How Your Body Fuels Performance
When you lace up your shoes and head out for a run—whether it’s a 100m sprint, a 10K race, or an ultra-marathon—your body taps into an intricate system of energy production to keep you moving. These energy systems determine how fast, how far, and how efficiently you can go. As a runner, understanding them can help you train smarter, race better, and avoid the dreaded bonk.
Let’s break down the three primary energy systems that fuel your running:
1. ATP-PC System (Phosphagen System): The Power Surge
- Duration: 0–10 seconds
- Used for: Explosive, high-intensity efforts like sprints, jumping, and short bursts of speed
- Fuel source: Stored ATP and phosphocreatine (PC)
This is your body’s emergency generator—instant power, no oxygen required. It uses adenosine triphosphate (ATP) and phosphocreatine stored in your muscles to deliver a rapid burst of energy. Think: a 100m sprint or a sudden surge to overtake someone in the final stretch.
Training Tip: Hill sprints, short intervals (under 10 seconds), and plyometric drills develop this system.
The energy supplied by this system burns out fast. Once those immediate stores are gone, your body has to switch to the next system.
2. Anaerobic Glycolysis (Lactic Acid System): The Middle Gear
- Duration: 10 seconds – 2 minutes
- Used for: Middle-distance races (e.g. 400m to 800m), tempo surges
- Fuel source: Muscle glycogen (carbohydrate)
- By-product: Lactate and hydrogen ions (not the villain you think)
This system kicks in when the demand for energy outpaces your oxygen supply. It breaks down glycogen (stored carbs) to produce ATP quickly without oxygen, but with a cost: lactate builds up, along with acidic by-products that cause that familiar burning in your legs.
Despite the myth, lactic acid isn’t bad—in fact, lactate can be reused as fuel! But when production exceeds clearance, fatigue sets in.
Training Tip: Tempo runs, intervals between 30 seconds and 2 minutes, and lactate threshold workouts are key.
3. Aerobic System: The Endurance Engine
- Duration: 2 minutes – several hours
- Used for: Long-distance runs, marathons, ultras
- Fuel source: Carbohydrates and fat (with oxygen)
This is your body’s cruise control—slower to start but built for the long haul. It uses oxygen to convert glycogen and fat into ATP, providing steady energy over time.
This system becomes dominant during runs lasting longer than a few minutes and is essential for distance runners. The better your aerobic system, the more efficiently you can burn fat and spare glycogen—a key to avoiding hitting the wall.
Training Tip: Long runs, easy-paced runs, and aerobic threshold sessions enhance this system. Think “Zone 2” range training.
Why It Matters for Runners
Every energy system plays a role—even in a marathon, there are moments (like a hill surge or a sprint finish) where the ATP-PC system fires up. In Run Elite, Andrew Snow reminds us that running performance comes from “the sum of our muscle recruitment,” meaning that all three energy systems are engaged to varying degrees—often simultaneously. No matter your race distance, training all of them is essential to build a resilient, efficient, and adaptable engine.
| Race Distance | Primary Energy System |
| 100m–200m | ATP-PC |
| 400m–800m | Anaerobic Glycolysis |
| 1500m–5K | Mixed |
| 10K–Marathon | Aerobic |
| Ultra | Aerobic (with fat metabolism) |
Smart Training = Energy System Synergy
Training isn’t about hammering one gear—it’s about knowing when and how to shift between them. That’s where a coach can make a difference, by designing training that progressively targets thresholds, builds fatigue resistance, and enhances metabolic flexibility.
At A-Team Coaching, we assess your current fitness, goals, and race schedule to create a programme that systematically develops your energy systems for peak performance.
Final Thought
Running isn’t just legs and lungs—it’s biochemistry in motion. When you understand the body’s energy systems, you stop guessing and start training with purpose. Whether you’re chasing speed, endurance, or both, mastering how your body fuels movement is the secret to going further and faster.
Want to train with purpose?
Visit a-teamcoaching.com for personalised training plans that target every energy system and elevate your performance.