Running long distances — whether it’s a half marathon, marathon, or ultra — isn’t only about fitness. It’s about managing your body’s energy systems so you can keep moving mile after mile without “hitting the wall.” Endurance comes from the way runners fuel, pace, hydrate, and train their bodies to efficiently use energy.

 

Glycogen: The Primary Fuel

What it is: Glycogen is stored carbohydrate in muscles and the liver.

Science: Your body can only store about 90–120 minutes worth of glycogen at moderate intensity. Without refuelling, depletion leads to fatigue, often called “the wall.”

Strategy:

  • Carbohydrate-loading before long races maximizes glycogen stores.
  • Mid-run fuelling (energy gels, chews, or sports drinks) replenishes glycogen and delays fatigue.

The Role of Fat Oxidation

What it is: Fat is the body’s largest energy reserve. Even lean runners carry tens of thousands of calories in fat stores.

Science: At lower intensities, the aerobic system burns more fat; at higher intensities, carbs dominate.

Strategy: Long, steady training runs teach the body to use fat more efficiently, sparing glycogen for later miles.

Hydration and Electrolytes

Why it matters: Sweat losses deplete fluids and electrolytes (sodium, potassium, magnesium). Dehydration of just 2% body weight impairs endurance and increases fatigue.

Strategy:

  • Drink steadily during long runs.
  • Include electrolytes to replace sodium and reduce cramp risk.
  •  Practice a hydration plan in training, not just on race day.

Pacing for Endurance

Why it matters: Starting too fast burns glycogen rapidly and makes fat utilization less efficient.

Science: Even pacing or negative splits (finishing faster) improve marathon performance compared to positive splits.

Strategy:

  • Run at a pace you can sustain, usually 60–75% of VO₂ max for long distances.
  • Train at “conversation pace” to build aerobic endurance.

Mid-Run Fuelling

Science: Consuming 30–60 g of carbs per hour (and up to 90 g for elite athletes) sustains blood glucose and delays fatigue.

Sources: Energy gels, chews, sports drinks, bananas, or other quick carbs.

Timing: Begin fuelling around 30–45 minutes into a long run, then every 30–45 minutes.

Training the Body for Efficiency

Long Runs: Build aerobic capacity and teach the body to manage energy reserves.

Tempo Runs: Improve lactate threshold, letting you sustain faster paces without fatigue.

Back-to-Back Long Runs (ultras): Teach mental and physical endurance.

“Gut Training”: Practicing fuelling during runs trains the digestive system to absorb carbs without discomfort.

Mental Energy

Endurance isn’t just physical. Mental focus, positive self-talk, and breaking the distance into smaller goals help sustain effort when fatigue sets in.

Science: Studies in sports psychology show that mental strategies reduce perceived exertion and improve pacing control.

Runners sustain energy over long distances by:

  • Fueling: Maximizing glycogen stores and refuelling mid-run.
  • Training: Building aerobic efficiency and fat utilization.
  • Hydration: Maintaining fluid and electrolyte balance.
  • Pacing: Conserving energy early to finish strong.
  • Mindset: Using mental resilience to push through fatigue.


Endurance isn’t about having unlimited energy — it’s about managing the energy you have wisely.