The common mistakes athletes make in fuelling during an endurance race

You’re eight hours into an endurance race. You’re pushing on, pushing hard, feeling strong. You’ve trained for this and you’re executing it perfectly.

You are an ultra-racer!

But then you feel it. You know what I’m talking about.

That feeling of fullness in your upper abdomen. The first burp. You start to lose the taste for food. You sense a prickling of nausea, which soon becomes full-blown.

Now you can’t get food in. In fact, it insists on coming out!

Your energy stores are being depleted mile after mile, and you’ve still got a long way to go.

Panic mode sets in.

DAMN!

Your stomach is now running the race and you… well, you’re a passenger on the gut train.

I’m writing this blog for one reason only: to help you fall a little in love with your stomach, or at least develop a little more respect for it.

Maybe then you’ll treat it better and make less mistakes in fuelling.

Your stomach is doing a remarkable job

‘Down the hatch.’ ‘Get it in you.’

Many athletes fire food in with little thought of chewing it first. You simply expect your stomach to go along with it and do its thang, whatever that thang is.

Well, your stomach’s thang is really quite remarkable.

It has a pressure pump, a rhythmic mixing pump, a grinder and a filter. It carefully coordinates the receipt of food and fluid with different physical and chemical compositions. It mechanically mixes and chemically breaks down what you eat, grinding solid food into smaller particles before passing it through a final filtering process.

All the while, it is responding to signals from your nervous system and hormones, regulating when and how quickly its contents are released through the pyloric sphincter, the opening into the small intestine.

Without you feeling a thing, small amounts of this beautifully processed mixture, now known as chyme, are released into the small intestine, where digestion and absorption continue and the nutrients begin their journey towards supporting your energy needs and sustaining life.

Thank you, stomach!

It all works remarkably well until… you get in the way.

Your stomach has a job to do. Racing makes it harder

Before we get to the things you throw ‘down the hatch’, let’s remember what your stomach is already dealing with.

If you’re cycling, you’ve folded yourself over the handlebars and your body is diverting blood supply towards your working muscles. If you’re an ultra-runner, you’re flying up mountainsides, with countless foot strikes potentially disrupting the comfort and rhythm of digestion.

Those add up, you know!

During prolonged exercise, blood flow to the digestive system can fall significantly, particularly when intensity is high, you’re dehydrated or you’re racing in the heat. Digestion is having to operate in less-than-ideal conditions.

But that’s okay. Your stomach is made of tough stuff.

It can expand considerably to accommodate food and fluid without a proportional increase in pressure. You’ve got some room to play with.

But that flexible, tough little organ has rules.

And understanding them can make a real difference to your race.

Rule 1: Fluids and solids behave differently

Water and relatively dilute carbohydrate drinks generally leave the stomach more readily than concentrated drinks or large amounts of solid food. Temperature can also influence gastric emptying, although the effect varies with the circumstances.

Solids have a different journey.

Food needs to be broken down mechanically and mixed with digestive secretions before it can pass efficiently into the small intestine. Chewing does some of that work before the food even reaches your stomach.

The smaller and easier to digest the food is, the less work your stomach has to do.

Larger solid particles take longer to process. Some material may remain in the stomach until later, when the digestive system has a better opportunity to deal with it.

That’s not necessarily a problem when you’re sitting at home after dinner. During an ultra, when you’re asking your body to keep producing energy for hours on end, it can become a problem.

And if you insist on throwing large, poorly chewed solids down that hatch, you’re increasing the workload of an organ that’s already under pressure.

Your gut-brain connection is a powerful thing. Signals between your digestive system and nervous system help regulate motility and can contribute to nausea and vomiting when things go wrong.

You may find yourself bringing your food back up, or desperately searching for a hedge.

Lovely stuff.

Are you falling in love yet?

You see, I love an organ with clear rules. An organ that can stand up for itself. An organ that refuses to be nutritionally bullied.

Rule 2: More carbohydrate isn’t always better

One industry that doesn’t always seem to love the stomach is the sports nutrition marketing industry.

What it does love is highly concentrated fluids, gels and foods.

We’ve been sold the need for energy. Lots of it, and instantly.

We’ve heard the recommendations for 90g of carbohydrate per hour. Then 120g per hour.

And to be fair, higher carbohydrate intakes can be useful for some athletes in some circumstances, particularly when they have trained their gut to tolerate them.

But an endurance race isn’t a controlled laboratory setting.

It’s also one thing to get carbohydrate into the stomach and quite another to get it through the digestive system comfortably and absorb it.

Your stomach is an expandable space, but its capacity to accommodate food and fluid doesn’t mean it can empty them at the rate you need.

You might get away with a highly concentrated fuelling strategy for a few hours. But what happens when you’re eight, twelve or twenty-four hours into a race?

That’s where we need to pay attention.

Rule 3: Concentration matters

Let’s look at carbohydrate drinks.

A drink containing 5% carbohydrate provides 5g of carbohydrate per 100ml. If you’re drinking 500ml per hour, that’s 25g of carbohydrate.

A relatively dilute drink like this will generally leave the stomach more readily than a much more concentrated solution, although gastric emptying depends on several factors, not carbohydrate concentration alone.

Research on gastric emptying helps us understand these differences. But it can’t reproduce every condition you’ll meet during an endurance race.

Heat, dehydration, wind, cold, sleep deprivation, changes in intensity and the sheer duration of the effort all complicate the picture.

You folks are operating outside the neat boundaries of the laboratory.

Nevertheless, a steady supply of carbohydrate from a drink that you can tolerate comfortably can be a useful starting point for an ultra-cyclist or runner.

Now imagine a much more concentrated drink.

A 10% carbohydrate solution contains 10g per 100ml. As carbohydrate concentration increases, gastric emptying can slow, particularly when the drink is also energy-dense or contains other ingredients that affect digestion.

The exact response varies, but the practical point is important: a drink that delivers more carbohydrate per mouthful isn’t necessarily a drink that delivers more usable energy over the course of a race.

Now add concentrated energy bars and gels on top of that.

If the rate at which you’re putting food and fluid in consistently exceeds the rate at which your digestive system can process it, contents can accumulate. Fullness, nausea, bloating and a growing reluctance to eat may follow.

That exquisite dance of pressure and flow can grind to a halt.

And so can your performance.

Five practical ways to work with your stomach

For the love of God, and your newly discovered appreciation of your stomach, here are five things to consider.

Because the adage ‘no guts, no glory’ communicates a searing metaphorical truth for the endurance cyclist, runner and adventure racer.

1. Choose digestible foods and chew them well.

Where solid food works for you, look for options that are easy to digest and break them into small, bite-sized pieces. Chew them properly before swallowing.

There are lots of options. The trick is finding the ones that work for you, your race and your digestive system.

Call me!

2. Pay attention to the concentration of your carbohydrate drink.

A carbohydrate drink in the region of 5–8% can be a useful starting point for some athletes. That means 5–8g of carbohydrate per 100ml.

Your ideal concentration will depend on how much you’re drinking, how much carbohydrate you need and how well you tolerate the combination.

And if someone is handing you a bottle, make sure it’s chilled if you find that more palatable. Cold drinks can be easier to take in during some conditions, although individual responses vary.

3. Don’t overlook fluid-based foods.

Fluids can provide carbohydrate without requiring the same mechanical breakdown as solid food.

Depending on the product and your individual tolerance, options might include chocolate milk, squeezable foods, blended soups or smoothies.

These aren’t interchangeable, and not all will suit every stage of a race. But variety can be useful when chewing becomes unappealing or your stomach starts to feel overloaded.

4. Find the carbohydrate intake you can actually use.

Instead of blindly following a prescribed amount of carbohydrate per hour, start figuring out what you can tolerate comfortably while maintaining your performance.

We all have to experiment with that. No exceptions.

An intake in the region of 0.5–1g of carbohydrate per kilogram of body mass per hour may be a starting point for some athletes, but it isn’t a universal target. Requirements depend on the duration and intensity of the event, your energy needs, your gut training and the fuelling strategy you’re using.

The goal isn’t simply to get carbohydrate into your stomach. It’s to find a sustainable intake that supports your performance without overwhelming your digestive system.

And that takes practice.

5. Use gels wisely.

Gels are a convenient way to carry carbohydrate, but they’re often highly concentrated. A gel containing 25g of carbohydrate may deliver that amount in a very small volume, so check the product and its instructions.

Some gels are designed to be taken with water; others have different formulations. Follow the guidance for the product you’re using and consider the overall concentration of your fuelling strategy, rather than looking at each item in isolation.

And here’s a bonus tip from a fellow BarrUltra racer: an ice-cold gel goes down a lot easier.

That makes sense to me. If it helps you take in your fuel comfortably, it deserves consideration.

Your fuelling strategy needs to work for the whole race

As endurance athletes, you desperately need a steady supply of energy. We have to be creative.

It’s one of the many challenges of endurance racing, but it’s also one where my expertise comes in handy.

There are different fuelling strategies that balance the ongoing need for energy with what your digestive system can comfortably process. Carbohydrate cycling (no pun intended) is just one possibility.

We can also work on gut training, gradually increasing carbohydrate intake where appropriate, experimenting with different food and fluid combinations, and adjusting the timing and composition of your fuelling.

The aim is to develop a strategy that works with your physiology, your event and your individual tolerance, rather than forcing your stomach to follow a number on a packet.

Because your stomach is part of your performance team. It deserves a place in the planning.

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f you’re sick (literally) of seeing great performances limited by stomach issues, let’s talk.

I’ve spent years working with endurance athletes to develop fuelling strategies that balance energy requirements with the realities of racing.

Let’s find an approach that works for you, so you can spend less time negotiating with your stomach and more time working towards that finish line — and, perhaps, that podium.