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6.5 Anaerobic vs Aerobic Metabolism

The chart below compares anaerobic and aerobic metabolic pathways. As shown, each system plays a distinct role depending on the duration of activity and the resources available. Generally speaking, the anaerobic pathways, ATP-CP and Glycolysis, supply the body with ATP and recovery relatively quickly but only provide us enough ATP for short bouts of strenuous activity. Aerobic pathways, however, act differently by providing long-term energy and recovery on an ongoing basis, reducing the system’s recovery duration to nearly zero, all while supplying the body with more efficient ATP production.

Comparing Anaerobic & Aerobic Pathways

Anaerobic
Energy Source Energy Duration System Recovery Duration Net ATP Gain
ATP-CP Pathway 10 to 5 seconds 2 to 5 minutes 1 ATP per CP molecule
Glycolysis 1 to 3 minutes Several minutes to 2 hours 2 ATP per glucose molecule
Aerobic
Energy Source Energy Duration System Recovery Duration Net ATP Gain
Krebs Cycle 2 minutes – sustained Ongoing, no full “shutdown” 2 ATP per glucose molecule
ETC Sustained Ongoing, oxygen-dependent 32 to 34 ATP per glucose molecule

Fitness Fact

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“Yoga” by Undraw, Undraw License

What Energy System am I using?

It is a common misconception that the body only utilizes one energy system at a given time. While you may be engaging in physical activity that can easily be associated with a specific energy system based on the demand it puts on the body, the body is complex and relies on multiple systems in order to maintain ATP levels. For example, when you are running and start to get tired, it is easy to believe that the body “switches” from cellular respiration to glycolysis; however, this is simply untrue. In reality, both aerobic and anaerobic systems are working to meet physical demands for energy.

Energy Systems in Action During Physical Activity

The graph below shows what energy systems are predominantly active during exercise over time. This includes ATP-CP pathway, glycolysis, the Krebs cycle and the ETC.

Energy System in Action During Physical Action versus ATP Usage graph
Graph showing ATP usage by different energy systems over 180 seconds of exercise. The ATP-CP system peaks early around 10 seconds, glycolysis follows and declines after 60 seconds, while the Krebs cycle and electron transport chain gradually increase and dominate after 90 seconds, reflecting a shift from anaerobic to aerobic metabolism. See source below. Modified by Koen Liddiard

Energy System Contribution During Exercise Graph: OpenAI. (2025). ChatGPT. [Large language model]. https://chat.openai.com/chat Prompt: “I need a graph type image that shows what energy systems are prodomiently active during exercise duration over time. I need it to include the ATP-CP pathway, glycolysis, the Krebs cycle and the Electron transport chain.”

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The Foundations of Human Movement and Physical Fitness Copyright © 2025 by A.J. Stephen; Sarah Fraser; and Connor Dalton is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.