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Lesson 5 - Energy Systems

Definitions

The Basal Metabolic Rate (BMR) is the minimum amount of energy we require to stay alive, and is measured by monitoring oxygen and CO2 excretion.

ATP - Adenosine Triphosphate

ATP = ADP + P + Energy                      (ADP - Adenosine Diphospate)

Muscles store enough ATP for a 2 second contraction - this would supply sufficient energy for muscle contractions of short duration such as required for weight lifting, power lifting and shot putting.

Energy is released when a phosphate is broken off the ATP returning it to ADP. The cycle is continous, with ADP being converted back to ATP.

ATP breaks down to release energy when a nerve impulse stimulates a muscle fibre. The energy used from the breakdown of food joins a phosphate ion to ADP via a high energy bond.

The Energy Systems

There are three energy systems in the body that produce ATP. These are:

  • The aerobic system - releases energy slowly by using oxygen to breaking down glucose. It provides lots of long term energy suitable for every day activitites and endurance events. It can also break down fat to make ATP. As we get fitter, the amount of oxygen used by muscles increases. Energy is produced by the mitochondria (see lesson 4). By products are water, which we sweat or wee, and CO2, which we exhale.
  • The anaerobic systems, which produce energy without oxygen. These are:
    • The Phosphate System - the creatine phosphate molecule can be broken down quickly and is used to turn ADP back into ATP. The phosphate system is suitable for single or continuous short bursts of energy of around 10 seconds (as soon as ATP is broken down to ADP is it restored to ATP). This system would be used for events such as the long jump and javelin. The amount of creatine phosphate in muscles is limited, which is why athletes often use creatine phosphate supplements. This system is also called the ATP/PC system, the Alactate Anaerobic System and the ATP + CP system.
    • The Lactic Acid System - Provides energy for a longer duration than the Phosphate System, between 10 - 90 seconds, such as what would be required for a 100m swim, or a 400-800m run. Energy is derived from the fast break down of glucose from glycogen and blood sugar. Glycogen is stored in the liver and the muscles. When glycogen is broken down, it produces ATP and pyruvic acid. This process is called anaerobic glycolysis because the glycogen isn't fully broken down, but leaves a by product called Lactic Acid. When lactic acid accumulates in the muscles it results in muscle fatigue and weakness.
Energy System
What is broken down?
How long does the energy last?
Aerobic Glycogen, fat Long term
Phosphate Creatine Phosphate Up to 10s
Lactic Acid Glycogen Approx 1.5 mins

Factors Contributing to Muscle Fatigue

  1. Excessive activity - accumulation of lactic acid and CO2.
  2. Malnutrition - insufficient glucose to muscles.
  3. Cardiovascular anomalies - poor circulation affecting delivery of glucose and oxygen, and the removal of waste products.
  4. Respiratory anomalies - insufficient oxygen