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Staying Hydrated During Long Rides on Hot Days Is a Major Challenge

Yesterday was the hottest day of the year— up to 100° F in my area, and 91° F in shady areas that are normally 20° cooler. Also, the humidity was unusually high due to recent rains.

I weighed myself on a medical grade scale good to 1/10 pound before and after my 3-hour ride (weights here are total riding weight of rider + all clothing + bike + water + food).

I couldn’t believe just how much weight had disappeared! I accounted for all losses as shown below, but the one factor I don’t know is how much body mass is lost to supply the 1800 calories I didn’t eat (I consumed 500 calories of energy gel during a 2300 calorie ride, so 2319 - 500 calories had to come from existing body energy stores, e.g., fat and glycogen).

I know these weights are not a mistake, because they are consistent with results on other days that were not so hot, and with somewhat shorter rides.

I noted an increase in heart rate as the ride progressed (heart rate drift), so dehydration was definitely a factor. I also noted a decrease in power output. Which is very bad news if this had been an 8-10 hour ride.

In short, my hydration was entirely inadequate, and the following need answering:

  • How much more aggressively can I drink during a ride without drinking too much (and while also keeping electrolyte balance)?
  • Should fluid intake start earlier in the ride? Probably unwise to wait for an hour to pass before starting to drink.

It is my understanding that the stomach can absorb up to 1 liter of fluid per hour, which means I should have been able to consume 3 liters during my 3-hour ride. Still, that is only 1/2 liter more than I actually consumed, and it would not have been not enough.

Weight-loss during 3-hour hard ride on 90-100° F day
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