PART 3: WHAT FUEL DOES YOUR BODY USE?

THE THREE KEY COMPONENTS OF AEROBIC ENERGY PRODUCTION

RECAP: So far in the Blog series…

• Part 1: We covered Oxygen Supply —how your heart and lungs deliver oxygen to your muscles.
• Part 2: We broke down Oxygen Utilization —how your mitochondria use that oxygen to create energy.

Now its time to answer  What kind of fuel does your body actually burn to create that energy?

Because understanding fuel selection isn’t just for elite athletes—it’s key for anyone who wants better endurance, fewer energy crashes, and faster recovery.

THE TWO MAIN FUEL SOURCES

Your body can use multiple types of fuel, but during aerobic activity, it mainly runs on:

1. Carbohydrates (Carbs)

• Stored in the muscles and liver as glycogen
• Used during moderate to high-intensity activity
• Burns quickly and efficiently
• Supports speed, power, and high-intensity intervals

As coach Jason Brown often notes in his energy systems programming:
Carbs are the primary fuel when the intensity goes up—and they’re critical for strength and power athletes too.

2. Fat

• Stored in fat cells all over the body—even lean athletes have plenty
• Burns slowly and steadily
• Used most during low-intensity, steady-state efforts like Zone 2 training
• Requires more oxygen and time to turn into energy

According to Joel Jamieson , author of Ultimate MMA Conditioning :
The ability to efficiently burn fat is one of the most important markers of long-term endurance performance and recovery.

 HOW YOUR BODY DECIDES WHICH FUEL TO USE

Your body doesn’t just switch between fat and carbs—it blends them.
The exact mix depends on:

WHY FUEL USAGE MATTERS

Training your body to burn fat more efficiently has serious benefits:

✅ You conserve limited glycogen (carbs)

• Your body has a small carb tank. Once it’s empty, fatigue hits hard.

✅ You increase endurance

• More fat usage = less chance of “hitting the wall”

✅ You recover faster

• Fat-burning athletes experience less metabolic stress after workouts

CARBS STILL MATTER

Don’t make the mistake of thinking carbs are “bad.”
They’re essential for:

• High-intensity workouts
• Competition and race efforts
• Strength and power training

Jason Brown emphasizes this in his hybrid programs:

“You need enough carbs to fuel your CNS and power output, especially if you’re lifting heavy or sprinting.”

NOTE:

Fuel before and after your hard sessions. For low-intensity Zone 2? You can sometimes train fasted to boost fat adaptation—just don’t overdo it.

TRAINING TO BURN FAT BETTER

Here’s how to make your body more metabolically flexible (i.e., better at switching between fuel sources):

✅ Zone 2 Endurance Work

• Builds mitochondria (your energy engines)
• Boosts capillary density
• Improves fat oxidation
  Joel Jamieson often prescribes this as the base of any well-rounded conditioning plan.

✅ Controlled Fasted Training

• Light workouts (like walking or easy cycling) before breakfast
• Can increase fat-burning enzymes—but should be done sparingly and strategically

✅ Nutrient Timing

• Fuel with carbs around workouts
• Don’t overload on sugar the rest of the day

PUTTING IT ALL TOGETHER

Let’s review the full picture of aerobic energy:

When all three are trained together, you build a high-performance aerobic engine that lasts longer, works smarter, and recovers faster.

References: