I kicked off marathon training last weekend with my longest run ever (20 miles). For my long run, I employed a foolish strategy of taking no nutrition or fluids. This was intentional. A compelling comment on the fall marathon thread on Slowtwitch had me thinking–a poster had admitted to a curious method of letting himself “bonk” on long runs during marathon training in order to become familiar with hitting the wall and to practice pushing through it. That sounded really hardcore, so I was game to try it.
I found the wall around mile 17, and it was like nothing I’ve ever felt. Bonking on the bike is mostly a fatigued, crappy feeling that develops over time–the long run bonk felt musculoskeletal, and came on instantaneously. My legs were suddenly leaden and crampy and every stride felt forced. The final three miles were as hard as the initial 17, for which I settled in at around goal M-pace +~0:10 without too much trouble (definitely very hard, but manageable).
Now I know what marathoners are talking about. I think the forced bonk was actually a valuable exercise, though I wouldn’t wish it on another. The key is to not experience this during a marathon. If you are trained properly, and if you pace properly, you shouldn’t find it on race day. Here’s hoping.