I finally figured out what caused the hiccups at the Chicago Marathon.
It turns out that a full stomach can put pressure on the diaphragm, and the competing pressures on said diaphragm during a long moderately intense run like the marathon can finally cause the relevant muscles and organs to effectively cramp, spasm and whatever else organs do once they finally run out of gas.
It turns out I fueled *too* well during the early portion of the race. I had taken in over 16 oz of protein and carbohydrate within the first hour. Combined with with the natural slowing of digestion as you get into a longer run of any substantial intensity, I had suddenly maxed out the tank before reaching the halfway point. The pressure on my diaphragm finally caused it to give up around miles 12-14, and there wasn’t much I could do from there.
Preventing that next time around is fairly easy: Just make sure not to take in so much fuel.
Of course, that presents another, more common marathon problem: If I don’t take in enough overall, I bonk during the final 10K. And of course your stomach’s digestion slows either way as you proceed. So rationing harder only means fuel taken in later doesn’t get digested in time to be used. It was a key reason I was working hard to fuel in the early stages of Chicago.
I don’t have a firm answer yet, beyond going unpleasantly slow and letting fat-burn catch up enough to fuel the entire race. Ultrarunners succesffully find a middle ground, and I imagine the answer lies somewhere within how they fuel for their much-longer races.
This is a research project that will fit into the rest of my training.