Energy Systems

Fuel for Muscle Contraction Carbohydrates, fats and protein are broken down to form an energy rich molecule called Adenosine Triphosphate (ATP).

Fuel for Muscle Contraction When a muscle is stimulated, enzymes are released which cause one of the phosphate bonds to be broken, thus releasing energy

Fuel for Muscle Contraction There is only a small amount of ATP stored in the muscles (enough for one or two contractions). The body must use 3 different energy systems to supply more ATP.

Food as the Source of Fuel Carbohydrates (CHO) –After digestion are broken down into blood glucose –Some CHO is also broken down into glycogen which is stored in the liver and muscles –Blood and muscle glycogen are used before liver glycogen –Provides 16 Kj energy per gram

Food as the Source of Fuel Fats –After digestion, dietary fats are found in the blood as free fatty acids and triglycerides. –Excess fat is stored in adipose tissue and muscle –Fat is used as fuel in low to moderate activity exercise of a long duration –Yields 37Kj per gram energy.

Food as the Source of Fuel Protein –Under normal circumstances, protein is not used by the body to resynthesise ATP. –Only used in starvation type conditions. –Protein is important for other body repair and maintenance processes. –Yields 17Kj per gram energy.

Energy Systems So, we need ways to resynthesise (put back together) the ATP in muscles. There are two general types: aerobic (with oxygen) and anaerobic (without oxygen).

Energy Systems The ATP/PC system –Also called alactacid system or phosphate system –The first part of this system is the resident ATP molecules which are always ready for break down. –The second part involves the breakdown of another molecule called Phosphocreatine (or Creatine Phospate) PC.

Energy Systems PC C + P + energy this energy then resynthesises ATP ADP + P + energy ATP

Energy Sytems There is only enough PC in the muscles for about 10 seconds of maximal or near maximal exercise. No waste product produced No oxygen used (anaerobic) Examples of activities which predominantly utilise ATP/PC system include 100m sprint, high jump.

Energy Systems The Lactic Acid System (anaerobic glycolysis) For high intensity activities lasting between 10 and 90 seconds. Body breaks down muscle stores of glycogen (CHO) No oxygen used

Energy Systems Muscle glycogen Pyruvic Acid ATP Lactic Acid Muscle Fatigue ADP

Energy Systems Provides ATP very quickly but is inefficient because of lactic acid build up in muscles and blood. Lactic acid contributes to muscle fatigue and exhaustion. Lactic Acid can take up to 2 hours to be removed from bloodstream. Typical event is 400m run.

Energy Systems Aerobic Energy System –After 2-3 minutes of exercise the body is able to provide enough oxygen for a the aerobic energy system to provide a continuous supply of ATP. –Oxygen + muscle glycogen pyruvic acid + carbon dioxide + water + energy

Energy Systems Efficient because water used for cooling, CO2 is breathed out and oxygen limits build up of lactic acid. Fats can also be “burned” using aerobic system Complex system of chemical reactions are used (aerobic glycolysis, Krebs cycle, and Electron transport system). All reactions occur within special cells called mitochondria.

Energy Systems Lower intensity (up to 70% maximum) Typical events include marathon, cross country skiing.

Energy Systems The Relationship Between Systems –The systems do NOT work in isolation –They each have a contribution in most activities…the proportion of that contribution varies depending upon the duration and intensity.

Energy Systems –Eg a marathon runner will initially use ATP/PC during start and the lactic acid system during the first minute or two before the aerobic system “clicks in”. They may also use the two anaerobic systems for a couple of bursts of speed during the race.

Energy Systems