Fuel and Flow with Jess
A Run Vault series on nutrition and hydration for performance

Fuel and Flow with Jess

Why do long runs feel harder in the back end?

If you have ever set out on a long run feeling strong, only to find the last few kilometres feel like a battle, you are not imagining it. For most runners, the back end of a long run almost always feels harder, and there are some good reasons why.

Physiological fatigue

As the kilometres add up, your muscles naturally get tired. Early on, your stride feels light and springy, but as fatigue builds your body has to work harder just to hold the same pace.

This is partly because your body starts to run low on glycogen, the primary fuel source for running. When glycogen runs out, you feel sluggish, heavy, and drained of energy.

Fatigue can also change your form. Many runners lean forward or start overstriding without realising it, which makes running less efficient and adds to the struggle.

Nutrition and hydration

If you head out under fuelled, or fail to take in enough carbohydrates and fluids along the way, your energy will dip earlier and the last stretch will feel much tougher. Dehydration makes things worse because your heart has to work harder to pump blood, which raises your effort levels.

Even bigger picture factors, like low iron levels or not eating enough day to day, can leave you feeling more tired before you have even started.

This is where the right supplements can make all the difference.

• Carbohydrate gels, chews, and sports drinks provide quick, accessible energy when glycogen runs low.
• Electrolyte powders or tablets help replace sodium and minerals lost through sweat, especially in hot or humid conditions.
• Daily nutrition support, like an iron supplement or multivitamin, can help if you are prone to fatigue or struggling to meet your needs through food alone.

Featured products from this article

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• Explore hydration and electrolytes
• Race day fuelling essentials

Psychological factors

Your mind also gets a workout during long runs. At the start you are fresh and focused, but as the run goes on mental fatigue sets in. Discomfort feels louder, and looking ahead at how far you still have to go can make every kilometre drag.

Add in hot weather, wind, poor sleep, or a busy training week, and it is no wonder the back end feels like a grind.

The good news

The good news is that there are plenty of ways to make it easier.

• Fuel smart: for runs over 60 minutes, aim for around 60 to 90 grams of carbohydrate per hour using gels, sports drink, lollies, or chews.
• Stay hydrated: start your run well hydrated and sip water or electrolytes along the way.
• Build gradually: increase your long run distance and duration step by step so your body adapts.
• Strength and mobility: support your running form with exercises that help you hold good technique even when fatigued.
• Mental strategies: break the run into smaller chunks, focus on one kilometre at a time, or use a simple mantra to keep yourself moving forward.

Need help fuelling your running?

Struggling with long runs or fuelling well for your training? A sports nutritionist can help you dial in your nutrition, hydration, and recovery so those tough kilometres feel smoother.

Book a sports nutrition chat with Jess

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