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ENERGY SYSTEMS
Having a base understanding of the body’s energy systems is important for selecting the best type of
drills and training for a cycling workout. Prior to the contraction or shortening of a muscle, adenosine
tri-phosphate
(ATP), which is stored or synthesized in muscle cells, is broken down so energy can be
released. ATP is immediately available to the muscles and contributes to the three main energy systems
called the ATP-CP, Anaerobic Lactic Acid and the Aerobic Systems. The contribution to ATP synthesis
varies depending on the duration and intensity of an activity being performed. For example, short intense
exercise uses the ATP-CP system for energy and longer duration activities rely on the Aerobic System.
1. ATP-CP
• Used during maximal exercise intensity >90% max HR (heart rate)
• Can be initiated instantaneously
• Depleted within approximately 10 to 20 seconds
• Limited supply in the muscles
2. ANAEROBIC LACTIC ACID SYSTEM
• Used during high-intensity exercise >80% max HR (heart rate)
• No oxygen is required so it can be initiated quickly
• Depleted within 60 to 180 seconds
• Lactate by-product of the lactic acid system changes the pH in the muscle, causing fatigue
3. AEROBIC SYSTEM
• Used during lower-intensity exercise <80% max HR (heart rate)
• Oxygen is required to produce ATP in order to sustain muscle contraction during
long-duration and endurance exercises
• Activities lasting longer than three minutes
ATP-CP Anaerobic Lactic Acid Aerobic
Energy Source Stored within the muscle
ATP is produced in Highly effective energy
absence of O2 (oxygen) production using O2 (oxygen)
Power Output High Medium Low
Activation Speed Immediate Fast Slow
Time 10–20 seconds 1–3 minutes 2 hours+
Fuel Source CP & ATP Carbohydrates Fats
Peak Power 1 sec 20 sec 2–3 min
Maintain Peak Power 10 sec 30 sec 3 min
Capacity 6–30 sec 30 sec–3 min 2+ hours
Full Recovery 3 min 1–2 hours 24–48 hours
Half Recovery 20–30 sec 15–20 min 5–6 hours
PHYSIOLOGY
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