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KerryIrons
Joined: 12 Jan 2004
Posts: 2917
Location: Midland, MI

7/4/18 8:56 AM

Hydration

Yesterday was a long ride with some climbing but mostly climbing dew points and temperature. Knowing it was going to be a hot day, I weighed myself just before getting on the bike and then when I got home. I lost 6.8 lb. out of 174 (3 kg out of 79) for a nearly 4% loss. And that was while taking in about 130 oz. of fluid over the 113 miles (4.6 liters in 182 km). I also took in a lot of salt, knowing what the day was going to be like. My shorts were dappled white by the time I got home even with the high humidity (usually the sweat in the short fabric hides the salt).

I never felt thirsty at any time and could have drunk more, I guess, but I doubt I could have taken in another 55 oz. (2 liters) of fluid to keep my weight loss within the magic 2% figure you hear is needed to prevent performance loss. And yes, the second half of the ride did demonstrate "performance loss." I was purposely taking it easy as the only known way to deal with the heat but I couldn't have gone much faster even if I wanted to.

I would be interested to hear the experience others are having in this heat wave.

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henoch
Joined: 12 Jan 2004
Posts: 1549

7/4/18 8:16 PM

My experiences so far SUCKED :).
I did a MTB race on Sunday, when I got to my car right after the race the dash read 111.... I felt basically sick to my stomach the whole race and really couldn't even pedal hard. didn't even feel like eating for like 5 hours after the race (usually I scarf down anything in sight right after a race)
Today I did a crit right in the midday heat, at least going faster you get a breeze, but I still felt nauseas the whole race.
So... not excitedly enjoying it :)

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4116
Location: Nashua, NH

7/5/18 5:22 AM

That sounds like borderline heatstroke. Be careful.

Kerry, FWIW I've found that during hot weather I have to plan on drinking 2 oz. of fluid per mile of the ride. When it's cool 1 oz. per mile suffices.

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KerryIrons
Joined: 12 Jan 2004
Posts: 2917
Location: Midland, MI

7/5/18 5:44 AM

fluid intake


quote:
2 oz. of fluid per mile of the ride. When it's cool 1 oz. per mile


Brian, I generally agree with these guidelines, though it is more like 1.5 ox. per mile in the heat. I doubt I could have drunk 225 oz. on my ride. That's 7 quarts. And all that I read says that you have to accept weight loss in the heat - trying to drink enough to avoid all losses would likely result in hyponatremia. At 2 oz per mile (assuming the same sweat rate) I would have not lost any weight. The issue (for me) is that even with significant salt intake, my gut just cannot process water fast enough.

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Jesus Saves
Joined: 16 Jun 2005
Posts: 1112
Location: South of Heaven

7/5/18 6:23 AM

I find prehydrating helps a bit. I will drink a lot of water the day before. Weight losd due to fluid loss will still occur, but will be less impactful on performance.

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dfcas
Joined: 11 Jan 2004
Posts: 2489
Location: hillbilly heaven

7/5/18 9:02 AM

Not sure, but I think some the weight loss comes with glycogen depletion. each gram of glycogen requires 4 grams water to suspend it and surely your tank was near empty, so i think you would lose weight even if well hydrated.

Trained people can store about 1500-1800 grams of glycogen.

I've given up riding in the heat. I never did tolerate it well and its gotten worse as I age. I prefer to ride my trainer if its over 90. AC and a big fan.

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April
Joined: 13 Dec 2003
Posts: 6382
Location: Westchester/NYC

7/5/18 9:26 AM

I'm not the best person to offer any suggestion on riding in the heat. I don't do well. And I had long ago accepted it and choose to do other things in hot days instead.

I would second the suggestion on pre-hydration based on my own experience. While I don't ride on super hot days, I found drinking lots the 24 hr prior to the ride improved my enjoyment considerably on any warm days. Also, I don't feel quite so "wasted" afterward.

I'm limited by my stomach's (in)ability to "process" in sufficient amount of fluid. If I take in more water than what my stomach can deal with, I felt bloated while at the same time dehydrated.

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lrzipris
Joined: 04 Mar 2004
Posts: 399
Location: Doylestown, PA

7/5/18 2:26 PM

As difficult as the heat and humidity make riding, I'm also leery about the air quality. That, too, makes breathing harder, for me at least.

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Marc N.
Joined: 12 Jan 2004
Posts: 442
Location: Israel

7/6/18 1:00 AM

Be real careful out there

As one who experiences your heatwave 3 months out of the year, I can`t stress enough how dangerous it is. The problem with heat is that you don`t really realize that you are in serious shit until it is too late, and it has nothing to do with hydration. Even though we have time to acclimate, all our outdoor competitions come to a halt from late June to mid September, as it is just too risky for amateur athletes to go out and make an all out effort.
For me anyway, my weekly longer ride starts at 5:30 (during the week I am already at work by this hour) and I give myself 4 hours as by 9:30 it is already in the low to mid 90`s. I could safely ride another hour but the truth is I just don`t want to as by that stage I have no real desire to be out as I know I won`t be enjoying myself, so what`s the purpose? I also go out 3-4 evenings a week (for 75 minutes), and although it is 95 or so when i leave the house, the sun is lower in the sky, the temp is dropping, and by the time I finish at dusk, things aren`t too bad. I don`t know about hydrating 24 hours before, but I find that drinking a glass or two before I leave the house helps. Also, there is no way I could drink 2 oz. per mile...for that matter, even 1.5 would be too much for me.

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Nick Payne
Joined: 10 Jan 2004
Posts: 2360
Location: Canberra, Australia

7/6/18 2:12 AM

I don't really keep a strict count of how much I drink on hot days - probably not enough. In summer here we sometimes race in 40C temperatures, though at club level the races are rarely longer than 40-50km. I find with that sort of temperature that two 750ml waterbottles only last about half or two-thirds distance, and I guzzle another one down immediately on finishing. Temperatures in the Tour Down Under quite frequently hit that sort of level as well, but even though their stages are much longer distance, at least the riders there can get additional hydration whenever they want from team or neutral support.

I find that if I'm riding at a relaxed pace, I can usually keep hydrated OK as I can drink large amounts without feeling that it's too much, whereas in a race situation, if I drink at the same rate I'll start to feel sick - the higher level of effort seems to affect my digestive processes...

We have an annual mountain Audax here in mid-summer - 200km with about 4300m of climbing. It's quite frequently fairly hot, but got a bit extreme a few years ago, when the temperature in the valleys got to 43C in the shade during the ride, and on the last couple of climbs there were riders collapsed at the sides of the road. I pulled out at the 140km point that year as I didn't think I was going to make the last 70km loop with another big climb. After that year, the organizers instituted a rule that the ride would be shortened if the forecast temperature exceeded 38C. Here is the elevation and temperature plot off my bike computer from that ride - you can see that the temperature hit 46C part way up the third climb, where the road was cut across an exposed rock face on the north face of the mountain.

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PLee
Joined: 08 Dec 2003
Posts: 3595
Location: Brooklyn, NY

7/6/18 7:37 AM

46C = 115F. Just sayin' . . . . YIKES!

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Marc N.
Joined: 12 Jan 2004
Posts: 442
Location: Israel

7/6/18 9:41 AM

44 -46

Believe me Parkin, you won`t feel the difference between 44 - 46 or 111 - 115. I honestly don`t know or understand why anyone would want to be on a bike or do anything else outside in weather like that. I would be curious if either Nick or henoch know if any other riders required hospitalization on those rides.

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April
Joined: 13 Dec 2003
Posts: 6382
Location: Westchester/NYC

7/6/18 10:11 AM

40+

For how long... and how hard you work

I don't usually do that well in heat. But one ride I did, I saw clumps of people standing underneath each and every single tree to be out of the baking sun. And I was puzzled why people were such sissies...

I later realized I was doing a shorter distance So I wasn't out for as long as those people under the tree. (a decision I made because I KNEW I don't do well in heat).

Also, those people did longer distance and were ahead of me... meaning they rode a lot faster! I bet they worked a lot harder and generated a lot more heat they need to get rid of!

Someone mentioned one maybe able to find a speed where the cooling from the wind was able to overcome the heat generated from the body. I observed the same. Granted if you're racing, that's not applicable.

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greglepore
Joined: 10 Jan 2004
Posts: 1623
Location: SE Pa, USA

7/6/18 11:59 AM

This last round of heat on the east coast got me. I haven't seen a hr over 166 in a few years, and was hitting 170 going hard on a group ride on Saturday. Freaked me out enough that I backed it down considerably. Though I was drinking enough during the ride, but yard work/car work/ moving prep during the hot days prior had probably cost me more than I thought. I have to drink almost to the point of bloat to keep up.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4116
Location: Nashua, NH

7/6/18 12:01 PM

The problem is that when the air temp is significantly higher than your body temp, you get little or no cooling effect. We experienced this in Nevada a few years ago. It was 110+ F with intermittent wind gusts. When the air was calm, you could almost feel a bubble of cooler air forming around you. When the wind blew, it felt hotter than when there was no wind. Essentially, it was reverse "wind chill". We were obviously sweating, but there was no cooling effect from it when the wind blew.

This was a completely new experience for us. Perhaps Marc or Nick have experienced something similar.

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Marc N.
Joined: 12 Jan 2004
Posts: 442
Location: Israel

7/6/18 1:17 PM

As I said, while I try to avoid being caught out when the temps are 38 or over, I have experienced exactly what you said. In the summer our weather is predictable and the afternoon winds are from the west, but in the spring and fall we often get a sharav, which is a hot wind coming out of the deserts to our east. Not only does this wind offer no relief, but make matters infinitely worse. It literally feels like an oven and breathing is an effort. If you are really unlucky, the wind often brings with it crazy amounts of dust and sand.

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henoch
Joined: 12 Jan 2004
Posts: 1549

7/6/18 2:15 PM

In all honesty I don't think it was actually 111, my car reads a bit high, but I think it was legitimately around 105-107.
No I don't believe anyone was hospitalized, I didn't see it nor hear about after the race.

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Nick Payne
Joined: 10 Jan 2004
Posts: 2360
Location: Canberra, Australia

7/6/18 3:11 PM

That particular ride I was talking about, I saw quite a number of riders on drips in the medical tent setup near the finish line.

A large part of being able to cope with high temperatures is acclimatization. After a few weeks in consistently high temperatures, your body adapts by increasing the amount of subcutaneous circulation so that it can get rid of heat more efficiently. In my younger days, I spent a few years working in the heavy construction industry in North-Western Australia, which is the hottest part of the country - we were quite often doing heavy manual labour - building railway lines, for example - with the shade temperature over 40C. I noticed several times that after coming back from holidays in cooler temperatures down south, it would take me a couple of weeks in the higher temperatures before I would start to feel comfortable again. I think the town of Marble Bar in that part of the country still holds some sort of record for the temperature having exceeded 100F for something like 116 days in a row.

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KerryIrons
Joined: 12 Jan 2004
Posts: 2917
Location: Midland, MI

7/8/18 10:50 AM

Cooling


quote:
We were obviously sweating, but there was no cooling effect from it when the wind blew.


Not true. Of course your body was actually taking on heat from the convection effects of the hot wind, but it was giving off heat through evaporation of sweat. Evaporation of water requires 0.54 Calories (food calories, or Kcal) per gram to evaporate. For old time engineers like me, that's 1,000 BTU/lb. While it is possible that your body was taking on more heat from the warm air than it was giving off from evaporation, it is unlikely. It feels like you're getting no cooling but if that were true, you'd be dead pretty quickly because your body would quickly heat up and you'd spike a fever that would kill you.

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April
Joined: 13 Dec 2003
Posts: 6382
Location: Westchester/NYC

7/8/18 12:23 PM

Engineering in real world?

I think what he meant was the hot wind did not provide ADDITIONAL cooling compare with evaporation WITHOUT wind, which is entirely possible.

Normally, wind helps to move in fresh air which is cooler and drier, to replace the air that’s warmed and saturated with your evaporated sweat. Promoting more efficient evaporation. But when the “fresh” air is above your body temperature, it maybe drier, but it’s no cooler. In fact, the hot wind destroys the cool “cocoon” of air surrounding your body...

Granted, I maybe a physicist, I’m not a thermo-engineer. So my academic analysis maybe incorrect. Critics are welcome.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4116
Location: Nashua, NH

7/8/18 1:43 PM

Based on a very small impirical data set...

...that sounds correct to me.

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Sparky
Joined: 08 Dec 2003
Posts: 16540
Location: Portland, OR

7/8/18 1:52 PM

Question is, does the higher temp of the hot air negate what the evaporation process provides as far as cooling effect?

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4116
Location: Nashua, NH

7/8/18 2:02 PM

That's certainly what it felt like. We were actually reasonably comfortable siiting in the shade, as long as the air was calm. When the wind blew, we definitely heated up.

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Andrew Lee
Joined: 10 Jan 2004
Posts: 83
Location: Anchorage

7/9/18 12:21 AM

Sweating salt out doesn't mean that you need more salt. It means that your body is self-regulating, and is ridding itself of excess salt.

You should be losing a lot of weight in a long ride. Stored glycogen needs a certain amount of water to go with it, and when you burn the energy, the water needs to go too.

There is some good information here that can also be applied to cycling:


https://www.irunfar.com/2012/07/waterlogged-a-dogma-shattering-book.html

https://www.irunfar.com/2012/08/waterlogged-part-ii-trials-questions-and-suggestions-regarding-hydration-and-ultramarathons.html

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KerryIrons
Joined: 12 Jan 2004
Posts: 2917
Location: Midland, MI

7/10/18 5:31 PM

Basic thermodynamics


quote:
does the higher temp of the hot air negate what the evaporation process provides as far as cooling effect?


In a word, no. If it did, as I said before, you would continue to heat up until you died. When the air is warmer than your skin, then you will gain more heat from the air than you will radiate into it, and the higher the wind speed against your skin, the more heat you will gain from convection. So yes, you will feel (and be) hotter when the wind is blowing than if the air is still.

But you will be cooled by evaporating sweat, and that cooling must be greater than any heat gain from the hot air or your body temp will keep rising because heat in > heat out. So we can be sure that the reverse is true: heat lost to evaporation > heat gained from hot air.

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