There is a persistent myth in running culture that bonking is reserved for marathons, ultras, or epic long runs gone wrong. The idea is simple: short run equals low risk. No fuel needed.
Reality is less forgiving.
Many runners hit the wall on runs under 60 minutes and walk away confused, frustrated, or blaming fitness. The real culprit is usually not distance. It is intensity.
Glycogen Depletion Happens Faster Than You Think
Muscle glycogen is not a marathon-only resource. It is a limited fuel tank that drains in proportion to how hard you press the accelerator.
At easy aerobic paces, fat oxidation contributes meaningfully to energy supply. As intensity rises, carbohydrate dependence increases sharply. Once you move above moderate effort, glycogen becomes the dominant fuel.
This means a hard 45-minute session can be more glycogen-demanding than a slow 90-minute jog.
Add in factors like:
- Low-carb availability from previous sessions
- Poor recovery fueling
- Early-morning runs after an overnight fast
and the tank can be closer to empty than you realize before you even start.
Intensity Beats Duration Every Time
Runners tend to think in minutes and kilometers. The body thinks in watts, pace relative to threshold, and metabolic cost.
Tempo runs, progression runs, hill repeats, and interval sessions all push carbohydrate usage upward. Even when the total duration is short, the internal load is high.
A 10 km steady run at threshold pace can deplete glycogen faster than an easy long run because:
- Glycolysis is dominant
- Fat contribution is suppressed
- Lactate turnover increases carbohydrate demand
Distance does not protect you. Intensity overrides it.
Tempo Runs and Intervals Are Fueling Traps
These sessions are especially deceptive because they feel “too short to fuel.”
Common mistakes:
- Skipping pre-run carbohydrates
- Treating a quality session like an easy jog
- Saving fuel “for race day”
The result is a familiar pattern:
Strong first half, fading legs, rising heart rate, and a sudden feeling of heaviness or dizziness that feels disproportionate to the distance covered.
This is not weakness. It is predictable physiology.
The Core Takeaway
If the run has quality, it needs fuel - regardless of distance.
Fueling is not reserved for long runs. It is a performance tool that supports:
- Power output
- Neuromuscular coordination
- Session quality and consistency
- Long-term adaptation
Ignoring fuel on hard days does not make you tougher. It makes your training less effective.
Train with intention. Fuel with intention. Distance alone does not tell the full story, effort does.
Excerpt / Meta description:
Runners often bonk on short runs not because of distance, but because intensity drives glycogen depletion faster than expected. If a session has quality, it requires fuel, no matter how short it looks on paper.