Get the drinks in… Cycling Hydration Strategy Explained


14.11.19 at 11:12 am

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‘Drink plenty of water’ is an adage that goes a long way in endurance sports, in most sports really, even for civilians engaged in office or home sports. Problem is, as advice goes, it’s pretty general and under the extreme duress of endurance sports, it could… Excuse the pun, land you in performance-plunging hot water.

For starters, very few cyclists, triathletes and long-distance runners drink just water. Rather it is which kind of performance fluid at which dilution and which standard absorption rate in the gut? And how much does water in food inputs count?

How do these factors change over the many hours of an endurance event? And how much does the heat and humidity of the day or night change things? And what about hyponatremia (drinking too much)? And what are the early warning signs of a hydration crisis in training or during an event? Read on liquid lords…

cyclist drinking energy drink - Cycling hydration

Ultra-distance bike racer and 2019 Paris-Brest-Paris finisher Darren Franks knows a thing or two about the hydration equation. “Unfortunately hydration isn’t as simple as ‘500ml/hour’ or even ‘drink to thirst’,” he tells The Draft.

“Needs will vary according to the intensity and duration of the effort, the climate and your own individual physiology. Alongside fluid losses, it’s important to consider electrolyte balance too, which can be too high as well as too low.”

For most folk, scientific consensus shows 1-2% of body weight can be lost before euhydration (a normal level of hydration) is compromised and performance likely to be impacted.

“It’s quite common for me to finish my longer rides (200km+) up to 2kg lighter,” observes 40-year-old Franks, who has completed the two doyens of ultra-distance racing: the 6800km TransAmerica and the 3000-4000km Transcontinental in Europe.

“I should be aiming to keep that to 1.5kg but you’re judging it by feel when you’re on the bike and it’s a gradual process to train myself to drink fractionally more.”

Laying waste to the best Cycling hydration plans…

Franks himself recently lost about 5kg in a 6-hour stint at the Revolve24 event at the Brands Hatch motor racing track in England. “It was enough to negatively impact performance,” recalls Franks. “Sure enough I suffered debilitating cramps in the final two hours of the race, forcing me to tread very lightly on the pedals.”

For an experienced ultra-distance racer like Franks, the weight loss and hydration issue was surprising but he put it down to the high intensity, Time Trial-style effort where he hit a pretty insane 90% of his Functional Threshold Power for the first four hours: “There were no lulls in intensity like you’d find on a road race or a long training ride. As a result, my sweat rate was quite a bit higher and I’d not adequately factored this into my hydration plan for the race, which was very optimistic as a result.”

The Londoner, enduro-warrior that he is, still managed to podium in the event he had twice won.

‘Cumulative effects of slight mismatches between fluid needs and replacement’

The issues experienced by Franks are not uncommon – there are simply too many variables involved to make optimum hydration anything like an exact science. The American College of Sports Medicine (ACSM) acknowledged as much, especially for prolonged exercise lasting greater than 3 h”, in a 2007 position paper on hydration.

“The longer the exercise duration the greater the cumulative effects of slight mismatches between fluid needs and replacement, which can cause excessive dehydration or dilutional hyponatremia.”

ACSM added: It is difficult to recommend a specific fluid and electrolyte replacement schedule because of different exercise tasks (metabolic requirements, duration, clothing, equipment), weather conditions, and other factors (e.g., genetic predisposition, heat acclimatization and training status) influencing a person`s sweating rate and sweat electrolyte concentrations.”

Others like the US Institute of Medicine (IOM) have laid down some guidelines for endurance athletes in hot weather. It recommends 20–30 milliequivalents per litre (meq/L) of sodium chloride and 2–5 meq/L of potassium and between 5–10% carbohydrate dilution.

The IOM notes gels, bars and other foods can also be sources of these nutrients.

The ACSM highlights several other factors that can explain differences between hydration rates in individuals including:

  • Older adults have decreased thirst sensitivity and are therefore slower to re-establish euhydration
  • Women sweat less than men and are more prone to hyponatremia
  • Children sweat less than adults

Contrary to how it is perceived by many, the ACSM says caffeine “will not markedly alter daily urine output or hydration status.”

Carbo load…of bollocks?

Hydration issues can be exacerbated by carbohydrate and liquid-loading, which despite largely falling out of favour among sports nutritionists, remain popular among endurance athletes before big efforts and events.

Click here for Ironman Nutrition Plan Tips

Jeff Sankoff, Ironman racer, licensed physician, ex-medical editor at Inside Triathlon and Triathlete magazines and founder of TriDocCoaching, baulks at hearing of athletes in such dire straits.

“I am particularly put off by the continued recommendations to ‘hyper hydrate’ or load with carbs in the days before the race,” he says.

“It simply defies physiology and is supported by no scientific evidence whatsoever. Our kidneys will simply remove all of the supplemented electrolytes and fluids – it’s money down the toilet.”

The ACSM says, “Prehydrating with beverages, if needed, should be initiated at least several hours before the exercise task to enable fluid absorption and allow urine output to return toward normal levels,” adding “salted snacks or small meals with beverages can help stimulate thirst and retain needed fluids.”

Getting past gastric upset

One of the big conundrums of sports nutrition is the trade-off between your body’s hydration and energy needs, and the effect nutrient-loaded fluids can have on gut function during endurance events.

“If both fluid replacement and carbohydrate delivery are going to be met with a single beverage, the carbohydrate concentration should not exceed 8%, or even be slightly less, as highly concentrated carbohydrate beverages reduce gastric emptying,” the ACSM states.

For Jeff Sankoff most gastrointestinal distress for endurance athletes is a result of delayed gastric emptying and increased gut water caused by “simple sugars pulling water into the gut”.

“This can deteriorate very quickly if athletes aren’t prudent.”

If an athlete notices GI distress, nausea or a sloshing feeling in the stomach, Sankoff recommends reducing effort level by 10% and “drinking and nourishing continuously in small quantities.”

Things to consider in order to perfect your hydration

Sankoff says “Decreasing the effort is the only way to allow for improved blood flow to the gut and improve gastric emptying and absorption from the small intestine. Once symptoms improve, begin fuelling and hydrating normally and then increase the effort if tolerated.”


Read more about Darren Franks’ ultra-distance cycling adventures here.

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