will dehne

I have this flat Illinois bike path and use it for training. It is 11 mile one way. I always do at least one loop.
I forgot my water bottles and decided to train anyway. The temperature was around F 60 degrees. I often do 1 hour exercise on a trainer without water.

Well, I matched my record time of 11 miles in 30 minutes going one way. (HRM 145)
On return I had a hell of a time going 15 to 18 MPH. I was not smart enough to figure out why.
Coming home I went on the scale. My weight dropped by 4 lb.
This means dehydration without any pain except performance loss!
Question: Does this match someone else experience? I am sure trying to keep hydrated after that little surprise.

Guest

Yeah. I did this gawd-aweful century that claimed to be supported, but it turned out to pretty much not be supported. When I got on a scale, I'd dropped about 5 pounds. Maybe more. It was aweful. But I do know from now on, when I do a century, I'll have the hydration pack, along with my water bottle carriers filled, and I will ensure that it is a true supported ride, or else I'm not doing it.

Koffee

will dehne

koffee: You have been doing this longer and more than I have. Dehydration on a long trip and hot day is clear to me. I have suffered those consequences.

What I did not realize until this week is that an intense ride for one (1) hour in F 60 degrees can make me loose 3-4 lb. of water. Does that match what you know? Or do I have to test that again? As you probably know, I am going on a cross country tour and I do not want mistakes like that on that tour. Thanks.

chrisesposito

Dehydration from an intense and extended effort is a problem at any temperature. I spend my winters cross country ski racing and on the longer races (30K and up), hydration is just as significant an issue as it is on the bike in mid-summer.

Guest

Very true. Dehydration isn't about heat, it's about not getting enough water. The body only makes 20% of its needed water from metabolic pathways. The other 80% must be drank.

Why do you have to "test" anything anyway? I thought you understood this was a bad thing, and you were just curious about it.

Koffee

webist

Moisture also leaves your body in substantial amounts through respiration. This too is true at any temperature.

jrennie

4lbs of water loss(approx 1/2 gallon I'm guessing) in only 1/2 hour? Is that even possible?

will dehne

Koffee: Please, I am not irresponsible. Circumstances are such that one cannot always have food or water where I go. I bike a lot on trails which may or may not have water stations. Now that I realize this problem I will have more bottles on my bike.

I did not know that I could deplete my body in one hour. In the past I have been going at 10-15 miles an hour. At that speed dehydration is not an issue for me unless it is 100 degrees. This slower pace I did for ten years. (I am 190 lb., 74" tall and not skinny)
Apparently going at 20 MPH+++ it is a different story. This speed is relatively new for me. Perhaps 18-24 months. So this old dog has to learn new tricks. I could not believe my eyes when I looked at the scale after above one hour ride.
So, yes, without your comments I would check it again. Now I will not. Thanks.

will dehne

Exactly my question. My weight went from 193.?? down to 189.??
So I am not claiming precision. I was caught by surprise.
However I have seen often 2 lb. loss after one hour exercise. That would not surprise me.

will dehne

This is true. I train on a trainer at a lesser intensity than the trial above. On a trainer I do HR 120. There is a lot of sweat on the floor with the trainer and little sweat at the high intensity ride. (HR 145)

I had these signs that things are not OK:
No power on the return trip.
Weight loss.
Jittery feeling.
Lots of sweat was not one of the signs.

will dehne

This I did NOT know. This would explain this. I assumed that ambient temperature was all what mattered.
Until 2 years ago I was 240 lb. and never exercised at this intensity. (since I was 25)
Now I exercise very intensely and often. Thanks.

will dehne

OH, I just read your post again. I did not say "in only 1/2 hour". I said ONE hour.
I went 11 miles in 1/2 hour PLUS more than 1/2 hour at 15-18 MPH.
So that is 22 miles in over one hour. I often do that in 60 to 70 minutes depending on conditions.

Guest

Seriously, I'm glad you're not irresponsible. I was alarmed for a moment. *whew*

How do you know you lost 4 pounds on that one ride, btw? It may make more sense that you lost that weight over time and weren't aware of it between your last weigh in and after you took your ride. Maybe you lost just a pound or two, tops?

Just wondering.

Koffee

will dehne

Always go on the scale before and after. This is not a precision scale and I am allowing 3.5 to 4 lb.
BTW
I was 240 lb. and my weight loss for one hour MILD exercise, without water intake, was always 2 lb. (Reclining stationary bike at about 80 RPM and set at 700 calories/HR) My HR was never above 120 if that.

Now I am 190 lb. and exercise at a HR of 140++. I think we should expect more water loss in one hour. I just did not think it would be double.

Post #4 above gave me a useful answer and you confirmed it. I put too much weight on ambient temperature. Thanks.

DannoXYZ 

This is because it's the core body-temperature that dictates perspiration. Your core is 98.6-F and will increase with exertion, the higher the effort, the higher the temperature increase. You'll sweat a certain amount in proportion to the increase in temperature of your core and muscles. The only thing the outside ambient temperature will determine is then how quickly this sweat evaporates. Colder temperatures means the sweat will not evaporate very quickly whereas higher temperatures will quickly evaporate the sweat and cool the skin off.

It may appear counter-intuitive. Kinda like why desert-dwellers wear full-body robes of dark colors...

will dehne

Danno:
May I compliment you on your well written responses? This BF is lucky to have you.
Thanks.
I was misguided about the relative importance of ambient temperature.
Biking around at leisurely pace did not force me to recognize that. A more challenging biking does. There is a lot of related things I had to learn in these two years. Equipment, Nutrition, Hydration, Prevent Infection, Clothing, Cadence, Interval training, Safety, Bike Fitting, etc.
I think the Veterans may underestimate how much Newbies have to learn fast.