The bike-run bonk is a simple case of over-nourishment with a twist. The twist is that the stomach is able to tolerate a greater volume and concentration of nutrition, and is also able to empty more quickly, when an athlete is bicycling than when that same athlete is running. So what qualifies as optimal nourishment during the bike leg of a triathlon suddenly becomes over-nourishment on the run.
In addition to that unpleasant sloshy feeling (or even full-blown nausea), a secondary problem results: inadequate supply of fluid and energy to your blood and muscles, which can quickly result in a classic energy bonk. Isn't that ironic?
You crammed all that nutrition down your throat on the bike to prevent dehydration and glycogen depletion and it winds up causing these very things—in addition to gastrointestinal distress.
The way to avoid the bike-run bonk is to fuel yourself during the final 30 minutes of the bike leg in a way that anticipates the reduced capacities of your stomach on the run. Here are five specific tips to help you avoid the bike-run bonk.