Have you ever wondered how your body powers through a sprint on the bike, a heavy gym session, or a long distance run? The secret lies in the interplay of three energy systems that work seamlessly to fuel your muscles during exercise. In this post, I'll break down these systems and explore how they contribute to performance at different intensities and durations.
The Three Energy Systems
Phosphagen System/ATP-PC (Immediate Energy)
The Phosphagen system is the blue line above in the graph, this provides instant energy.
Duration: 0–10 seconds
Intensity: High (e.g, sprints, heavy lifts such as olympic lifts)
Energy Source: Stored ATP and creatine phosphate
The Phosphagen system is your body’s first responder when exercise begins. Making it essential for short, explosive activities like a 100-meter sprint or a maximum deadlift. However, its energy reserves are limited, depleting quickly within 10 to 15 seconds.
The Work:Rest ratio here is 1:12 to 1:20.
Glycolytic System (Short-Term Energy)
The Glycolytic system is the red line above in the graph.
Duration: 10–60 seconds
Intensity: Moderate to high (e.g, a 400-meter run or a high-intensity interval)
Energy Source: Glucose (via anaerobic glycolysis)
When the Phosphagen system runs out, the glycolytic system takes over. This system breaks down glucose to produce ATP, but it does so without oxygen, leading to the production of lactate. While it’s effective for sustaining moderate duration efforts, the accumulation of lactate can contribute to muscle fatigue.
The Work:Rest ratio here is 1:3 to 1:5
Oxidative System (Long-Term Energy)
The Oxidative system is the green line above in the graph.
Duration: 60 seconds and beyond
Intensity: Low to moderate (e.g, long distance running, cycling)
Energy Source: Carbohydrates and fats (via aerobic metabolism)
For activities lasting more than a minute, the oxidative system becomes the primary energy provider. Unlike the other systems, it relies on oxygen to produce ATP and can sustain energy production for hours. Which is ideal for endurance events like marathons or long bike sessions.
The Work:Rest ratio here is 1:1 to 1:3
How Energy Systems Overlap
While each system has its specific time frame, they don’t work in isolation. Instead, they overlap to ensure your body can adapt to the demands of exercise. At the start of an activity the phosphagen system dominates, providing a quick amount of energy. The glycolytic system then kicks in to sustain the effort. Finally, for longer duration events, the oxidative system takes over and becomes the primary source of energy.
I hope this helped provide a brief overview of each system and its function. For any other specific areas you'd like covered, get in touch.
Thanks for reading,
Graham
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