QT: Is Over-Fueling More of a Race Day Issue Than Bonking?

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If you’ve been around the running community for very long, no doubt you’ve heard how important it is to take in fuel during a long run or race.

One thing that doesn’t get talked about often is over-fueling during a race.

Yeah, it is.

And taking in too much fuel might actually be a bigger problem for more runners than not fueling enough.

Hear Me Out


That’s fine, but that doesn’t mean that I’ve completely missed the mark on this one.

Now, one thing that I’m not saying is that no one needs to fuel during a long run.

I might be saying that no one needs to fuel during a 5k, but that’s another discussion for another day.

Look, having a fueling strategy that works for you can be key to finishing a race strong, especially as the race distance increases.

But this isn’t one of those situations where if some is good, more is better.

How Likely are You to Bonk, Really?

A common fear of runners on race day is hitting the dreaded wall.

Hitting the wall, or bonking, is commonly defined as running out, or at least running dangerously low, on muscle glycogen.

And if you’re not aware, glycogen is the primary fuel that our muscles use during periods of high-intensity exercise.

Like on race day.

So the longer your race, the more likely you are to bonk then, right?

Don't Think You Need a Running Coach?

Not really.

The two keys to burning through your glycogen, and ultimately bonking, are intensity and duration.

And you simply can’t maintain maximal running intensity indefinitely.

Can you go pretty hard for a while? Sure.

And can you burn through your glycogen stores going pretty hard for long enough? Yeah.

But do most non-elite runners go hard enough long enough on race day to where bonking becomes a serious concern?

I’m not saying that bonking can’t happen to any of us, because it can.

But I’m not sure the odds are as high as some might have you believe.

What I am saying, however, is that an excess of fuel is more likely to wreck your race than not fueling enough.

How so?

The Overfueling Scenario

I’ve heard some version of this story more often than I can count.

Maybe you’ve told your own version of this story once or twice too.

Things started off really well. I felt good, the pace felt doable, and the miles were just smoothly sailing by.

Everything was on point. I took in a gel every 3 miles, a hit of water at every aid station, and I hit the half way mark right on time.

As I was approaching mile 18, I took in another gel. After that, I kind of felt a little nauseous but I just kept going. But things got worse instead of better, so I tried taking another gel to see if that would help.

It didn’t.

I struggled to the finish. The nausea just got and I couldn’t eat or drink anything the rest of the way.

Classic case of over-fueling.

It’s race day, and we are so worried about bonking that we overcompensate and end up sabotaging our race from the other end of the spectrum.

And it sucks just as bad.

Less is More

So how do we avoid over-fueling on race day?

Simple, at least in theory, fuel as little as possible.

But this is where the theoretically simple becomes more than a little bit complicated.

Because how do you know in the moment what your minimal required fueling needs actually are?


But that’s ok.

In case you haven’t figured this out yet, our bodies are absolutely incredible machines.

Thankfully, there is a pretty wide gap between bonking the extremes of over-fueling and under-fueling on race day.

As long as you’re somewhere between those extremes? Odds are, you’re good to go.

So how do give yourself your best chance of staying comfortably in the middle of the two ends of the spectrum?

  • Remember that you probably have at least 90 minutes of stored glycogen in your body, so unless you’re going really hard for more than 90 minutes you may not need any fuel at all. And if you’re running easy? You can probably go a good bit longer than 90 minutes without fuel because your body is burning body fat in addition to glycogen to fuel your run. Even if you’re not fully fat-adapted.
  • Depending on the fuel source, it is going to take ~30 minutes for what you take in to be digested enough to be utilized. So give the fuel that you do ingest time to actually be digested before you add more to your stomach.
  • Get too much fuel in your stomach than what your body can process while running and your body decides to solve the problem by voiding your stomach. Cue the nausea. Not for nothing, this is why sometimes throwing up mid-race actually helps you feel better.
  • The harder you’re working, the longer the digestion process takes. So spreading out your fueling windows might be the right call here. As an example, instead of fueling every 5 miles like you do in training, you might fuel every hour because your race pace/effort is higher.

This Isn’t an Easy Nut to Crack

I wish that avoiding over-fueling, but making sure you’re fueled sufficiently, was an easy problem to solve.

Clearly, it’s not.


This is yet another area of running where avoiding fueling dogma is important.

Perfect race day fueling is a constantly moving target.

Thankfully, for most of us, perfect precision isn’t required.

Your margin for error with fueling enough, but not too much, is pretty big.

Aim for close enough with your fueling, and odds are you’ll avoid both the bonk and the nausea on race day.

Stop worrying about bonking. Make sure you're not over-fueling on race day instead. #runchat Click To Tweet

What is Your Race Day Fueling Strategy?

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