In the Tour de France the riders refer to the stages between the Pyrenees and the Alps as the Dog Days. The 198K flat stage from Mure to Rodez was almost at sea level. The ambient temperature reached 97F (36C) and it was a scorching 108F (42C) coming off the tarmac. Jens Voigt said in his commentary that the tarmac gets so hot that it almost melts tires. They get so hot that it sounds like glue on the outside of tires as they’re rolling.
According to race leader Chris Froome, “When it’s hot like that, you need a new bottle of water every 10-15 minutes. It was tough.” That’s 20 to 30 bottles over a 5-hour stage!
Even with that much fluid on a hot day a rider can’t get enough and gets dehydrated. Dehydration of 2 – 3% doesn’t affect performance, though — just look at the sprints! However, significant dehydration does affect the day’s riding, as well as recovery for the next day.
Most of the heat for a rider comes from the rider’s own body, which is only 20 to 40% efficient. That means that only 20 to 40% of the energy that a racer gets from eating goes into forward motion, and the rest produces heat. This is why even on a moderate day, overheating can be an issue.
And it’s why Jens Zemke, the MTN-Qhubeka South African team director, told his riders not to start dumping water on themselves until halfway through the race because once they started they’d keep doing it. Water does a far better job of cooling the body if a rider drinks it than if he pours it over his head, although dousing himself does feel good.
A rider is weighed before and after a stage and then drinks 1.5 times his post-race water deficit. Richie Porte, Chris Froome’s chief lieutenant, weighs 137 pounds (62 kg). If he gets just 3% dehydrated during a stage, then he’ll be down almost 4 pounds (2 kg) and he’ll drink 6 pints (3 liters). He drinks more than he lost so that he is both fully rehydrated and is getting enough fluid for his ongoing needs.
Heat Affects All of Us, Not Just the Pros
I twice won the Furnace Creek 508 racing through Death Valley. The temperature reached 108F (42C), and I won in part because I knew the best way to stay hydrated and what electrolytes I needed. I’ve further honed my hydration knowledge since my racing days, working with athletes doing hot events for over 20 years.
(Pictured is what I carry for a three-hour ride: a CamelBak, two bottles, two wet socks to keep the bottles cool, and snacks. All are important.)
Because most of the heat we suffer from is generated internally, developing a personal strategy for riding in the heat and a personal hydration and electrolyte plan is important for all riders.
This does not mean drinking as much as possible, which risks hyponatremia (low blood sodium), a potentially fatal condition. Rather, experts agree that you should just drink enough to satisfy your thirst.
I’ve written an eArticle that explains in detail what you should drink and what electrolytes you need when you feel hot.
- How sweat cools you
- Assessing your sweat rate and composition
- How much should you drink?
- Fluid replacement
- Electrolyte replacement
- Electrolyte replacement drinks
- Electrolyte replacement supplements
- Electrolyte replacement food
- Hydration-related problems
The information-packed 21 pages are $4.99, and just $4.24 for our Premium Members.
This article complements Cycling in the Heat, Part 1: Ride Management, which prepares you to ride when your body heats up no matter where you live, or how you ride. These articles are relevant to fitness-minded recreational cyclists and performance-minded riders alike.
Both Part 1 and Part 2 of the Cycling in the Heat series are available together in a cost-saving bundle.