There are two slang terms that get thrown around among distance athletes, bonking and hitting the wall. I hear people using these terms and quite often confusing them or mixing them up.
So what happens when you "Bonk" and is it always bad when you Bonk?
When we exercise there are 3 energy systems that we can use to get energy; aerobic system, anaerobic system and phosphagen system (will be discussed in a later post). It's not important to understand those systems completely. It is important to know that each system relies on glycogen as a fuel source, however the reliance on glycogen differs between each system. The aerobic system for example is efficient at using fat too as a fuel source, while the anaerobic system relies on glycogen only and can not use fat as a fuel source. It is also important to know that all systems are in use all of the time when you are running or cycling but again the reliance on each system will vary massively depending on your training set.
As we exercise the glycogen stores become depleted. In the average runner these stores last about 90mins give or take 30mins either side. If you are a real beginner carrying excess weight you might get about 60mins from your glycogen stores, whereas if you have been training consistently for a few years and can hold a good pace while racing you might get 120mins from you glycogen stores. But for the average Joe out there lets say 90mins.
During exercise we are smashing up these glycogen chains (sugars) and oxygen to release energy (ATP) used by our muscles and nerves. The power stations (mitochondria) in out muscle cells can use glycogen and/or fat as a fuel source. However our nerve cells can only use glycogen for fuel. So when our glycogen stores start to get really low our muscles can rely on fat burning and are quite happy to continue. Our nerve cells begin to run low on fuel. Physically we feel quite good at this point but mentally we are a mess. Or to put it in runners terms "Bonking". Our thoughts become confused and we get very agitated, our form will be messy because we lose fine control of our muscles. This poor form requires more energy, plummeting energy stores even further, a negative feedback system for the Bonk.
Bonking means the brain is running out of fuel and is at the early stages of shutting down. Anybody who has fainted during a marathon or triathlon can probably attribute it to the fact that their reticular formation (the part of the brain that keeps you awake) ran out of glycogen.
Bonking is hugely responsible for bike accidents. How often do you hear of some body in your club falling off? I bet if you investigate the crash took place more than one hour into the ride. Bunch sprints in cycling races are notorious for crashes, partly due to the explosion of speed, riders fighting for road space and coupled with the rider in the middle of the action not fully alert due to the BONK!
What all this means is that at about 90mins into a Race you are going to Bonk unless you take measure to combat this. Racing is usually performed in Zone 3 of your heart rate. At this pace you are working aerobically which means the muscles are burning glycogen and fat. The fat burning will delay the bonk by not letting the glycogen stores become completely depleted as quick. However the nervous system is only able to burn glycogen so no matter how fit you are the Bonk is always coming.The more training you do the better you are at getting into the fat burning zone. It is so important to consume some sort of carbohydrate food source if you are exercising over 60mins. Otherwise at some point your form or technique will suffer as a result of an undernourished nervous system.
Note: this blog is not intended to coach or tell you what to do, my goal is to explain this stuff and make it understandable. However I would like to stress that I do not recommend using sports drinks and energy gels to combat the bonk while training. There are other measures that are more ideal which won't screw up your gut or send you on an insulin roller coaster.
Simple carb intake will cause a massive injection of insulin from the pancreas. The insulin will tell every cell (including muscle cells) in the body to burn glycogen and stop burning fat. Within seconds the energy drinks and gels will be utilised and the nervous system will be left wanting. Consumption of a more complex type of carbohydrate snack is always going to have a better effect. It will take longer to break down, so it is a slower release of energy. There is a gradual insulin release from the pancreas and a far better performance from the athlete.
I think it's safe to say that the vast majority of the time it's a bad idea to Bonk. Not only do you become agitated, confused and emotional, your form becomes really poor and the muscle are in a position to start breaking down proteins to fuel movement, which is always a bad idea.
Their may be some benefit to experiencing this once in preparation for a race. If you know what the Bonk feels like from a training experience you can notice the symptoms developing during a race, this can enable you to know when to refuel and what type of fuel you should be taking at a particular point of a race. It's obviously not a good idea to Bonk every time you workout but there can be some benefit to a once off experience.
Recap: bonking is when the nervous system has not got sufficient fuel to perform its tasks and the brain begins to malfunction.