Introduction to Energy Systems Lesson

Lesson Overview

• The ATP-PC System: Short, Powerful Bursts
• ATP: The Energy Currency
• The Lactic Acid System: Medium Duration, High Intensity
• The Aerobic System: Long Duration, Steady Intensity
• Beep Test and Aerobic Efficiency
• Comparison Table of Energy Systems
• Fuel Use by Energy Systems
• Intensity Zones and Energy System Use
• Energy System Activation During a Marathon

Every movement we make, from blinking an eye to sprinting down a track, requires energy. Our body has specialized systems that produce and manage this energy efficiently. These are known as energy systems. 

Each system supports different types of activity, depending on how long and how intense the activity is. Understanding these systems helps explain how the body powers various forms of physical activity.

The ATP-PC System: Short, Powerful Bursts

This system provides immediate energy for very short, explosive efforts.

• Duration: 0 to 10 seconds
• Intensity: Maximal (e.g., sprinting, shot put)
• Fuel source: Stored ATP and creatine phosphate (CP)
• Oxygen use: Anaerobic (no oxygen needed)
• By-products: None

This system is used when performing quick, high-power activities such as shot put. It is powerful but limited in duration.

ATP: The Energy Currency

ATP (adenosine triphosphate) is the molecule that stores and delivers energy within cells. It consists of:

• An adenosine molecule
• A ribose sugar
• Three phosphate groups

When a phosphate group is removed, energy is released. When one is added to ADP (adenosine diphosphate), energy is stored again.

The Lactic Acid System: Medium Duration, High Intensity

This system takes over when intense activity lasts beyond 10 seconds but not more than 2 minutes.

• Duration: 10 seconds to 2 minutes
• Intensity: High
• Fuel source: Glucose (from glycogen in muscles)
• Oxygen use: Anaerobic
• By-product: Lactic acid

This system is dominant in activities like 400m sprints. It enables continued intense effort but leads to muscle fatigue due to lactic acid buildup.

Impact of Lactic Acid

• Causes a burning sensation
• Reduces muscle efficiency
• Decreases overall performance

Associated Fitness Component

• Muscular endurance: Needed to perform repeated efforts under fatigue.

The Aerobic System: Long Duration, Steady Intensity

This is the most efficient energy system, powering sustained activities with moderate effort.

• Duration: More than 2 minutes
• Intensity: Sub-maximal (less than 85% of max heart rate)
• Fuel source: Carbohydrates, fats, and proteins
• Oxygen use: Aerobic (requires oxygen)
• By-products: Carbon dioxide and water

Cross-country skiing and marathon running depend heavily on this system.

Fitness Component Matched

• Cardio-respiratory endurance: Reflects the ability to maintain aerobic activity over time.

Additional Roles

• Helps remove lactic acid post intense activity
• Supports recovery between efforts

Beep Test and Aerobic Efficiency

The beep test measures how efficiently the aerobic system works by increasing intensity gradually. Good performance indicates strong cardio-respiratory endurance.

Comparison Table of Energy Systems

This table highlights the key differences between the three energy systems in terms of their function, fuel use, and performance characteristics.

Take This Quiz:

Energy System Trivia Quiz! MCQ

Fuel Use by Energy Systems

This table summarizes the primary fuel types used by each energy system to generate energy.

Intensity Zones and Energy System Use

This table shows how different levels of exercise intensity correspond to the dominant energy system in use.

Energy System Activation During a Marathon

• Start (first seconds): ATP-PC for initial acceleration
• Early minutes: Lactic acid system as aerobic warms up
• Majority of race: Aerobic system dominates due to long duration and steady pace

Understanding these systems helps explain how your body meets energy demands across different types of physical activity. Each system plays a role, often overlapping with others to ensure that energy needs are met efficiently and appropriately based on the task at hand.