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The Energy Systems

Participate in any physical activity, the muscles of the body require energy. This energy is obtained through three distinct energy systems:

The Anaerobic Alactic Energy System

This system provides immediate energy for short bursts (1-15 seconds) of maximal-intensity exercise. The system uses energy stored in the muscle, requires no oxygen (anaerobic) and produces no lactic acid.

Development of this system is important in strength, speed and power events.

The Anaerobic Lactic Energy System

The anaerobic lactic system takes over just before the anaerobic alactic system runs out. This system plays a predominant role in providing energy for moderate- to high-intensity exercise from 10 seconds to three minutes. The system uses energy from the breakdown of carbohydrates (glucose) and requires no oxygen (anaerobic). A limiting factor of this system, however, is the production of lactic acid as a by-product of the energy production. This system also depletes the body's carbohydrate stores extremely quickly. Development of this system contributes to high-intensity endurance and power events.



The Aerobic Energy System

The aerobic energy system is the predominant energy supplier for low- to moderate-intensity exercise. During a high-intensity "race-pace" event, this system starts to predominate after about 2-3 minutes of exercise and is the main source of energy after 3-4 minutes. The system breaks down both carbohydrates and fats for energy, and requires oxygen (aerobic). There is generally no lactic acid produced.

The three energy systems and their percentage contribution to total energy output during all-out exercise of different durations(Adapted from McArdle, Katch and Katch, Exercise Physiology - Energy, Nutrition and Human Performance, 4th Ed, Williams and Wilkins, Baltimore.)

During a rugby match all the energy systems are called upon.

  1. Anaerobic Alactic: jumping in lineout
  2. Anaerobic Lactic: short sprints
  3. Aerobic: sustained support play