Energy Systems: Aerobic & Anaerobic
Understand the systems, how your body creates power, and how each system influences training and performance.
What It Is
Your body produces energy through two primary systems:
1. Aerobic System (With Oxygen)
This system uses oxygen to convert carbohydrates and fats into energy. It fuels long-duration, steady efforts and is the cornerstone of endurance performance. It’s efficient, stable, and supports sustained power output for hours.
2. Anaerobic System (Without Oxygen)
This system produces energy without relying on oxygen and fuels short, high-intensity bursts—sprints, surges, and steep climbs. It relies on fast-burning energy stores and produces lactate as a byproduct.
Both systems work together during every ride, but the balance shifts depending on intensity. This is a really important nuance that most amateurs miss. Even if you're riding in Zone 2, your anaerobic system is active! It just is contributing a de minimis amount of the energy.
ELI5 Version
Think of your body like a hybrid car:
- Aerobic = the efficient engine that runs all day.
- Anaerobic = the turbo boost you use for climbs, sprints, attacks, breakaways, etc.
Why It Matters
- Drives all training zones, from Zone 1 recovery to all-out sprints.
- Explains how different workouts create different adaptations.
- Aerobic development raises LT1 and LT2, improving all-day power. This is also referred to as shifting the lactate curve, which can you read about more here.
- Anaerobic development boosts sprinting, climbing punch, and race responses.
- Helps athletes pace efforts more effectively based on metabolic demands.
Practical Use
- Build your aerobic system with Zone 2, Tempo, and Sweet Spot work.
- Improve anaerobic capacity with short, high-power intervals (Zones 4, 5 and 6).
- Use VO₂ Max training to strengthen the bridge between aerobic and anaerobic systems.
- Track heart rate and power on your bike computer for real-time feedback.
- Use lactate thresholds to understand when each system becomes dominant and track your training progress over time.
Training is a dose and response relationship. We "dose" the body with stimulus in different zones to tune the use of both energy systems for the demands of our race or general life and fitness goals.