Mountain Biking - Why did i bonk

Please help i normally ride 30 -40 miles on the road and dont bonk why did i bonk when i only rode 5 trail miles . my pre ride prep is about the same nothing has changes and i bonked hard . whats up with that ? Please help.




Rob

Originally posted by NCFR69
Please help i normally ride 30 -40 miles on the road and dont bonk why did i bonk when i only rode 5 trail miles . my pre ride prep is about the same nothing has changes and i bonked hard . whats up with that ? Please help.

Some trails require you to go anaerobic more often. How hard were the trails? There's one trail here that's only a 15 mile loop that's much harder on my body than doing a fast century. It starts out with 3 miles of singletrack climbing with a 2,000 foot elevation gain. |8^) And no... I've never made it all the way without some walking.

Forgot the Red Bull......darn!

I think trails are harder. Take the three main ones I ride.

1 - Lost lake loop -> Lower panarama - I can go for hours on this and will generally do 30k when looped around and with the trip there

2 - single track and fireroads (man we have some rough fireroads) I am usually limited to 20k (I don't bonk but my body starts to ache)

3 - Forplay (my fav single track) only 15k the average rider wouldn't make it 4k. it is a loop that goes straight up for 7.5k and then straight back down. In this 15k I am a dead man. I hurt and the so tired that the downhill section (coming back) is hard work to just stay upright.

Either way mtb is more physically demanding than road bikes. Maybe not aerobically but definately physically.

Not to mention that the bikes are considerably heavier and those big knobbly tyres, make things that much harder.

CHEERS.

Mark

Please help i normally ride 30 -40 miles on the road and dont bonk why did i bonk when i only rode 5 trail miles . my pre ride prep is about the same nothing has changes and i bonked hard . whats up with that ? Please help.

A humourous linguistic slant. In the UK, to 'bonk' is to have a sex.:)

To rephrase your post then for the UK readers:

"Please help i normally ride 30 -40 miles on the road and dont have sex why did i have sex when i only rode 5 trail miles . my pre ride prep is about the same nothing has changes and i shagged hard . whats up with that ? Please help."

Nothing wrong with that, pal! Who was she?

Originally posted by NCFR69
Please help i normally ride 30 -40 miles on the road and dont bonk why did i bonk when i only rode 5 trail miles . my pre ride prep is about the same nothing has changes and i bonked hard . whats up with that ? Please help.

Rob

Perhaps it was just a bad day. However, as mentioned, off-road cycling can be much more physically demanding than on-road riding. You are using your entire body when you ride single-track, so you are demanding a lot more from your cardio system. Also, as mentioned, you are going anaerobic more, which tears through calories @ a rate of about 5-times that of aerobic exercise.

Add all this up, and you may have your answer.

Also, as mentioned, you are going anaerobic more, which tears through calories @ a rate of about 5-times that of aerobic exercise.

Anaerobic is a 'killer'. I inject insulin. I went down to the gym today. I ate my usual lunch, but took a little more insulin than I normally do and my downfall? My workout was far more strenuous (anaerobic) than usual. Exercise boosts insulin sensitivity and accelerates the uptake of glucose. Result. I started to go into the first phase of hypoglycaemic coma. Nothing that a boost of glucose could not correct, but I had none with me at the time and it was race against time getting back to the office.

Point I'm making is that (a) I will never be caught out like that again, (b) everyone should consider taking some fast acting carbs/glucose when you go riding. It might just have fixed the 'bonk' before it took over.

What up, NCFR69

I'll try to lay out the physiology of what may have happened...

One measurement of how hard the body is working is "%VO2 max." Oxygen consumption (VO2) is a decent proxy for energy consumption. Thus %VO2 max is essentially the fraction of your maximum energy output.
Road biking (unless we're talking Tour mtn stages) usally has riders working at around 65%. Mtb'ing tends to make you work at around 80%.
The relationship between fuel use (ATP, blood glucose, muscle glycogen) and VO2/energy-output is not linear, it is exponential. That is to say in order to work at a 15% higher %VO2 max requires much more than a 15% increase in fuel.

I don't think increased fuel consumption completely explains why you bonked so hard, so soon. Is it possible that you were low on fuel, too? That can happen basically in several ways:

#1 - low serum/blood glucose.
Blood glucose and intramuscular fatty acid metabolism supplement your main stash of fuel - muscle glycogen. Once you run out of muscle glycogen, your muscles cannot continue high effort acitivities like cycling. If, for example, you eat a large meal right before cycling, you will get an insulin surge. Insulin lowers you blood glucose by encouraging ALL cells to increase their glucose uptake. As a result your muscles rely more heavily on native glycogen, consuming it at a faster rate. To avoid this phenomenon you must eat your big meals ~4 hours before riding, AND you must keep replenishing blood glucose levels by eat frequent carbo-snacks (the fig newton is best snack for the job)

#2 - low muscle glycogen.
Did you flog your legs the day before the ride and forget to restock muscle glycogen? Restocking muscle glycogen is most effectively done by eating a lot of carbs within 1hr (some say within 30 min., some say within 2hrs) of exercising. Try not to puke. After this critical period, refueling is slow business.

#3 - Dehydration.
I forget the physiology behind this one, but basically if you lose blood volume through dehydration, then it is harder for blood to penetrate deep into muscle tissue and perform its crucial fuel/waste exchange function. Also, H20 is needed in the metabolic process that turns glucose into ATP - the body's universal fuel medium.

#4 - Hypoxia/low tissue oxygen
Carbon monoxide inhalation? Do you smoke? Forget the breathe-right strips? You need oxygen alongside water to generate ATP in the most efficient manner. Anaerobic metabolism (no O2 required to generate ATP from glucose) is about 5% as effective as Aerobic metabolism (ATP production using O2). This is why all activity stops when you go totally anaerobic. This is why Lance has enormous mutant heart and lungs.

I'm sure there are other factors, but those are the main ones...besides I have to get back to studying now.

So to prevent bonking
- No big meals right before the ride
- Stay hydrated
- Snack frequently (I'd recommend twice as often mtb'ing as you would road biking)
- Post-ride refuel

Peace brothers
BK

By the way the bonk/shag translation provided Bokkie was the bomb.

Why did you bonk?
simple, different type of output than what you had anticipated...

We just did the 24 hours of adrenalin,
one team member was a die hard roadie, never, I mean never has ridden a mountain bike, he is in fantastic shape, regularly does a century and a half, ever other weekend.

after his first lap, 22km, he said he felt like he had just gone 100km.
its a very different kind of output. I have to work on the road to maintain a heartrate of 165, at 25km/h and Im not in as good shape as most. (riding a Mountain bike, middle ring at 90 - 100 rpm)

on the trail i have to try and conserve myself to keep my heart rate below 185.

The demands on your upper body for more technical riding requre you to work that much harder, to go the distance and as Buddah Knuckle said, hydrate, I find I drink a lot of water... I mean a lot 2l in one and a half hour lap. This helps flush out the muscles fo the toxic build up. (adp?)

Bokkie, love your translation!! :)

Buddha knuckle. Well done on a good reply. Some of your answers were well explained. But I need to add a few things as well:

1. Pyruvic acid is used during both aerobic and anaerobic processes. It is the interface between glycogen and the conversion into ATP. After strenuous excercise, lactic acid is converted back into glycogen through the reaction with pyruvic acid. There is some anecdotal evidence, that taking anything that enhances pyruvic acid, can facilitate glycogen conversion, but I've also read that you can have too much of it as well. I think the important point is to maintain homeostasis rather than unbalance it one way or the other.

2. A minor correction, not a criticism is that insulin only affects the transfer of glucose through the cell plasma to the mitochondria using specific glucose transporters. There's about 6 or 8 them in the body. Insulin promotes glucose transfer in cell that use glucose transporter 4 (GLUT-4). That accounts for a large % of cells. The brain does not depend on insulin, it takes it's glucose (roughly 100g daily) directly from the blood. The beta cells in the pancrease get their glucose through GLUT-2 transporters. I suppose that's a sort of failsafe, as otherwise, insulin would need insulin to produce insulin. Isn't the body absolutely amazing!

3. H2O is indeed a major factor in metabolic processes. It facilitates the availability of essential amino acids, enzymes, catalysts, and through renal function, helps to maintain a slightly alkaline ph, somewhere around 7.4? Anaerobic metabolism works in the presence of oxygen, but is not dependent upon oxygen.

4. Anaerobic metabolism produces something like 2 molecules of ATP and aerobic produces somewhere around 38 molecules of
ATP? I don't recall the exact figures, but in any case, yes, aerobic is more efficient but is unsuited to anaerobic demands and vice-versa. Recovery is vital during the anaerobic threshold and that's where the aerobic threshold complements it.

5. Anerobic exercise opens new metabolic pathways faster than aerobic does. Marathon runners do not need to be built like oxen. But you need the build of an ox to move a heavy weight. Getting the balance right is tricky. A solidly built lifter is not necessarily a fit lifter. A skinnier frame does not translate into fitness either.

6. There are many processes involved like you point out. Some days are just undeniably worse than others. The psychological threshold is reached much faster than the physical. There is something involved with a receptor in the brain that means we 'peak' anaerobically sometimes long before we actually get there physically.

7. All in all, it's a fascinating process, isn't it?:)

Dear Bokkie,

Thanks for straightening me out on those issues, especially the about the Glucose transporters. I opted to explain only what I understood, and so naturally that left out a lot. By the way, I agree - the body is absolutely amazing.

BK

Thanks to all who replied. Also if i ever go to the U.K. and need a shot of nookie ill remember the word bonk Thanks again to everyone.



Rob