At the Tour de France, riders will drink three or four bottles every hour to keep their fluid stores topped up and avoid performance declines from dehydration.

Even a two percent loss of bodyweight due to fluid loss will significantly impair strength, power, and endurance. Fluid loss reduces blood plasma volume, which forces your heart to beat faster to send oxygen to your muscles. Dehydration also impairs your body’s ability to sweat, which is its principal mechanism for thermoregulation. When your body can’t cool itself, your core temperature rises, which soon results in drastic performance declines. Reaction times and concentration drop, so you will make worse in-race decisions. 

To avoid dehydration and keep our riders performing at their best, soigneurs race around the course of every stage with cold bidons of water and Amacx drink packed with electrolytes and carbs. To give our riders the chance to win, we need to keep them hydrated.

A complicating factor is the fact that riders’ sweat rates and sodium loss rates differ significantly. This is true of every athlete. Most recommendations for fluid and electrolyte intake are based on averages and will only get you so far. 

“Muscles are mostly water, so maintaining hydration means maintaining the tissue that produces movement, power, and performance,” EF Pro Cycling Head of Nutrition Dr. Anna Carceller says. “When hydration is individualized, it becomes one of the most powerful tools to support performance.”

To know how much you should consume at different temperatures, you need to test your sweat rate. There are two principal factors to consider when you are measuring your own sweat rate. First: overall fluid loss. Second: sodium losses. Both can differ substantially between athletes. To measure fluid loss, weigh yourself before and after exercise. One kilogram of weight lost equals one liter of sweat. Just remember to account for what you drink. If, for instance, you are one kilogram lighter at the end of your ride and drank two 500-milliliter bottles, you lost two liters of sweat. You want to conduct tests at various temperatures and exercise intensities to understand how your body sweats. Track this to inform how much you should drink. 

Sodium losses are trickier to measure. Commercial analyzers measure the sodium concentration of sweat collected in patches that you place on various parts of your body. This is the most practical way to understand how salty your sweat is. Once you know your sweat rate and sodium loss rate, you will be better able to understand how much fluid you need to drink on the bike and the quantity of electrolytes you should take in different conditions.

"Fluid intake and sodium intake need to be considered together," Anna says. "What matters is how you replenish losses: if you're replenishing more than about 70 percent of fluid losses with water, that's when you should start thinking about sodium. If you're not hitting 70 percent replenishment, don't add sodium yet. Think of the body as a system where sodium is diluted in water. Sweating concentrates that solution – you lose more water than sodium, relatively speaking. If you add sodium without enough water, you over-concentrate your body's fluids further, which is counterintuitive but important to understand. 

“So the sequence is: first replenish water losses, then add sodium to that replenishment so the overall solution has the right water-to-sodium ratio. Taking sodium without enough water is a common mistake. If you can't measure the sodium content of your sweat, aim for 500 milligrams to 1 gram of sodium per liter of water replenished. It's also worth noting: for hydration purposes, drinks need to be water or isotonic. Hypertonic drinks – more than 30g of carbs per half-liter – do not hydrate."

Amacx Energy drink contains 372 mg sodium per 30-g-of-carbohydrates serving. That means that two 500ml bidons of Amacx Energy per hour will be sufficient for most riders. You should aim to replenish about 60 percent of the sodium you lose every hour. Very salty sweaters can supplement their sodium intake for long, hot rides using Amacx Hydrotabs, which contain 205mg of sodium per tab.

If you get the balance right, you’ll be able to ride at your best from the start to the finish of the hardest rides, like Richard Carapaz did when he attacked up Orcières-Merlette to win Stage 18 of the Tour de France and Stage 20 up Alpe d’Huez.