Bonking happens when you deplete your glycogen stores in your liver and muscles, which ultimately leaves you weak and unable to continue on at the same effort as you were moving at. This is why we fuel during endurance events - to prevent complete glycogen depletion. And we do that by consuming carbohydrate rich foods, such as gels, sport drinks, etc. On average, your body can store between 1500-2000 calories worth of glycogen that is spread throughout the muscles, so needless to say, you can bonk relatively easily in endurance events that last many hours (ie marathons, ultras, half ironmans, ironmans, etc), when you can burn 500+ cals/hr.
However, this is where we see the greatest misuse of the term. Bonking is NOT slowing down toward the end of a 5k or a 10k. That is what I like to call "improper pacing". You simply went out too hard for your current fitness and your body could no longer sustain that effort. Either your muscles are too fatigued, or your mind gave up wanting to deal with the pain associated with running too hard. You did not however, bonk, as you clearly have not depleted your glycogen stores in such a short effort.
So with that said, let's just talk about some basics for preventing bonking:
- Properly fuel during workouts and races - Don't go into key workouts or races on empty (unless that is the purpose of that particular workout), especially if it is a morning workout. This means you've been fasting since dinner (or that midnight snack) from the day before. Not a good way to ensure full effort from your body.
- Properly re-fuel after workouts - Make sure you replenish your glycogen stores following hard workouts (preferably within 30 minutes). 30 minutes is a general number that people give for optimal recovery following hard bouts. Typically, anything in the 90 minute range (or something shorter but very intense) is what I consider hard bouts.
- Pace according to your fitness - In longer endurance events (read: not 5/10ks), pacing is just as important, because at higher intensities, your body is working harder and using more of your glycogen stores to maintain that level of effort. Pacing according to your fitness ensures you are more efficient to handle the workload so that your body doesn't have to work harder than it already is to keep up with your effort.
- Practice race pace - This goes in line with pacing, but your body needs to know what race pace feels like in order for your to race it efficiently. Race pace will differ depending on the distance, so make sure you train according to that particular race. Practicing 1/2 marathon pacing bouts when you are training for an ultramarathon might give you a good workout, but it isn't going to help you become more efficient at race pace. You can practice this through tempo runs, specifically designed race pace runs, and in parts of your long run, especially toward the end.
Ok - I feel better now that I've got that off my chest....(sigh)...