Training & Nutrition - The Bonk

I've heard about "bonking" but have taken great care in my nutritional habits never to experience it until.... This weekend my riding partner and I went for a hard paced 30 mile ride in some good hills and during the last three miles or so I felt light headed and dizzy while my heart rate was pretty normal. Are these the tell tale signs of bonking? If not what are?

Could be a sign of not drinking enough water. If anything, this is more important than eating enough. Please tell us more.

BTW, I last got the 'bonk' last November. I was going to ban myself from posting on the old bicycleforum site as punishment, but was talked out of it.

Originally posted by jbjordin
This weekend my riding partner and I went for a hard paced 30 mile ride in some good hills and during the last three miles or so I felt light headed and dizzy while my heart rate was pretty normal. Are these the tell tale signs of bonking? If not what are?

That ain't bonking!!!! That there is dehydration sonny!!! Bonking is the build up of lactic acid in your leg muscles, and you get a distinct exuasted feeling in your legs, and then it gets hard and harder to keep going...Your legs feel like led, your HR sky-rockets,you are huffing and puffing up a killer climb...Your motivation to ride slowly but surley leaves...And then ultimate DOOOOOOOOOMM. You have to stop and take a breather. I usually try to eat a gatorade bar or powergel before any of the afore mentioned takes place.

I come from a running background and I know the importance of good hydaration. I think you are both right in your diagnosis and hadn't thought of that. That morning I had to wake up especially early (4 am) to get my fiancee to the airport and I really didn't hydrate well during the ride. I'm still new to riding and need to remind myself to drink while I ride. Any suggestions as to good hydration during a ride?

Thanks for pointing out what I grossly overlooked!

The best hydration is water, no substitute. If you do take a sports drink, dilute it half and half. Do you use water bottles or a hydration pack? I also find that being hydrated before I ride is as important as hydrating while I ride. If I'm dehydrated before I start I'll never be hydrated.

It could very well be bonking, actually. A "bonk" is hypoglycemia. This happens when your blood glocose level goes below 4.0 mmol/l [normal healthy human BG levels are in the 6.0 mmol/l range, anything about 10.0 mmol/l is generally called hyperglycemia]. This typically happens when extreme physical activity depletes the sugar in your blood [sugar=glycogen=energy]. Symptoms include dizziness, shakes, sweating, weakness, a metallic taste in your mouth, irritability and others [you may actually have all or none of these symptoms].

Hypoglycemia [a bonk] is very serious. It can cause a loss of alertnes [a problem in a paceline], loss of consciousness [a problem when riding a bike], coma or even death [as if passing out on a bike isn't bad enough]. When you feel a bonk coming on, you should do something immediately -- eat something, take a couple of destrose tablets, you may even want to stop and rest for a few minutes while you do this.

The best thing to do is to avoid the bonk in the first place. Never ride on an empty stomach, always take food on your rides and make a point of eating something every hour or so, mix some gatorade in with your water so you have a constant -- though not excessive -- supply of glucose entering your system while you ride.

Originally posted by fubar5
Bonking is the build up of lactic acid in your leg muscles, and you get a distinct exuasted feeling in your legs, and then it gets hard and harder to keep going...
Actually, no. That's lactic acidosis. It is also very common, and often occurs along hypoglycemia. The best way to avoid lactic acidosis is to hydrate. Oh... and the lactic acid doesn't actually build up in your muscles but in your bloodstream -- specifically the capillaries that run through your muscles.

FWIW:
I read somwhere that the term "Bonk" was named after a Dutch olympian named Gerd Bonk. It seems that Herr Bonk was noted for nearly passing out on training rides, usually after going flat-out for about 30 miles. Since he was a specialist in "field" contests (i.e. the throwing arts), he didn't pay much attention to pacing himself.
In the early 1970's, the term was "pulling a Bonk", which was later shortened to just "Bonking".

I agree with Chris and Fubar. Hydration!!!
A rule of thumb I use is one 24 oz water bottle per 15 miles, minimum.

Drink BEFORE, DURING, and AFTER the ride.

Lack of water also causes cramps in the legs.

A rule of thumb I use: I generally drink at least two litres of water/day in winter, at least four in summer (and sometimes as much as ten) whether I'm riding or not. Drinking a heap of water the night before the ride will help with dehydration. If it's a long ride, definitely re-fill the water bottles well before you even look like running out, and not only re-fill, but also drink heaps at this point too. Water is life.

Originally posted by velocipedio
It could very well be bonking, actually. A "bonk" is hypoglycemia. This happens when your blood glocose level goes below 4.0 mmol/l [normal healthy human BG levels are in the 6.0 mmol/l range, anything about 10.0 mmol/l is generally called hyperglycemia]. This typically happens when extreme physical activity depletes the sugar in your blood [sugar=glycogen=energy]. Symptoms include dizziness, shakes, sweating, weakness, a metallic taste in your mouth, irritability and others [you may actually have all or none of these symptoms].




I guess I had bonk messed up. Thanks though, now I can sound even smarter when I talk to cycling people!:D

Originally posted by fubar5



I guess I had bonk messed up. Thanks though, now I can sound even smarter when I talk to cycling people!:D
Yeah... I'm just a biochemistry and endocrinology geek... :D

Originally posted by velocipedio

Yeah... I'm just a biochemistry and endocrinology geek... :D

Wow, I can't even say enddc...endorcrino...endoelgy...edcrindoligy.....gosh. ;-) Science is a very cool thing!

Originally posted by velocipedio
It could very well be bonking, actually. A "bonk" is hypoglycemia. This happens when your blood glocose level goes below 4.0 mmol/l.

i was always led to believe hypoglycemia occured when blood sugar fell below 5.0 mmol/l? does the extra 1.0 mmol/l make the difference?

cabledonut.

Originally posted by cabledonut
i was always led to believe hypoglycemia occured when blood sugar fell below 5.0 mmol/l? does the extra 1.0 mmol/l make the difference?
It can. Most healthy people will see their BG levels drop to about 4.7-5.5 mmol/l just before meals or just after a work-out. That's not NORMALLY a dangerous level. If you get that low and skip food, though... that's when you have problems.

I think the best thing on any type of longish ride is a hydration system. I tend to put off drinking when I only have water bottles, "until the next corner", or "over the hill", or just because I don't want to interrupt my cadence etc., and don't end up drinking as much as I should.

With the hydro pack, besides having more water available, it's a lot more convenient, and I tend to drink more of it, more often.

Having some type of convenient enery food along is important too, as the others have pointed out, and can save your ride.