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Bonking - or Heat Exhaustion?

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Bonking - or Heat Exhaustion?

Old 07-16-06, 07:28 AM
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Bonking - or Heat Exhaustion?

Yikes! I figured BikeForums has all the engineering and coaching expertise, so why not medical advice?

Yesterday I went out on what was supposed to be a long, reasonably slow ride. I had heard that it was supposed to be about 85 degrees or so, so I knew I was going to need a lot of water. I was going for a 60-70 miler; usually I don't need any caloric intake for that range. In any case, I didn't take in any calories during the ride.

To make a long story short, halfway through the ride, about 35 miles from home, I get a semi-emergency call, and need to book it back home. I figured I take the chance against bonking (there's a couple of places I could stop if I felt it coming) and go reasonably hard. I had already taken in ~2.5 liters of water, and took in another ~3 liters coming back.

It didn't feel that warm to me at the time - but it was quite sunny, and although I didn't know it, it was ~92 degrees; and would climb to ~94 degrees before I was done. It might have been more, since I was on tarmac for the entire trip.

In the past, when I have bonked; I've felt very tired - not only muscularly exhausted, but quite sleepy - like I should take a nap before I get home.

This time was different. I didn't feel sleepy. But about four-five miles from home, I was nauseous (dry heaving) and exhausted. I had a headache (semi-normal for me), but was getting a little dizzy (not normal). I could barely drink any water, but forced myself to drink anyway. My breathing was odd - it was almost like I couldn't breathe fast enough; even though my output had sunk to about 100 watts or so.

When I got home, I took a tepid shower, tried to drink some more water, but couldn't drink nearly as much as I felt was prudent. My breathing for the first half hour or so after I got home was still odd. About fifteen minutes post-ride, my pulse was 77 - normally my RHR is ~55. I forced down some OJ (in case this was bonking symptoms that I just had never experienced before), but couldn't eat anything. Before the ride, I had weighed 166.2; after the ride, even with all the water, I weighed 163.4 lbs.

During this entire experience, I didn't feel 'hot' (and I didn't know how hot it actually was outside), so I didn't even think about heat exhaustion until after the symptoms were almost over.

Opinions? Right now I'm thinking this was heat exhaustion, not bonking, but I'm not sure. Has anyone ever had these symptoms during a bonk?
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Old 07-16-06, 07:35 AM
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Originally Posted by ElJamoquio
Before the ride, I had weighed 166.2; after the ride, even with all the water, I weighed 163.4 lbs.
Sounds like you lost a lot of fluid due to the heat and it caught up to you. I normally use a bit less than 1 water bottle per hour but on hot days it can almost double.

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Old 07-16-06, 07:59 AM
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I think the general wisdom around here is you should be taking in 200-300 calories per hour while riding and drinking something with some sodium in it as well ( gatorade, accelerade, whatever) besides water.
Not eating at all is just asking for trouble, IMHO.
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Old 07-16-06, 08:24 AM
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A 3# weight loss is not unusual for a ride like yours, especially in the summer.

The point of sports drinks with carbs and sugars in them is that the fluid is absorbed so much more quickly from the gut than water. For every part of carb or sugar that's absorbed from the gut 5 parts of water are drawn with it. And that generally happens in the duodenum, the part of the small intestine just below the stomach. Plain water isn't absorbed until much later in the digestive process, and is often retained in the gut to aid in digestion.

On cool days or when there's not much demand for it, it's not a problem. But when there is a demand for maintaining blood sugar and hydration (hot, cold, physical exertion, stress) it becomes much more important. And for people that have pre-existing health conditions (diabetes, hypertension, obesity, etc) its quite critical.
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Old 07-16-06, 09:20 AM
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Sound like a little of both. You need more calories and you need to go slower in the heat. The more you train in the heat the more you get used to it, but do it gradually, you can get into trouble. Not feeling hot is a syptom of heat exhaustion I believe.

I would say it was a full size heat exhaustion with the help of bonk from no fuel.
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Old 07-16-06, 01:37 PM
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Losing 3 lbs on the ride doesn't sound like much of an issue. Yesterday I rode 70 miles in 95 degree heat and went through 11 bottles of fluids. Before the ride I was 210 lbs, afterward I was 202 lbs. But, I ate enough and hydrated as much as I could. Plus I tend to pre-hydrate, so my actual weight probably should have been around 208.

I think that for that long of a ride you need to eat more. Your body generally isn't going to store that much energy so you'll have to supplement your body's energy reserves.
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Old 07-16-06, 01:46 PM
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Originally Posted by dekalbSTEEL
I think the general wisdom around here is you should be taking in 200-300 calories per hour while riding and drinking something with some sodium in it as well ( gatorade, accelerade, whatever) besides water.
Not eating at all is just asking for trouble, IMHO.
I just read an article from Carmichael Training

In general it says, you want to maintain a steady intake of 30-60 grams of carbohydrate per hour. That equates to about 200 cal from carbohydrates and includes any sports drinks. Your stomach can only digest around 50 grams per hour so you want a balanced, steady intake. Amounts substantially over that amount are just stored in your stomach and can create differing amounts of stomach distress
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Old 07-16-06, 01:46 PM
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The stuff you're describing sounds more like heat exhaustion to me, but it's hard to tell for sure.

Another issue that I run into occasionally is inadequate loading of carbs in the day before your ride. As your HR increases, more of your calories are burned from carbohydrate. So while you may have had plenty to make your planned ride, it could be that the intensity of the ride home used up your glycogen stores, and once you're there your body can't absorb enough during exercise to make it up.

Just my guesses...

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Old 07-16-06, 02:32 PM
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I would say this is more of a heat exhaustion issue than a true bonk. If you're not acclimated to the heat, you need to take a few shorter rides to acclimate yourself or turn the a/c off in your car when running around the city. I find this helps quite a bit. You gotta drink more than water when you're on a ride of 90 minutes or more. Any good hydration drink will help you out. (Cytomax, GU2O, Endurox, Accelerade, any of those works well I've found though I tend to lean toward GU2O) I use a camelback when going longer than 2 1/2 hours since I have a couple of 30 oz water bottles and 2 1/2 hours is the limit with them. Normally you should intake approximately 20 oz of fluid every hour, but the hotter it gets, the more you're going to need. Here in Texas, 90-ish degrees doesn't sound too bad right now as it is 102 degrees at the moment.

You only have enough glycogen in your muscles for about 3 hours of riding and if you don't take any in, you'll ride slower, lose power, and you can do damage to your legs. I find three things help me when on rides of longer than 2 hours: as mentioned by Dr. Pete, one is to eat plenty of carbs the night before, the second is to eat approximately 400 calories or so an hour or more before I ride (hard to do this in the morning) and the other is to make sure I eat every 45 minutes or so when I'm on the bike, whether it's gel form or otherwise. My legs feel significantly better when I do ALL these things.
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Old 07-16-06, 03:19 PM
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I had a similar experience recently on a planned 110 mile ride, only made 90. I drank plenty of water but didn't replace electrolytes. After a few days to recover I went back to finish the last 20 with >4000 ft climb. This time I took endurolytes along with the water. Despite the heat I made it up the mountain, a bit slow but no health issues this time.
That 20 miles was more difficult than the 90 because of the climbing.
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Old 07-16-06, 07:20 PM
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I just read an article recently about how athletes (marathoner runners were the example, I think) can actually over-hydrate during running. I don't remember the symptoms that the article named, but you say you drank a total of 5.5 liters during the ride. Again, I can't remember the details of the article, but that's a lot of water. Just a thought.
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Old 07-16-06, 07:37 PM
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Originally Posted by benc
I just read an article recently about how athletes (marathoner runners were the example, I think) can actually over-hydrate during running. I don't remember the symptoms that the article named, but you say you drank a total of 5.5 liters during the ride. Again, I can't remember the details of the article, but that's a lot of water. Just a thought.
It's the ratio of electrolytes(salts) to total body water that gets out of wack when you drink too much water with replacing lost salts. It's a process that's accelerated in hot weather.
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Old 07-16-06, 09:39 PM
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Originally Posted by ElJamoquio
...I was going for a 60-70 miler; usually I don't need any caloric intake for that range. In any case, I didn't take in any calories during the ride....
umm, there's you're problem, sir...

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Old 07-17-06, 02:05 PM
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All:

Thanks for the advice. Normally I don't require any calories for a slow (~17 MPH) sixty-miler. Really. I knew I was pushing things with bumping up the pace, but I figured I could stop and pick something up if I felt the low blood sugar coming. Normally I feel it - on Saturday I didn't.

I'm almost positive now that it was heat exhaustion causing at least 80% of it.
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Old 07-17-06, 05:08 PM
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Sounds like the first stage of heat exhaustion to me. Most people don't get nauseated when they bonk. I get muscle cramps, nausea and chills when I get into the overheated zone.
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Old 07-17-06, 05:58 PM
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Originally Posted by benc
I just read an article recently about how athletes (marathoner runners were the example, I think) can actually over-hydrate during running. I don't remember the symptoms that the article named, but you say you drank a total of 5.5 liters during the ride. Again, I can't remember the details of the article, but that's a lot of water. Just a thought.
https://www.ultracycling.com/nutritio..._too_much.html
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Old 07-17-06, 06:00 PM
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That URL was corrupted.

https://www.ultracycling.com/nutritio..._too_much.html

"Overhydration does not equal good hydration. On the contrary it is dangerous and should be avoided as carefully as underhydration."
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Old 09-07-06, 03:24 PM
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I really believe that you suffered from Heat Exhaustion...I had the same thing happen to me a few weeks back...Very light headed, weird breathing, my skin felt clamey and moist. I just hit the wall. It didn't feel hot out at all, but the temp was 92 degrees. I had to force myself to drink water. I got home and layed down on my concrete basement floor to bring my body temp down...This works fast to get your body temp down. And rested for two days afterwards. I felt like I was dying.
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Old 09-07-06, 04:41 PM
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Originally Posted by 2manybikes
Sound like a little of both. You need more calories and you need to go slower in the heat. The more you train in the heat the more you get used to it, but do it gradually, you can get into trouble. Not feeling hot is a syptom of heat exhaustion I believe.

I would say it was a full size heat exhaustion with the help of bonk from no fuel.
+1. A little of both. Or rather, a fair bit of both. In Texas I typically take 70oz of pure water and 2x 24oz bottle of sports drink that has been mixed slightly weak. On top of that I try to do one gel or other type of food per 25mi.
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