Lactic Acid Energy System 3j6y4v

LACTIC ACID ENERGY SYSTEM AND AEROBIC ENERGY SYSTEM

LACTIC ACID ENERGY SYSTEM Source of Fuel – The lactic acid energy system uses carbohydrates (CHO) as its only source of fuel and relies on anaerobic glycolysis for its production of ATP. Glycolysis is the breakdown of glucose to produce ATP. In anaerobic glycolysis the glucose (sourced from glycogen in the muscle or glucose in the blood) is turned into lactic acid as it produces ATP.

EFFICIENCY OF ATP PRODUCTION This system produces ATP at a fast rate and can produce a lot of ATP. The lactic acid system produces 2 ATP for each glucose molecule it breaks down, however, it also produces lactic acid in the process.

DURATION THAT THE SYSTEM CAN OPERATE The lactic acid system lasts between 30 seconds and 3 minutes depending on the intensity. The less intense the activity the longer it will last, because it will be producing lactic acid at a slower rate at the lower intensity levels.

CAUSE OF FATIGUE The cause of fatigue in the lactic acid system is the build up of pyruvic acid in the muscle. Pyruvic acid is made up of two molecules; pyruvate and a hydrogen ion (H+). Without oxygen the body converts the pyruvate and two H+ to lactate. This helps to reduce the acidity of the muscle and allows anaerobic glycolysis to last longer, as the lactate is removed from the muscle and taken to the liver where it is converted to a useful fuel source such as glucose. However, in continued high intensity activity the lactate cannot be removed fast enough, which results in a build up of pyruvic acid. It is specifically the build up of the H+ within the muscle that causes fatigue. It does this by increasing the acidity of the muscle and causing the enzymes needed for anaerobic glycolysis to slow down.

BY-PRODUCTS OF ENERGY PRODUCTION The main by-product of the lactic acid system is pyruvic acid (pyruvate and H+). This by-product is then converted to lactate and transported out of the muscle to the liver to be converted to glucose.

PROCESS AND RATE OF RECOVERY The process of recovery once fatigue has occurred requires oxygen. Pyruvic acid in the presence of oxygen will be converted to acetyl coenzyme A, which is then broken down through the Krebs cycle to produce more ATP. Without oxygen it is converted to lactate and removed from the muscle and taken to the liver to be converted into glucose. This process can take anywhere between 30 and 60 min.

EXAMPLES The lactic acid energy system is the dominant system in sports, which require a high intensity for longer than 10 seconds. Sports such as 200m or 400m run, or 50m and 100m swim are highly reliant on the lactic acid system. Other times when it is used would include repeated high intensity activities during other sports such as tennis running back and forth with small breaks in-between, repeated tackles in rugby or an extended piece of high intensity in any other sport such as a full-back going forward in an attack and then having to retreat in soccer.

AEROBIC ENERGY SYSTEM Source of Fuel – The aerobic system can use CHO, fats, and protein as its source of fuel, though protein is used sparingly. The aerobic system uses aerobic glycolysis, the Krebs cycle and the electron transport chain in its production of ATP. It is the presence of oxygen, which allows this energy system to use these various fuel sources.

EFFICIENCY OF ATP PRODUCTION – The aerobic system is very efficient in producing ATP. It produces 38 ATP molecules per glucose, but the rate of production is medium and cannot cope with the higher intensity levels.

DURATION THAT THE SYSTEM CAN OPERATE This energy system can produce ATP continuously for well over an hour. In fact, it may not have a limit as long as fuel sources can be found (you will die if this energy system cannot be used). However, your muscle glycogen will deplete after about an hour of exercise, which will result in an increased need for oxygen as fats becomes the dominant fuel source and uses more oxygen per ATP produced than CHO.

CAUSE OF FATIGUE Though this system does not need to stop, a reduction in intensity will occur when CHO stores deplete. Since fats require more oxygen to produce ATP than CHO, an athlete will normally decrease their intensity when their main fuel source switches from CHO to fats. This is often called hitting the wall. If it is possible for the athlete to transport oxygen at a faster rate than they are when their CHO run out, then their body will adjust and bring the extra oxygen to the muscle. This will mean an increase in respiration and possibly an increase in heart rate and cardiac output, but it will allow the athlete to continue to perform.

BY-PRODUCTS OF ENERGY PRODUCTION – The aerobic system produces water and carbon dioxide as by-products in its production of ATP. Water can build up in the muscle and cause stiffness and a sort of “swelling” if exercise is continued at a high enough intensity for long enough, but generally it is transferred out of the muscle and into the blood as water is being lost through sweat during exercise. The carbon dioxide is taken out of the muscle and expired by the lungs into the atmosphere. Carbon dioxide, if not removed can cause fatigue, but is normally removed well.

PROCESS AND RATE OF RECOVERY Recovery for the aerobic system is about restoring fuel stores to their pre-exercise levels. This requires the ingestion, digestion and transportation of the fuel and can take between 12 and 48 hours depending on the intensity and duration of the aerobic performance.

EXAMPLES The aerobic system is the dominant system for any sport or activity that lasts more than 3 minutes. This includes most team sports such as netball, soccer, rugby, and AFL as well as many individual sports such as 1500m swimming, marathon running, cycling, triathlons, tennis and iron mans.