of ATP. Aerobic system is fatigue resistant. Primary source for endurance activities. Aerobic production of energy occurs within the muscle cell, this involves the breakdown of carbo’s and happens in the mitochondria cell.