Yesterday I ran into an old friend who completed his second Ironman triathlon this past summer. Eager to hear about his experience in person, we sat down to have a cup of coffee while we told me all about his 140.6 mile adventure. It was pretty standard at first, with tales of cold water, pacing issues, and constant doubting. When you race for 10+ hours, these things happen. But his story really got interesting when he detailed what happened to his brain on the run.

Friend: “So, I looked down at my watch on the run to see if I was hitting my pace, and I couldn’t see the numbers.”

Me: “Oh, your watch reset? That stinks after all that pacing prep.”

Friend: “No, I mean, there were numbers there. The watch was fine. It’s just that my brain couldn’t process what it was seeing.”

Me: “So your eyes looked at the numbers, but you had no idea what the numbers meant?”

Friend: “Yeah, like that. It’s as if I had never seen a number before in my life.”

He finished the race and hung out in the medical tent for a bit until he felt well enough to stand up and move around. Overall, he was psyched about how the race went, and his smile was huge as he recounted every detail of the race for me. But the experience of having his brain feel like scrambled eggs freaked him out a little, he disclosed. I decided to go home and do a little research about how this could happen.

It’s About Glycogen, Silly!

 
My friend had scrambled eggs for brains most likely because his brain glycogen was severely depleted. Glycogen is stored in the muscles, liver, and brain. During endurance exercise, glycogen is used to fuel respiration and movement. Glycogen provides energy. Even though athletes consume simple sugars during the race to replace depleting glycogen, energy stores can still deplete faster than they can refill the tank. The muscles store about 2 hours of energy in the form of glycogen before it needs to pull glycogen from other sources.

This is your brain on . . .

 
Studies have shown that prolonged exercise, like Ironman racing, can deplete glycogen in the brain too, as the body pulls energy from other sources. My friend felt like he had literally lost his mind because of a potent combination of increased monoamines and decreased circulating blood sugar and decreased brain glycogen. Monoamines are neurotransmitters in the brain like dopamine for example. Luckily, this process is reversed as the body recovers from the prolonged exercise session.

Have you ever had brain fog during exercise? What happened?

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