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How many calories per hour needed to prevent bonking?(17 posts)

How many calories per hour needed to prevent bonking?OffTheBack
Oct 15, 2003 12:11 PM
Had a nasty bonk at the end of my ride on Sunday, which got me to thinking: I've seen estimates that during hard riding you can burn 500 - 800 calories per hour. If you tried to replace all of those during the ride (even assuming you can ride for the first 1 1/2 hours on stored glycogen), that would be a lot of powerbars, like 1 every 20 minutes. That seems more than is necessary... but then, I sure as heck bonked on Sunday with 1 powerbar on a 3 hour ride (after breakfast). Thoughts?
It will depend...Dwayne Barry
Oct 15, 2003 12:23 PM
on how hard you are going, how fit you are, if your glycogen stores were topped-off. In general, the harder you go, the faster you're burning liver glycogen and faster you're heading toward a bonk. Also the fitter you are the greater will be your aerobic capacity which will have a glycogen sparing effect. Also the faster you go the harder it is to get calories. I think you can only absorb somewhere around 300 cal/hr at a hard race-like intensity.
300 to 400...Lon Norder
Oct 15, 2003 12:27 PM
That's about all you can process per hour. The rest comes from glycogen and fat stores.
Oct 15, 2003 12:37 PM
Believe me, I've tried to process more than 300 or so per hour, and it will not work. The bottleneck is your GI tract. Only so much will pass into the blood so fast. That amount is usually noted around 300 CHO calories per hour, and that's with large molecules and plenty of water.

Here are some of the tricks, though. The more your train for endurance, the larger portion of your energy expended is from stored fat. So, even though you may burn CHO at the same rate, you can go faster, longer because you burn more fat.

RAAM riders are on the bike about 20 hours a day for 8-12 days straight. They obviously reach a steady state between injested and burned. They report being able to use only about 300 CHO calories per hour.

Ultimately, if you cannot sustain your CHO replacement, one stark reality sets in -- slow down. That's all you can do. No one can escape the physical laws -- you cannot ride fast with no gas in the tank.

So, here's the bottom line -- if it's a long event, injest about 300 calories per hour. That's all you can do. More won't do any good, and less could lead to gradual depletion and bonking.

I think 300 is pretty optimisticcyclopathic
Oct 16, 2003 8:56 AM
and you have to train to utilize as much. Mine is ~150-200 tops, but I am only 140lbs. The actual top absorption rate will depend on many conditions like temperature, humidity, hydration, level of effort, stomach condition, type of food, etc,etc,etc.

It takes some time to figure it out. Many newbees to ultramarathon riding make mistake of going on liquid diet only w/o adequate training/testing. If something work for you on 8hr ride, it doesn't mean it still will after 20.

On PBP I carried through the ride a bag of Perpetum (I could not take it after 8hr on bike). And after the ride you should have seen how many unopened bottles of Hammer Gel went into trash people were throwing it in disgust.

Most randonneurs including me use mixed diet, combination of sustained energy, jells and solids.

This is mostly irrelevant for short 60-150mi rides. Generally you can get through the ride w/o any food and if you bonk all it takes 1-2 gels, water and 20min of slow spinning to get back on track.

what did you have the night before?ColnagoFE
Oct 15, 2003 12:50 PM
and are you on any sort of carb-restricted diet? starting with a full tank from the night before is best.
I found this calorie consumption guide....Cory
Oct 15, 2003 2:12 PM
May have been in Bicycling magazine a few years ago, before it went bad. They listed the number of calories per pound you use in one minute at a given speed, so to find total calories, you multiply your weight times the conversion factor times total minutes of riding.
I don't have time to list the whole speed range from 8 to 25mph (I can do it later if anybody's interested), but at 15mph, it says you use 0.0561 cal per pound per minute. I weigh 225; if I rode for an hour at 15mph, I'd use 757 calories. A 150-pound person riding at 20mph would use 801 per hour (.0891 x 150 x 60).
Don't know how accurate it is, but when I've kept track against my calorie intake, it correlates pretty closely with weight loss or gain. Mostly gain lately, I'm sorry to say....
Bicycling numbers notoriously high!Kerry Irons
Oct 15, 2003 4:31 PM
A 150 lb. cyclist at 20 mph is burning 600 calories per hour, not 800. Maybe 800 on a mountain bike with big knobbies and a not very fit rider. 1000 calories per hour at 25 mph. At any rate, for estimation purposes, you can burn about 200 calories an hour of fat, and at the start of a ride, you may have 1500 to 2000 calories of stored muscle glycogen. You also could easily have 500 plus calories in your stomach/intestines. Given the total stored energy at the start of a ride, in theory you would not need to supplement at all for a distance like 60 miles, but you'd be totally empty at the end. In practice, you can't really empty your tank, so at least 300-500 extra calories as an energy bar or energy drink is required to be your best over this kind of distance. Lots of research has shown this. Likewise the 300-400 calories per hour during hard riding has been demonstrated repeatedly. The bonk comes when you only have fat calories to burn, and you can only go about 12-13 mph at that rate of caloric expenditure.
Not sure what I am burning on Atkins. . .Look381i
Oct 16, 2003 8:08 AM
but I've been on its strictest regime for almost seven weeks, maintaining sub-20 gram daily intake of carbs. Daily testing strips tell me that I have been in moderate to heavy ketosis for virtually all that period.

After first two weeks of feeling a little sluggish -- close to bonk -when riding, I since have felt fine on 40-100 mile rides at averages of 17-21 mph with almost no apparent intake of carbs (breakfast of bacon and eggs, "lunch" of a small Endulge low carb bar and water). I have also lost at least 16 of my 22 pound target and at least two inches of fat around my waist.

Today I see my doctor to find out whether my blood tests demonstrate a material effect on my blood lipids, etc. in that period.
Many studies done on this subject and some interesting data...Mr Nick
Oct 15, 2003 2:31 PM
Most studies are done on male cyclists running at 85% of VO2 max. They ingest between 30-60g of CHO every 20 minutes. This has shown to increase time to fatigue by approximetly one hour. So about 300g an hour is going to be about right. Most tests had the athletes consume the CHO in liquid form. This equals about 8oz of Gatorade every 20 minutes. Also CHO should be what you are ingesting, no fat or protein.

It is also important to remember that time to fatigue is directly related to muscle glycogen. Muscle glycogen is your major fuel for the majority of the activity and it then moves to blood glucose near the end. (I have a cool graph, but no scanner) Of course blood glucose levels are kept stable by liver glycogen so it is important to have proper liver glycogen stores. Fatty acid use is also important for most riders, especially because not many people ride continuously at 85% of VO2 max. As you become more fit lipid mobilization and mucscle triglyceride use become more efficient.

The comment about eating before an event is really important. Liver glycogen stores in the morning are at half capacity because sleeping is a fasting state. During sleep your body uses the glycogen to fuel itself so it is very important to eat in the morning and replenish the liver glycogen stores. Studies show that the best results occur when you eat a high CHO meal 4 hours before an event. You can ingest CHO all the way upto the event if you want but they will not have as great of an effect.

Finally since muscle glycogen is the key ingredient in fatigue it is very important to store as much as possible. The way this is done is by eating high glycemic foods directly after an event. That means eating bagels and pasta within 2 hours of your ride. This is the time when your body is most ready to store glycogen. They have found that the high insulin levels associated with high glycemic foods cause an actual increase in muslce glycogen levels over baseline levels if food is eaten within the correct time period.
OK, so 1 banana = xx Calories?PureClimber
Oct 15, 2003 2:39 PM
This is of interest to me as I will shortly be doing a 125 mile race with around 4500 ft of climbing. I expect it will take around 6 hours and think the most critical thing to get right will be the food.
So the query is how should I make up 300 calories per hour?
Any suggestions from people with endurance experience? Nick
Oct 15, 2003 2:48 PM
Will give you nutritional data on most common foods.
Sustained EnergyDougSloan
Oct 15, 2003 7:39 PM
I use Sustained Energy by Hammer Nutrition. It is largely maltodextrin, with no simple sugar. I use purely liquids. It doesn't taste great at first (it's an acquired taste), so you can flavor it with Hamergel. There are lots of flavors. I supplement with a good shot of Hammergel before big climbs or if I start to feel a bonk.

Make sure you get plenty of water and electrolytes, too. Without them, the energy won't do any good.

300 cal/hr, not 300 gm/hr, right? nmPdxMark
Oct 15, 2003 4:33 PM
Yeah, sorry about that. It is actually 30-60g per hour, not...Mr Nick
Oct 15, 2003 8:15 PM
every 20 minutes. Typing a little too fast I guess.
86g/hr, carbs and gells are acutally ~100Cal/oz nmcyclopathic
Oct 16, 2003 2:22 PM
Lots of great info - thanks to all who replied! (nm)OffTheBack
Oct 15, 2003 4:12 PM