I’ve gone through a few bonks in my life (one very bad) so I know what they feel like. I’m wondering, however, what happens chemically inside the body during one of these. Obviously, the body runs out of its preferred fuel - complex sugars, carbs, etc - but what happens when it runs out and what compensation mechanisms kick in that result in that dizzy, depleted feeling?
Any good links or information would be appreciated.
From what I understand, a true bonk is when your brain runs low on glucose, hence the dizziness. I believe many people blow up/get cooked and consider that a bonk but, IMO, a true bonk doesn’t happen that often. I could be wrong though!
Bonk is usually assocaited with running out of fuel, but I do not believe it is they only way to actually bonk…
If I am not mistaken, a bonk starts to take place when you body (your brain) feels whatever your are doing become “dangerous” (i.e. for example you are starting to run our of fuel, or you are running in extrem heat and are not use to it). I am not sure what exactly takes place chemically, but your brain starts to shut down your body (or go into “energy saving mode” first)… Similar to the “gas light” in in your car to let you know you better hit the pump soon…
That being said, I did not stay @ an Holiday Inn Express nor I am a doctor/physiologist/astronaut…
Cheers,
Fred.
Hopefully someone who actually knows the answer will respond…but here’s my understanding.
Two things. First the body burns 3 fuels, fat , protein, and carbs. I also believe that carbs are required in the process of burning fat and protein makes up a very small portion of ones fuel 10% or less even under very extreme situations, starvation.
If you run out of carbs you run out of not only the preferred fuel but also the ability to convert fat to fuel. Thus you are rely nearly 100% on protein and some other “safety measures”.
Since your brain and some other major organs use only carbs for fuel you are basically starving your brain, that’s bad. In minor situations you get dizzy, worse hallucinations, then finally unconsciousness…then you die in very severe cases. In most cases the “Bonk” serves a limiter to make you stop before you get to the point of death.
This bonk is entirely different than what most people call a bonk, from fatigue, slowing down etc. Many times people become dehydrated and call it a bonk, which it technically is not.
Most of the info I got above is from Noakes *Lore of Running, *but is from memory so it probably means I completely butchered it and it’s wrong.
~Matt
Actually, the midi-chloridians in your cells shut down cutting you off from the Force.
Honest!
Damn it! I knew I’d get that wrong…yeh it’s all about “The force”.
~Matt
That book definitely explains it well. You just have to read 300 pages to understand it 
jaretj
Yeah, I finally learned last year what a real bonk is like. It’s not just getting tired as many people seem to think. I was on my bike and I just wanted to lie down by the side of the road and sleep. (I guess that was the self-defense mechanism.)
So doing a long dist bike ride, nice light breakfast earlier, taking gels and hydration is kept up. Towards the end of a rather warm and moist summer day ride, I get spacey, kind of zoned out all of a sudden, I’m kind of feeling too much stimulation, very drained feeling. Aero position gets extremely uncomfortable and swerving seems unavoidable, and I feel like I just want to go 10 miles an hour or get off. A slight hunger in my belly, but mostly just nothing more to give. What would you call that? Bonk, Blow up, or just a good workout?
For me, when it’s a true bonk I’ll sure as hell know it…there will be no second-guessing what is going on.
I’ve had one what I would call one bonk - near the end of a long hot training ride where I know I didn’t come close to drinking or eating enough. Stopped at a friend’s before finishing the last 20 km home when it felt like a wave of dizzy like sensations ran through my head, slight ringing in my ears, I could feel my forehead get really cold and even my vision became a little tinted. Sat down for about ten minutes and drank more nutrition, then finished the ride home. It was probably the longest 20 km I’ve ever done though.
Martin
A stroke?
Honestly hard to tell. I’ve had similar feelings while simply being dehydrated. A good way to tell if it’s dehydration is to lay down and see if you feel better. If you’re having a hungry or queezy feeling laying down will make it go away if you’re dehydrated.
My only experience I had with “Bonking” was somewhat a combo bonk/dehydration. No breakfast, ride that was supposed to be an “Easy” 35 miles turned into a harder and much hillier, 65+ mile ride. I had one bottle of gatoraide, normal version and a couple bottles of water…that’s it. No Gel, no food nothing.
About 5-10 miles from getting back it was like a switched flipped. Legs went bye-bye and then shortly there after head went fuzzy. Zero ability to concentrate and the occasional flash of weirdness in ones eyes. Not quite pink elephants but more of a “Ahhh WTF was that?” I ended up stopping and resting for a while then got back on the bike. Luckily it was mostly downhill home. I managed to get back and was in serious hurting status. Legs actually felt fine but simply weren’t responding. After getting back to the car I down many ounces of Gatoraide and withing 15-20 minutes the cloudy head, dead legs everything went away. Felt fine and thought about going back out.
Whenever I’ve had any other type of crash, fatigue, over doing etc. The recovery is longer term and I usually just wanna sleep no matter what I do. In this case after getting some calories and fluids in me I felt fine.
~Matt
Bonking is a chemical process wherein your blood-sugar is converted to hopelessness and despair
.
that is great - I’m writing that down. Your quote?
Thank you. That is indeed my quote.
I’ve gone through a few bonks in my life (one very bad) so I know what they feel like. I’m wondering, however, what happens chemically inside the body during one of these. Obviously, the body runs out of its preferred fuel - complex sugars, carbs, etc - but what happens when it runs out and what compensation mechanisms kick in that result in that dizzy, depleted feeling?
Any good links or information would be appreciated.
I believe there are several kinds of bonks, including the out of fuel bonk, the low water bonk, the too much water bonk, the out of sodium bonk, the “i didn’t train my muscles for all of this bonk”, and some combination of any or all of the above, etc. To which kind of bonk were you referring?
Great book…Reminds me to read it again because it is so informative.
I’ve gone through a few bonks in my life (one very bad) so I know what they feel like. I’m wondering, however, what happens chemically inside the body during one of these. Obviously, the body runs out of its preferred fuel - complex sugars, carbs, etc - but what happens when it runs out and what compensation mechanisms kick in that result in that dizzy, depleted feeling?
Any good links or information would be appreciated.
Some of the responses above are right on track. Firstly though, forget about things like ‘converting’ from using carbs to fat.
The ‘genuine’ bonk occurs when your liver is empty (or close to) of glycogen. The primary role for the liver glycogen store is to maintain blood glucose. The only other substantial store of glycogen, your muscles can only use glycogen to supply themselves (ie once glucose enters a muscle cell, it more-or-less cannot leave). When the liver runs low, blood glucose levels can begin to fall if the liver (and to a small extent kidneys) can’t make new glucose out of other ‘stuff’ fast enough to meet your exercise-induced demand.
The bonk is therefore the brain responding to loss of its glucose supply. It pretty much relies on glucose to maintain itself, and can only use other things (some ketone molecules) to a limited extent. If the liver (or an exogenous glucose supply) can keep blood glucose steady during extremely prolonged training/racing, muscle can sustain useful work rates (not really high intensity) in the face of quite low glycogen content, with muscle fuel supplied primarily through fat and a little blood glucose. On the contrary, if your muscles are well supplied with glycogen, but the liver is empty and not keeping up demand, you’ll bonk in spite of well-fed legs.
Remember: your liver (and overall fuel selection) is trainable, and this should be seriously considered in any endurance training program. As I said above, you can maintain decent work rates on fat-fuel, but you need to train it………
CLA, can you elaborate on the ‘Liver training’? Would that be intentionally depleting the Glycogen stores in the liver?
“The bonk is therefore the brain responding to loss of its glucose supply.”
This is the key component of a true bonk. Since your brain relies almost entirely on blood glucose as a fuel source, when blood glucose drops as liver glycogen is depleted (you can’t very well ingest enough carbs to maintain blood glucose levels if exercising long/hard enough) you get mental effects (e.g. dizziness, impaired thought, increased sense of effort for a given work load). Of course, by that time much of your muscle glycogen is going to be depleted too in many muscle fibers and they will be relying almost only on fat as a source of energy, which is a slow process, and that will compromise power too.