Learning from the Pros: Heat and Hydration

By Coach John Hughes

In the 2018 Tour de France, which culminated with the climb of L’Alpe d’Huez, it was 28C (82F) in valleys and 21C (70F) on top of climbs. The stage featured two Hors Catégorie climbs, each over 2,000 meters (6,500 ft.), before the finish on L’Alpe d’Huez at 1,950 meters (6,060 ft.). About the earlier climbs the Cycling News live blog commentator said, “It is so warm today that capes and gilets (vest with windproof front and mesh back) are not needed.”

Although the ambient temperature wasn’t that high, heat was an issue.

Why Racers Get Hot

The racers overheat in several different ways and understanding these will help you perform better in the heat:

1. Energy production. The human body is only 20 to 40% efficient, which means that only 20 to 40% of the energy that a racer gets from eating is translated into forward motion — the rest becomes heat. The racer has to dissipate this heat or the core temperature will rise. Energy production and heat dissipation are the primary factors in overheating.
2. Radiation. When the sun is out, the peloton gains heat from direct radiation as well as from radiation reflected from the pavement. They may also gain heat from radiation through diffuse clouds. The higher the sun is in the sky the more radiation heats a rider up. Because the stages start in the early afternoon the peloton is exposed to maximum radiation.
3. Respiration. If it’s really hot the racer may gain heat through breathing. Hot air feels harder to breathe.
4. Conduction. The rider also gains heat through hot parts of the bike.
5. Convection. If the air is hotter than a racer’s body, the body absorbs heat.

Note that convection is the result of high ambient temperature, and during the L’Alpe d’Huez stage the air temperature was lower than the skin temperature and this one wasn’t a cause. The other four causes of getting hot are independent of the air temperature. Even though the ambient temperature wasn’t extreme, with all the climbing controlling a racer’s core temperature was critical.

Increasing the racer’s sweat rate and radiation from increased blood flow to the skin account for about 85% of the body’s cooling. The rest comes from conduction and convection. Because sweat rate is so important adequate hydration is key.

Hydration

A racer can only absorb so much fluid per hour. Different studies report maximal rates of intestinal fluid absorption ranging from 600 ml (20 fl. oz.) to 1.6 liters (54 fl. oz.) per hour. When climbing hard a racer could easily sweat out two liters per hour, more than the racer can drink!

Geraint Thomas (GBr) Team Sky won the L’Alpe d’Huez stage in 5:18:37. During the stage, the racers drank about two 0.5 L (16 fl. oz. bottles) per hour.

Glycogen is the primary fuel during a race. A racer can store about 450 grams of glycogen. For each gram of glycogen the body also stores three grams of water for a total of about 1.35 L of water. During a race the riders are eating primarily carbohydrates to provide glycogen (see my column on Learning from the Pros: Cycling Nutrition); however, they are also drawing on their glycogen stores, which provides additional hydration.

The racers’ fluid consumption supplemented with stored water was less than they sweated out so they got dehydrated. A rider is not allowed a feed from the team car in the last 20 km of a race. This is to keep the cars and riders apart when white line fever has kicked in. This increases dehydration.

Does Dehydration Matter?

The American College of Sports Medicine (ACSM) recommends drinking enough during exercise to prevent excessive dehydration (>2% body weight). Dehydration is expressed as a percentage of body weight. If a 160-lb (73 kg) rider loses more than 3.2 lbs (1.5 kg) during the course of a ride, the cyclist is more than 2% dehydrated.

If dehydration inhibits performance then as the day wears on the riders would slow down and sprints for king of the mountain points and flat out sprints at the finish would be impossible. Clearly dehydration doesn’t affect their performance!

Over-Hydration Is Dangerous

The ACSM also recommends not drinking so much fluid that excessive changes in electrolyte balance result. Too much fluid can dilute the blood sodium level to a dangerously low level (hyponatremia). The sodium concentration in electrolyte drinks is less than the sodium concentration in the blood so drinking too much of a sports drink can also cause hyponatremia. Hyponatremia can cause the body to retain fluid, which causes bloating. As the rest of the body bloats up the brain also tries to swell; however, it can’t because of the skull. The increasing pressure on the brain can be fatal. If you notice swelling around the top of your socks or your gloves or a ring on a finger you are retaining fluid. Stop drinking until the swelling goes down!

What Do Racers Drink?

Depending on preferences and stomach issues, a racer drinks water, sports drink and Coke. Most teams use a commercial sports drink. A few outsource custom drink mixes and have them tested for purity to be sure they won’t present problems with drug testing.

Recovery

Drinking and eating right after the riders get off the bike is essential for recovery for the next day. Each racer is weighed before and after a stage. For every kilogram lost a racer has lost one liter of fluid. The racer drinks 1.5 L. per kg. of lost body weight. The rider drinks this much both to rehydrate from the stage and to meet ongoing fluid needs.

Bottom Line For You

• Drink enough daily that you stay hydrated. The old maxim of “drink eight glasses of water a day” doesn’t apply. Fluid needs differ by body size, age and the temperature depending on the season and where you live. Drink enough that you pee with a good clear stream of urine every few hours.
• On a ride drink enough to satisfy your thirst but don’t overdrink; however, the sensation of thirst diminishes with age.
• Drink what you like. There are no performance enhancing drinks – if there were they’d be banned by the World Anti-Doping Agency. There’s a recipe for a homemade sports drink on my website that many of my clients like.
• After a ride rehydrate adequately by drinking enough that you urinate with a good clear stream. Drinks with carbs are better than plain water; however, if you prefer water also eat some carbs. There are no magic recovery drinks.

Cycling in the Heat Bundle

You can learn more about the science of riding in the heat, and managing your fluids and electrolytes, in my two-part eArticle:

1. 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.
2. 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.

The cost-saving bundled eArticles totaling 40 pages Cycling in the Heat Parts 1 and 2 are just $8.98 (a 10% savings) and, as always, just $7.64 for our Premium Members (includes their everyday 15% discount!).

Summer Bundle

The summer bundle includes:

• Cycling in the Heat, Part 1: Ride Management, 19 pages
• Cycling in the Heat, Part 2: Hydration Management, 21 pages
• Preventing and Treating Cramps, 10 pages
  A detailed look into the causes of cramps, prevention techniques, and tips (both on-bike and off-bike, including photos) for breaking and flushing cramps.
• Eating and Drinking Like the Pros, 15 pages
  What pro riders consume before, during and after a stage and the 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 at a fraction of the cost of commercial sports food and drink, if you choose to make our 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.

The cost-saving bundled 65 pages of eArticles Summer Riding are just $15.96 (a $4 savings) and just $13.58 for our Premium Members when they use the premium member discount code.

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Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.