Watching the Tour de France, every so often you’ll hear commentator Phil Liggett say that the riders have stopped for a “nature break,” and the camera pans to something else. Maybe you’ve noticed that during a multi-hour race the riders will only stop once or twice.
A reader, Andy, emailed me about nature breaks: “I learned how little time one of my friends, Mike, was off the bike during a recent 12-hour race. He reported that he was off the bike just two minutes out of 12 hours! The course was hilly and the weather around 60 degrees, overcast, and windy. With no scientific data, it seems to me that toxins should to be flushed more frequently.”
I inquired and Mike reported that he has done three 12-hour time trials so far this year. Here’s what he consumed during each, along with other related stats:
|Race||Ave. Temp||Fluid||# 20 oz. Bottles||Pee Stops||Miles|
|Sebring Feb. 11, 2017||75F||Water||9||234|
|Bessies Creek Apr. 8, 2017||70F||Water||8||1||219 (brutal headwind)|
|Maryland Enduro May 20, 2017||65F||Homemade Mix*||10||2||214 (lots of hills)|
Note that the temperature was only 65F on May 20; however, Mike consumed 10 bottles! Why so much? Because most of the heat you experience is generated by your body, which is only about 25% efficient. For every four calories you consume, only one calorie provides energy to move you forward—and the other three calories produce heat.
How much hydration is enough?
Did Mike drink enough and take enough nature breaks? One sign is whether he urinated every two to three hours (he stopped about every four hours) with a good clear or pale yellow stream. He reported, “I didn’t notice pee color. I know that’s relevant, but my mind is elsewhere when racing! I never felt any sensation of bloating.”
If he was drinking significantly less than he was sweating out, then he was getting dehydrated and wouldn’t have urinated. On the other hand, if he was drinking too much and not urinating, then he was retaining fluid and developing Exercise-associated Hyponatremia (EAH).
The only way to tell if Mike (or any rider) is getting dehydrated or retaining fluid is to weigh the rider before and after a ride (and during the ride if it’s a long one.)
Under 2% dehydration is okay
Dehydration is measured as a percentage of your body weight. If you weigh yourself before a ride and your weight is 150 lbs (68 kg) and then you get on the scale after a ride and your weight is down three lbs (1.4 kg), you’re 2% dehydrated. Mild to moderate dehydration doesn’t affect performance significantly. The human body can only absorb so much fluid per hour. On a hot stage riding hard, the pros can’t consume enough fluid to stay hydrated — but they sure sprint well!
EAH is a fluid-electrolyte disorder caused by a decrease in sodium in the blood (hyponatremia) during or up to 24 hours after prolonged physical activity. This disorder can develop when endurance event athletes drink more fluid, usually water or sports drinks, than their kidneys can excrete. This excess fluid can severely dilute the level of sodium in the blood that is needed for organs, especially the brain, to function properly. As fluid is retained, the brain swells and pushes against the skull, a potentially fatal condition.
The symptoms include impaired performance, nausea, vomiting, headache, bloating, and swelling of hands, legs, and feet. As water retention increases, weight gain may also occur. If you see puffiness around your gloves, a ring on a finger or the top of your socks, then you are retaining fluid. Stop drinking until you’ve urinated out all of the excess fluid and the puffiness is gone.
If you or another rider has a headache, particularly in the front part of the brain, the rider may also be retaining fluid. If the rider has a headache and is confused or disoriented the brain is severely affected — call 911!
You can learn more about the science of riding in the heat, and managing your fluids and electrolytes, in my two-eArticle Cycling in the Heat Bundle.
- Cycling in the Heat, Part 1: Ride Management is 19 pages and covers how to acclimate to hot conditions, how to train in hot months, what to wear, eat and drink, how to cool down if you overheat, and how to deal with heat-related problems.
- Cycling in the Heat, Part 2: Hydration Management is 21 pages and covers how to determine how much you should drink depending on your physiology and sweat rate, how best to replace your fluids and electrolytes, the contents of different sports drinks, how to make your own electrolyte replacement drinks, how to rehydrate after a ride, and how to deal with hydration-related problems.
My Summer Riding bundle contains both of the Cycling in the Heat articles as well as articles on handling cramps and learning the nutrition and hydration secrets of the pros:
- Cycling in the Heat, Part 1: Ride Management, 19 pages
- Cycling in the Heat, Part 2: Hydration Management, 21pages
- Preventing and Treating Cramps: The 10 pages give you a detailed look into the causes of cramps so that you can understand and implement prevention techniques. It provides tips (both on-bike and off-bike, including photos) for breaking and flushing cramps.
- Eating and Drinking Like the Pros: The 14 pages are based on research about what pro riders consume before, during and after a stage. The findings hold lessons and benefits for cyclists at all levels. Eating and drinking like the pros offers recreational riders the same nutritional benefits, which you can customize to your own needs – typically at a fraction of the cost of commercial sports food and drink, if you choose to make your own. I worked with a professor of nutrition and an expert on hydration and electrolytes (both experts are cyclists) in creating recipes for both sports drinks and food.
Drink enough but not too much
You’ve probably heard “Eat before you are hungry and drink before you are thirsty.” Eating early and often is still good advice, but drinking before you are thirsty is no longer recommended by medical experts because of the risk of developing EAH.
Current researchers on hydration and hyponatremia recommends a simple rule of thumb: Drink if you are thirsty, but otherwise don’t drink.
How much do you sweat?
On average if you are riding in moderate conditions — that is, you aren’t gaining heat from the environment — each hour you’ll produce 600 to 800 ml (21 to 27 fl. oz.) of sweat! Each hour you sweat out almost as much fluid as contained in one standard (about 24 oz.) water bottle!
If you push the pace a little, are climbing, are riding in hot weather or you are a larger rider, you could easily produce 32 fl. oz. (1 quart or liter) or more of sweat per hour.
Your personal sweat rate depends on your fitness, how hard you are riding, the ambient conditions and the variability among individuals.
Drink, don’t pour it on!
Heat-related problems — dehydration, nausea, heat exhaustion, etc. — are the result of an elevated core temperature. Your body is like a car’s radiator. Blood circulates through your core, heats up and circulates to the skin, where heat is dissipated via sweat.
If you pour a bottle of water on your skin, it will sure feel good, but it won’t help to maintain your core at a safe temperature. If it’s hot and you’re down to your last bottle, drink it, don’t pour it over your head!
Next Week: I’ll cover electrolytes, what you need and how to replace what you sweat out.