“Hitting the wall” or “Bonking” is a term used by runners and bikers to describe glycogen depletion which leads to sudden fatigue and energy loss. In all my running, I had never experienced it – until recently.
Photo Credit: sebastien.barre
I was looking forward to the November trail race my girlfriend and I had signed up for at the China Camp Basin (she’d do a 10k and I’d do the half marathon).
Unfortunately, we suffered a brain fart and went there on Sunday rather than Saturday and missed the race. Whoops. It wasn’t all bad as we hiked the trail together for 2 hours instead and went oyster shucking at Point Reyes afterward.
Still, I was annoyed at missing the race. I had been looking forward to pushing myself, so I decided to run a fast 13 miles on my own instead. And that’s when I learned what it’s really like to hit the wall.
Getting to Empty
I went on my usual route that followed the Embarcadero along the water all the way to the Marina (the top of San Francisco) and back. I wasn’t feeling super rested that morning, but I was able to maintain around a 9:30-10min/mi pace which is faster than my usual long run, but slower than previous race paces.
I started getting hungry 40 minutes in but waited until the half way mark, 6.5 miles, to eat my one energy gel. As I headed back, I felt myself getting tired, but I really kept pushing hard.
“This is a race! Go all out and finish exhausted!” I told myself.
This pep talk got me through miles 7-11 but at mile 12 I started feeling really tired and hungry. I was frustrated but slowed, recognizing that I still had 2 miles to go.
The Bonk
That 12th mile took forever. I had my eyes closed for most of it (very bad idea, don’t do this) because I was so uncomfortable and just wanted to zone out completely.
When I finally made it to mile 13, I was basically shuffling. I didn’t want to walk because I knew if I did, I wouldn’t want to start up again. I was starving and it felt like the air had become thick and resisting my motions. Every step was a struggle.
Finally around 12.5 miles, I literally collapsed on my hands and knees. I couldn’t go any further. I walked the last .5 miles, just about finishing 13 miles (without the extra .1)
See my Runkeeper activity for this run.
When I got home, I stuffed my face with snacks and microwave meals (I know, the food of champions). It took a few hours of food, drink, shower and rest before I really felt myself again.
What It Means, Physiologically, to Hit the Wall
There’s a lot more science than I can touch on here but basically it appears I ran out of glycogen, which breaks down into glucose and is one of the primary forms of energy in the human body (the other is burning fat).
The more intense your activity, the more glycogen you use (compared to fat). During most long runs, I maintained a 11 min/mi pace, which is much easier on the body. During races, I would typically carbo-load, stuffing extra glycogen into my liver and muscles, and have several energy gels or drink lots of gatorade during the run.
Because I was running hard and didn’t replenish my energy sources fast enough, I ran down to nothing and crashed. Your brain uses a lot of glycogen too which might explain why I wanted to close my eyes – your mind starts working poorly when you’re low on energy, just like your muscles.
Additional Resources
I’m glad I had a chance to experience “the wall” but I don’t ever plan on doing it again. I found some resources on glycogen depletion that you might find useful as well.
- Hitting the Wall on Wikipedia
- Avoid Hitting The Wall on Runner’s World
- Hitting “The Wall” on Marathon and Beyond
Jason Shen is the co-founder of 