I Am a Urine Factory: Fluid Loss on 112 Mile Ride - 37.824 oz/hr
7 Hour
8 Minute
PM
Finally getting around to writing up my little weekend hydration study. Trying to figure out my optimal hydration strategy for long races. A few weeks ago I measured sweat rate but in doing so uncovered some ways to improve the accuracy. On last weekend's 112 mile ride I implemented those improvements.
The main improvement required was a differentiation between sweat loss and urine loss. I had to measure pee so that I could distinguish between the two.
I did the usual weight measurements at the beginning:
Start weight with no gear: 173.5 lbs
Start weight with gear: 182.0 lbs (full camelbak, food, extra water bottle)
Before the ride I used a measuring cup and a permanent marker (a generic Sharpie ripoff... sorry Kurt Busch). I marked off 100 mL increments on the extra water bottle. My plan was to more accurately measure the amount of water that I added to the system (me being the system) throughout the ride. This includes any time that I stop for water at a bathroom or water fountain. Any extra water needed to be measured.
I also marked one of those bottled water bottles that you get at the supermarket. 100mL increments. I forget the brand, but it was a lightweight plastic that I could crush down and put into the camelbak. The P3 doesn't have two water bottle holders... I need to get one of those behind-the-seat holders. So, this was my pee cup. I had to measure any urine that I peed out throughout the ride. My plan was to pee into the cup, check the amount and then pour it out.
Bringing a pen and paper is an improvement for the next ride. I had to remember two numbers throughout the ride: amount peed and amount of water added. Not a big deal.
At this point I've implemented two improvements: measuring urine and measuring added water. I also wanted to improve my drinking frequency. I learned on the first ride that I wasn't drinking enough and was becoming dehydrated. So I drank like a fish.
I had to pee 20 minutes into the ride. Stopped on the side of the trail. Still very early and not too many people around. Stepped into the woods and peed into the bottle. 300 mL. Poured it out. Made mental note. Off I went.
Kept drinking a lot of water.
Twenty minutes later. Pee break.
Drink water.
Twenty minutes later. Pee break.
You get the pEEcture.
The problem was this: the temp was cool on this ride. Very cool. I had to ride hard just to prevent chill bumps for the first hour or so. Around 54 degrees. I was doing almost zero sweating. But I was drinking like crazy.
By the fifth pee break I was really annoyed so I slowed down my drinking rate a bit. I was averaging 325 mL on each pee. 425 mL on one of the bigger ones. Not sure if this means I have a big bladder or a little one.
By the end of the day I had peed 2900 mL! About ten pee breaks.
I filled up the bottle twice, adding it to the camelbak. That's 1600 mL of water added to the system.
I figured that I'd weigh as much as or even more than I did at the beginning. Even though the heat did eventually get me sweating, it wasn't anything like past rides. I admit that given the initial pee frenzy I may have slowed my drinking too much.
End weight with no gear: 167.5 lbs
End weight with gear: 171.0 lbs (remaining camelbak, food, extra water bottle)
I was surprised. All that peeing took it out of me. I lost 6 lbs on the ride. Pee factory.
Let's look at the numbers:
1000 mL of water weighs 2.200786 lbs
Our first goal is to convert the amount of water added to the system so that we have a complete starting weight. 1600 ml weighs 3.5212576 lbs.
So our starting weight is:
Start loaded weight with gear: 185.5212 lbs (full camelbak, food, extra water bottle, and all extra water added throughout ride)
We already have the final loaded end weight: 171.0 lbs
This means that throughout the ride I somehow dropped 14.5212 lbs of fluid.
Ok, this is where the last analysis ended. But today I can continue the analysis. I can break this down to urine vs. sweat. I'm betting on the urine.
I lost 2900 ml of urine which weighed 6.3822 lbs. Very surpsiring! The majority of the fluid loss was still through sweat, despite peeing all the time.
Loss via sweat: 8.1389 lbs.
Loss via urine: 6.3822 lbs.
Loss total: 14.5212.
Now I want to convert these to numbers that I can use while working out.
The total time of the workout was 5.883 hours.
Sweat loss/hr: 1.383 lbs/hr
Urine loss/hr: 1.084 lbs/hr
Total loss/hr: 2.468 lbs/hr
Now let's convert to gallons/hr (1 gallon = 8.35 lbs):
Sweat loss/hr: .1656 gal/hr
Urine loss/hr: .1298 gal/hr
Total loss/hr: .2955 gal/hr
Now let's convert to ounces/hr:
Sweat loss/hr: 21.1968 oz/hr
Urine loss/hr: 16.6144 oz/hr
Total loss/hr: 37.824 oz/hr
So, what do all of these number show me? The most interesting thing is that despite very different temperature conditions and drinking strategies I dropped about the same amount of fluid as I did on the previous 112 mile ride... about 14 lbs. This sticks with something that says that we all seem to dehydrate to a certain point and then stop.
In total body weight I lost about six lbs which is 3.5% of my body weight. The magic 3% is what I generally read in the literature as the point where most of us stop losing fluid and start losing performance.
Not good. Bottom line is that even on a ride that felt cool where I thought I was drinking a lot I still got dehydrated. My performance suffered and I blamed it on early pace setting. Probably not true. Now that I see these numbers I have to blame hydration again.
My rate of loss was lower than a high intensity spinning class and higher than a low intensity swim. This makes sense.
So next time I need to drink smarter. If you're reading this (thanks), be careful. Many people are over-hydrating themselves. In this month's Triathlete magazine there's a Speed Lab Science Q&A about hyponatremia (over-hydration).
In many cases the symptoms of hyponatremia are mistaken for dehydration, the patiend is placed on IV fluids and promptly dies. ... The incidence of symptomatic hyponatremia among athletes seeking medical care had been reported to be as high as 23 percent in the New Zealand Ironman, while 5 percent of athletes seeking medical care at the Hawaii Ironman were hyponatremic.
While I'm under-hydrating, some people are over-hydrating. Be careful. Check your own numbers. What you think you're doing may be quite different than what you're actually doing. I was way off base.
But I'm learning. Need to drink more. I'm looking forward to a hot and sweaty day to measure pee vs. sweat.
I'll need more data points to build a case for hydration vs. temperature. And, in truth, I haven't even begun to measure my real fluid requirements because I keep going out there and dehydrating myself. Once I stop doing that I'll actually find my real numbers.
But that's what makes it fun. Thanks for reading. They say that for every equation you put into a science book you lose 10% of the readers. No real equations in this one but it's not exactly exciting stuff. You're appreciated.
CK from ck-blog.com Writes About dNeero