What does it feel like to 'hit the wall'?

There's a scene in the 2007 romantic comedy "Run Fatboy Run" in which the main character, Dennis (played by "Star Trek's" Simon Pegg), hits the dreaded "wall" while running his first marathon.

He's out of energy yet miles from the finish line, and a hallucinatory fog quite literally places a brick wall directly in his path. Dennis proceeds to repeatedly throw himself into it, harder and harder, until finally, mercifully, he smashes through and continues on.

The term "hit the wall" is used to describe the condition of an athlete who has depleted his or her stores of glycogen in the liver and muscles, and results in a dramatic loss of energy. It's so brutal, some even think calling it a "wall" is putting it lightly. Paul Scott of Runner's World wrote a couple years back: "Marathoners used to call bonking 'hitting the wall,' but it's actually a bodily form of sedition. In some form or another, it becomes a collapse of the entire system: body and form, brains and soul."

As someone who's training for his first marathon, the threat of bonking seems very real ... and very intimidating -- although hitting the wall is not necessarily inevitable; as a very seasoned runner friend told me recently, "it doesn't happen to everyone."

Unfortunately, if it does happen to me, I suspect I'll know instantly that nothing could have been done to prepare for it. Still, in the interest of getting at least some vague idea, I recently asked real runners (i.e. friends on Facebook) to describe the sensation.

Siobhan: "It feels like your legs can't support you and they turn to jelly ... the only thing that keeps you going is the cheering crowd and knowing that the finish line is just a few miles away."

OK, so basically: It hurts. But keep moving -- it's almost over. It'll all be worth it in the end.

Brian: "It's not that you can't catch your breath, it's that you feel like you can't move. The brain is mush, the body is mush, it's the single-mindedness of the finish line and stopping the suffering that keeps you going."

So basically: It hurts. But keep moving -- it's almost over. It'll all be worth it in the end.

Laurena: "All I remember is at Mile 23 the cheering started to piss me off, there was a nasty smell of beer in the air and I started yelling at the poor friend of mine who jumped on the course to run a mile with me. Seriously, when I'm trying to finish a marathon don't ask me, 'So ... New York next?' Then I had a rush of adrenaline and got back on the ball to finish strong."

Basically: It hurts. But keep moving -- it's almost over. It'll all be worth it in the end.

Stacey: "The only time I've ever hit the wall was on the bike at the Over the Mountain tri. I felt like I couldn't move, I was talking myself out of even finishing the bike. My head was nodding and I felt very foggy. Carrying the bike on my back sounded like more fun than riding it if I had to climb one more mountain. I told myself that I was just going to give up, be done, not even do the run. This feeling lasted about 20 minutes (a lifetime at the moment it was happening) and once I was over the last hardest hill, I regained composure and got the excitement back again and couldn't wait for the run and to see that finish line. I fell to the ground after I crossed the finish line and cried -- because I beat my target goal."

It hurts. But keep moving -- it's almost over. It'll all be worth it in the end.

Anyway, what I took away from these responses is this: I might be able to crudely replicate the feeling of hitting the wall, perhaps by throwing myself against the nearest brick rowhouse over and over and over again. But the truth is, it's probably best just not to let the wall worry me, to not obsess about it.

If it happens, it happens. It'll hurt, without a doubt. But if I keep moving? It'll all be worth it in the end.