Sweating It

It's Gonna be HOT the Next Couple of Weeks! NWS Data for DFW from 1898 Through 2009. Date the Hottest Day Occurs.

Due to my recent hospital visit, recounted here, I now pay a lot more attention to hydration in warm weather. For example, I have learned that I lose about two pounds of fluid during my ride to work if it is about 80F. That fluid loss increases substantially for the trip home when it is around 100F. In North Texas, we are now entering the two-week period when the hottest day of the year is most likely to occur. The forecast for next week is for 100F+ days all week, so we may hit our high temperature for the year right on schedule.

Recently, I made another discovery. I discovered just how much even a “high ventilation” helmet reduces evaporative head cooling; a subject of unusual interest for the hottest fortnight of the year. Please don’t get into the safety merits of helmets here, this is just observation. It came about thusly.

Headsweat Do Rag, Normally Worn Underneath the Helmet

Normally, I wear a helmet on my commute. Underneath the helmet, I wear a moisture wicking “Headsweat” do rag. Besides wicking moisture, it helps block sun on the return trip home, and it reduces the amount of sweat I drip on my shoe. In the summer, the helmet I use is one of those with the big “wind tunnel” vents. The hype actually tries to create the impression that air flow is better than with no helmet at all (of course, nobody shows any actual data). Despite all this, by the time I get to work the Headsweat has absorbed as much as possible, and resembles something just retrieved from a puddle. On the way home, the Headsweat simply overloads.

Big Vents Really Don't Help Cooling a Lot

Without the helmet, things are quite different. As it turns out, I forgot to put my helmet on recently, and was over a mile home before I noticed. I DID have the Headsweat on. Riding on with this configuration, I arrived at work and noticed that the Headsweat was MUCH drier. One of two things is happening. Either the helmet is causing me to sweat more, or it reduces evaporative cooling a lot. Anybody know of any credible studies comparing how often people get heat exhaustion WITHOUT helmets versus wearing $20 helmets they got at Wallyworld, versus wearing $200 bike shop helmets?

Now, before someone decides he/she needs to accuse me of being an idiot for not wearing a helmet from the time I lift my head from the pillow, or of being an idiot for EVER wearing one, I will note that I still plan to wear a helmet on my commute riding. Someday I may do a post on why, but not today. THIS post is dedicated to sweat.
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"Bikingail" sez "Hydrate - OR ELSE I'll Shoot Ya!"

SPEAKING OF WHICH, there’s an interesting article on North Texas hot weather exercising in the Dallas Morning News. It describes recent changes in what we’re told about hydration, among other things. Instead of “drink before you’re thirsty,” it advocates “drink WHEN you’re thirsty.” I definitely subscribe to their “acclimate” theory. I find that, this time of year, 100F weather presents few problems for a 20 mile commute. To date, 107F is my upper bike commute temperature limit. The official, all-time high temperature at DFW was 113F, set on June 27, 1980. As “bikingail” says, “hydrate, hydrate, hydrate!”

It's Risen about a Half Degree, Plus or Minus About Three Degrees.