Fueling Your Movement: Energy Systems for Runners, Walkers & Ruckers

How your body powers you through everything from 5Ks to ultramarathons

With the 2025-2026 running season approaching fast, many of you are likely planning which events to tackle. Whether you're eyeing the Austin Solstice Circuit in July or the Colorado River Run in November, understanding how your body powers through these different races can make all the difference in your training.

Photo by Sid Suratia on Unsplash

But have you ever wondered what's actually happening inside your body during these different race distances? Why do you feel so different running a quick 5K versus grinding through a marathon? And why does training consistently transform what once felt impossible into something manageable?

Today, we're diving into the fascinating science of your body's energy systems—the biological machinery that powers every stride you take. Understanding this science isn't just academic; it's practical knowledge that can transform how you train and race.

The Tale of Two Energy Systems

Your body is equipped with two primary methods for producing energy:

The Aerobic System: Your Endurance Engine

Think of your aerobic system as your hybrid car's efficient mode—it requires oxygen, operates at a steady pace, and can go the distance.

COACH'S CORNER: Your aerobic system powers 90% of your marathon effort during the Colorado River Run. That's why long runs are non-negotiable!

This system:

• Burns carbohydrates, fats, and sometimes proteins for fuel

• Produces tons of energy from each bit of fuel

• Powers you through those long Sunday runs and marathon efforts

• Takes a bit to fully activate but can sustain you for hours

When you're running the longer distances at the Colorado River Run, you're primarily in aerobic territory.

The Anaerobic System: Your Turbo Boost

Your anaerobic system is like hitting the sports mode in your car—it's powerful, fast-acting, but burns through fuel quickly.

This system:

• Produces energy without needing oxygen (hence "anaerobic")

• Generates only 2-3 ATP per glucose molecule (less efficient but faster)

• Powers high-intensity efforts like sprints, hills, and finishing kicks

• Can only sustain maximum output for seconds to minutes

When you're flying down the final stretch of the Austin Solstice Circuit 5K or pushing through a challenging section on the Colorado River Run course, you're tapping into anaerobic power.

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Energy Systems for Rucking, Walking & Hiking

Not everyone will be running! If you're planning to ruck the Colorado River Run or tackle the Heart of Hill Country Challenge by hiking, here's how energy systems work for you: