Cycling UK Forum

Vorpal wrote:Well, in the situation described it's most likely rest &/or psychological.

I would think that for most people, it takes 20 or 30 minutes to convert simple carbohydrates (i.e. sugar) into useable energy.

~20 years or more ago I read of a study of this. The burden of it was that eating simple carbs caused a rise in blood sugar far more quickly than could be explained by absorption rate. The authors speculated that sweetness in the mouth meant that it was safe to release a "last reserve" that otherwise would have been kept back. It would be interesting - and maybe dangerous - to repeat the experiment with artificial sweeteners.

A similar thing happens with camels that have gone without water for a few days. Almost as soon as they drink they will pee, long before the water could possibly get through to their bladders.

There's a limerick in that somewhere...

This makes sense. When I’ve had “hunger knock” (assuming that’s what it usually is), the effect disappears very quickly after eating sugary food i.e. almost instantly. I’ve often wondered if there is a mechanism of this sort.

Sweep wrote:As above, once bonked, get some sugar in me quickly.

It's only happened to me a couple of times and not for a long while, basically because, forewarned, on a long ride I regularly snack - homemade cycle snack (mix of fast and slow release stuff) and, yes, those Lidl wine gums.

First signs of impending bonk as I recall were maybe more than expected sweating, certain slowness in reacting to things (hence it can be dangerous) and, as I looked at the speedo, the clear realisation that I was going far slower than I should be on a fairly flat road. I suppose the fact that I had to look at an electronic device to really be "told" that something was up shows how befuddled my mind was becoming. At that point you need to get off the bike for all sorts of reasons.

Another sign according to a doc who used to come on a lot of my rides is folk getting angry, unreasonable, argumentative. He reckoned that the reason there was often a lot of trouble in A&E of a saturday night was not primarily because of alcohol but because of low blood sugar. This topic came up discussing, after the event, a particularly tough ride of mine he'd been on (subsequently billed as "the hell of ......." so that folk couldn't say they weren't warned) where I as the ride leader had a fair amount of aggresion thrown at me in the latter stages - before the entire field abandoned it

maybe you should get round to that ride with me al - if the bonk approaches I promise to dangle a wine gum in front of you.

all the best

Hi Sweep, I've got type I diabetes so am forced to know a bit more about sugar metabolism than most folks. Injecting insulin can create all the effects of bonking at any time with no need for exercise [emoji3]

Agree with your friend's suggestions about aggression and sugar and Saturday nights -
low blood glucose makes people stupid and aggressive, and alcohol reduces the ability of the liver to release glucose from storage so if you're cold and/or hungry it's easy for bg levels to drop.

A couple of relevant points for the original question :
1. Snickers bars aren't that great at raising or replacing blood sugars. The fats in the bar slow absorption. Much better to use pure glucose or a sugary drink if you need sugar in a hurry.
2. Unless you've already used up all your reserves, the act of going uphill will stress your muscles, causing them to release cortisol; in response your liver will immediately break down glycogen and release extra glucose into the bloodstream. No need to wait for a Snickers bar. You need to eat to replace the reserves, but that can happen later on,and is why people are generally starving after a hard ride ends if they haven't kept themselves topped up.

Because of point 2, I never eat before a hill and check how high my bg levels are at the top, sometimes taking more insulin to avoid dehydrating and cramping.

I'm a trendy consumer. Just look at my Nexus 6P using hovercraft full of eels.

Samuel D wrote:Glucose is absorbed quickly in my case. I believe I start to feel its effects in five minutes.

It likely varies from person to person. I can eat and digest a ham sandwich while riding briskly, to the surprise of some of my companions.

On the other hand, when I bonk it is a serious matter. The last time that happened it took me two hours from eating to find the strength to continue my ride. Meanwhile I felt horrendous: light-headed, heavy-legged, and weak as a kitten. For the first half hour I had to sit beside the road with my head between my knees.

You should have porridge for breakfast, slow-release carbohydrates
And heed Velocio(Paul de Vivie): eat before you get thirsty, drink before you get hungry

Was it wrong for me to have a fish supper every 30 miles of a 100 mile cycle? ( was only two but they were enormous fish suppers ) then a packet of sandwiches for the last 20 miles. + some chocolate after the sandwiches.

Cowsham wrote: ↑15 Apr 2024, 6:14pm Was it wrong for me to have a fish supper every 30 miles of a 100 mile cycle? ( was only two but they were enormous fish suppers ) then a packet of sandwiches for the last 20 miles. + some chocolate after the sandwiches.

Almost certainly. Protein and fat takes many hours to digest, and if you are pedalling hard body resources will switch from digestion to powering your muscles, meaning it takes even longer.

Of course, if you were pedalling easily then the first fish supper would probably be beneficial to the later stages of your 100 mile cycle ride

Those really interested in their metabolism could do a lot worse than consider the Zoe app (the company's website here).

Cowsham wrote: ↑15 Apr 2024, 6:14pm Was it wrong for me to have a fish supper every 30 miles of a 100 mile cycle? ( was only two but they were enormous fish suppers ) then a packet of sandwiches for the last 20 miles. + some chocolate after the sandwiches.

During audax rides I have always envied those who could consume a large meal and then continue cycling at a good pace.
If I tried the same the fish supper would be regurgitated after a few miles.
During a ride I eat small amounts when I feel the need.
I dreaded controls in "greasy thumb" cafes - it was difficult to find something that I could easily digest.

I think I must have a very different metabolism to most, I don't think I have ever bonked, Have worn myself down to a frazzle on many occasions, but I just feel tired and get slower and slower - I can always keep going. My wife is quite different, she will complain of feeling a bit light headed if she hasn't eaten for 3 or 4 hours, she does not cycle but if she did I reckon she would 'bonk'

Even at the moment where I am trying to loose a few pounds, I am fasting twice a week for 24 hours at a time, I don't feel I have any less energy on the days when fasting, don't even feel hungry (I can verge on a psychological break down around meal times in watching my wife eat and all those wonderful smells of cooking), but that is just an overwhelming desire to eat and not hunger. Hunger is very different and something I guess many people have never experienced, takes days to get there and its very different to just wanting to eat. Try it sometime its an interesting experience

ANTONISH wrote: ↑16 Apr 2024, 9:18am

Cowsham wrote: ↑15 Apr 2024, 6:14pm
Was it wrong for me to have a fish supper every 30 miles of a 100 mile cycle? ( was only two but they were enormous fish suppers ) then a packet of sandwiches for the last 20 miles. + some chocolate after the sandwiches.

During audax rides I have always envied those who could consume a large meal and then continue cycling at a good pace.
If I tried the same the fish supper would be regurgitated after a few miles.
During a ride I eat small amounts when I feel the need.
I dreaded controls in "greasy thumb" cafes - it was difficult to find something that I could easily digest.

The first 400K I did I was 4lb heavier after the event. The food was excellent
I remember on a 300K in Northumberland being unable to resist a fish supper in Wooler. They sat heavily undigested in my stomach for the rest of the ride back to North Shields. Lesson learnt never to be repeated on an Audax.

Doesn't it all depend upon how fast you're going and your muscle fibre type? Plus there's another stopping mechanism - hitting your lactate threshold at which point you'll be in pain and will need to stop to let lactates disperse.

People becoming angry and aggressive with poor decision making becoming apparent is an indicator of a diabetic hypoglycæmic event in first aid, bonking is a similar event.

The OP is correct that ATP is the energy supply used by muscles, but if you look at the numbers, you have enough ATP and PCR (which can be instantly converted to ATP) to go for 15 secs. Then you're in to stored glycogen which you're going to convert into ATP either anaerobically or aerobically depending on how fast you're working. Aerobic is slower but gets the most energy, Anaerobic is faster, gets less energy from the food (storing the excess as lactate which can be used later). Aerobic vs Anaerobic seems to differ with muscle cell type, how old you are.

After a few hours you then switch to aerobic conversion of fats, at which point you're going to be going relatively slowly.

Quite difficult to make sweeping generalisations about as some of it is genetic, some depends on which sports you did as a kid, some on your current training regime. I know my problem with hills is that I hit my lactate threshold quite quickly if I get the gears wrong - and will start panting to try and clear lactate, which boosts heart rate which increases lactate generation etc. etc.

Cyril Haearn wrote: ↑26 Apr 2018, 5:11am You should have porridge for breakfast, slow-release carbohydrates

Depends on what you're doing. You probably can't replenish carbs fast enough if you're anaerobically exercising. Probably better to eat pasta for a few nights before if you need a big energy reserve building up.

Audax67 wrote: ↑25 Apr 2018, 2:19pm ~20 years or more ago I read of a study of this. The burden of it was that eating simple carbs caused a rise in blood sugar far more quickly than could be explained by absorption rate. The authors speculated that sweetness in the mouth meant that it was safe to release a "last reserve" that otherwise would have been kept back. It would be interesting - and maybe dangerous - to repeat the experiment with artificial sweeteners.

I was told something similar about artificial sweeteners. Was roundly ridiculed when I mentioned it on here.

There's a great book from MIT on the science of cycling. It covers everything from human power generation, to calculating what gearing and braking is required for a new bike build, calculating battery requirements for EPAC, reducing drag and rolling resistance etc. https://www.google.co.uk/books/edition/ ... frontcover

nirakaro wrote: ↑19 Jun 2014, 1:53pm A question for any nutritionists out there:
Sometimes I look up at a hill and think, I’m not going to get up that without refuelling. Stop and gobble a quick Snickers bar, and up I go.
Can my body really do its Snickers-bar>blood-sugar-level>adenosine-triphosphate-in-the-muscles magic trick that fast, or is it just a bit of wishful thinking, placebo effect, and a minute’s rest?

I think the important thing to realise is that everyone is different. The rate at which we process foods differs wildly, depending on a lot of factors. We’re just starting to understand the importance of our gut biome and how that effects all sorts of mechanisms. This article in Men’s Health magazine is worth a gander. It will be equally interesting to women, too…

simonineaston wrote: ↑15 Apr 2024, 6:39pmThose really interested in their metabolism could do a lot worse than consider the Zoe app (the company's website here).

What data does it provide, and how?

ANTONISH wrote: ↑16 Apr 2024, 9:18amDuring a ride I eat small amounts when I feel the need.

I recall an article in the CTC mag, they were reprinting, or quoting from, an article from the days of penny farthings: "Drink before you feel thirsty, eat before you feel hungry, and ride well within yourself for the first hour".

axel_knutt wrote: ↑16 Apr 2024, 11:20am

simonineaston wrote: ↑15 Apr 2024, 6:39pmThose really interested in their metabolism could do a lot worse than consider the Zoe app (the company's website here).

What data does it provide?

See their FAQs page here.

simonineaston wrote: ↑16 Apr 2024, 11:45am

axel_knutt wrote: ↑16 Apr 2024, 11:20am

simonineaston wrote: ↑15 Apr 2024, 6:39pmThose really interested in their metabolism could do a lot worse than consider the Zoe app (the company's website here).

What data does it provide?

See their FAQs page here.

I didn't find any mention of it measuring metabolic rate.