Sweat Production on 112 Mile Ride

Let's talk about sweat. It's salty and sticky. But it's a critical part of the hydration equation. Ideally you should replace exactly what you lose. Put too much back and you'll weigh yourself down. Don't put enough back and you'll dehydrate and your race will go to hell in a handbasket.

After an active.com article and this month's Triathlete article on Chris Legh, I decided to measure my own sweat rate. I bought a scale last night at Target and brought it to the ride this morning.

For most workouts calculating sweat loss is fairly easy. You weigh yourself before and after. Subtract the two and, viola, you know how much you lost to sweat. This assumes that you don't eat, pee or poo... and that you don't hawk massive loogies all over the place when you workout.

Today's workout was a little trickier because I took in a lot of fluid and food. And I peed a good bit. No pooping or loogies though... this time. I took a base measurement of my body with no gear before and after:

Starting Body Weight: 173 lbs - This means me in my bike shorts and jersey. No helmet. No Camelbak. No food. Just me.

End Body Weight: 168 lbs - This means me in my bike shorts and jersey. No helmet. No Camelbak. No food. Just me.

I lost 5 lbs! Wow. And while this is exciting, it's only part of the story. It doesn't really tell me how much sweat I lost. Or, more accurately, it doesn't tell me how much fluid I processed (including pee).

To take my total weight into account I had to weigh myself and include everything that I consumed. To do this I weighed myself at the beginning with my camelbak and food.

Starting Loaded Weight: 181.5 lbs - This means me, my camelbak and food.

I then wrote down how much water I added to my system (to my camelbak) during the ride. I stopped twice and filled up completely once and filled up 1/2 a second time. To get the weight of just the water in the camelbak I had to weigh it with and without. This is the least scientific figure in this analysis.

Weight of water added throughout ride: 4 lbs + 2 lbs = 6 lbs

So, to get my total loaded weight I add the start loaded weight to the extra weight that I added on the ride.

Total Loaded Weight: 187.5 lbs

Then I need to see what my loaded weight is after the ride. And since there was some water left over in the camelbak, I had to take that into account so I weighed myself after the ride with the camelbak and any remaining food/water.

End Loaded Weight: 173.5 lbs

To calculate the weight of the fluid that I processed throughout the ride I subtract the end loaded weight from the start loaded weight (187.5 lbs - 173.5 lbs):

Weight of Fluid Processed: 14 lbs

Wow! I processed 14 lbs out of my body today! That's a good bit of water.

Active.com tells me that I should be drinking 16 oz for every 1 lb that I process. According to that, I should have had 264 oz to drink.

My camelbak is 72 oz. I drank through it once completely (72 oz), once halfway (36 oz) and once 1/4 of the way (18 oz). This means that I drank only 126 oz!

Wow! This must be affecting my performance.

While my drink measurement technique isn't that accurate, it's clear to see that I'm not drinking enough. I should be drinking the entire camelbak 3.67 times throughout the workout. I came nowhere close.

This rough analysis is certianly helpful but in the future I need to improve my sweat rate calculation a lot:

First, I need to do more of a closed-system measurement. I'm thinking about a swim. One hour. No drinking. Simple. Measure my weight before and after. Anything lost was lost to sweat.

Second, I need to more accurately measure my fluid intake on the bike. I'm thinking about moving to water bottles for the next ride so that I know exactly how many ounces I'm drinking.

Third, I need to measure my pee on long rides. I'm thinking that I'll bring a spare water bottle, mark it off with ounce lines and pee into it. Of course I'll dump it out, but I'll be able to record the amount that I peed out. This would give me a great breakdown of pee vs. sweat production.

Fourth, I need to compare these sweat rates across the seasons. The body adapts to heat by outputting more sweat with the same amount of salt. To see if you're adapting, lick your arm on a run in the summer. It's not very salty. Do the same at the end of the winter. Salty. Sweat rates change.