Cycling hydration: it’s not all about water and coffee

Hydration, energy, salt and food strategies for longer, harder rides

by our own Dr. David 


Water: am I drinking enough? Probably not…underwater-cycling

Roughly 60% of the human body is water, so to guarantee peak performance on the bike it is important to maintain the balance. During exercise your body loses water in the form of sweat (mainly), urine and water vapour through breathing (ask a dog!). Evaporation of sweat from the skin is the main way your body sheds heat. Without that cooling the increase in your core body temperature (from heat generated by your working muscles) would kill you fairly rapidly.

To determine your sweat rate, weigh yourself before and after a typical 1 hour ride without a drink (naked, dry with empty bladder before and after). Most riders will typically lose 500-1000 ml per hour.  If you’re at the upper end of this range, it might not be practical or necessary to try and replace it all but you should aim for a minimum of 75%.

Surprisingly small fluid losses can significantly affect your performance. A 2% drop in body weight due to sweating (1.6 kg for an 80 kg rider) will impair performance noticeably. Studies carried out in cool laboratory environments have shown a 5% decrease in VO2 max with a 3% decline in body weight through dehydration. At 5%, heat exhaustion can become an issue and your capacity for work will drop by up to 30%. Hit 7% and you’ll start experiencing hallucinations and, at 10%, circulatory collapse, heat stroke and even death become possibilities.

The physiological reasons for performance losses due to dehydration are:

  • Reduction in blood volume
  • Decreased skin blood flow
  • Decreased sweat rate
  • Decreased heat dissipation
  • Increased core temperature
  • Increased rate of muscle glycogen use
  • Decreased digestive function

So, what does all this mean I should do…?

In the hour leading up to a long ride sip 500-750 ml (one full bidon*) of fluid (* bidon = your water bottle)

Drink at least 500ml (one bidon) per hour on the bike. Don’t wait until you’re thirsty but drink but little and often right from the start of your ride. Aim to take 2-3 good sized gulps from your bottle every 10-15 minutes right from the moment you set off. You’re not drinking for that moment but to ensure your body stays properly hydrated 10-20 miles down the road.


During heavy exertion calorie consumption can range anywhere from 600 to 1500 kcal/hour. Energy consumption will vary depending on many factors e.g. the size of athlete, intensity of exercise, climatic conditions and level of fitness.

It has been shown that an average athlete can only readily absorb (process) between 200-600 kcal/h resulting in a negative energy balance. For longer rides, it makes sense to combine drinking with calorie intake. Remember, for a sportive or long training ride, you’re aiming for 0.5-1g of carbohydrates per kilogram of bodyweight per hour and should aim to spread that over 2-3 micro feeds every 20-30 minutes.

500 ml of typical sports drink mixed at 6% will give you 30 g of carbohydrate which, for an 80 kg rider requiring 40-80 g per hour, is a decent and easy to take on proportion of that energy requirement.

Energy gels generally contain 22-30g carbs which is 80-115 kcal. So 2-3 gels per hour will supply the maximum calories one can absorb but may cause nausea.

Maltodextrin is a non-sweet high GI sugar ideal for supplying energy during cycling. I’ll share more thoughts on the use of maltodextrin in my next blog along with recipes for making up some lower-cost energy drinks.


Much has been made about combining fructose with other high GI sugars e.g. glucose and maltodextrin in energy drinks and bars. One study suggested a benefit but this has not been substantiated. In fact fructose is much harder to digest and may slow stomach emptying and actually reduce energy absorption!

My simple advice to get the energy you need on the bike

  • Use both energy gels AND energy in your drink (don’t just carry water in your bidon) 

Ideas for consuming adequate energy during a longer ride: bike-overloaded
The following are examples of how to take on 60-80g of carbs per hour

  • 400 ml of energy drink mixed at 5% solution (35 grams) + one energy bar (35 grams) = 70 grams
  • 800 ml of energy drink at 6% solution = 70 grams
  • 3 energy gels (25 grams each) = 75g
  • 3 bananas (25 grams each) = 75g (you’d need a big pocket in your jersey!)

You can neither carry nor digest 10-12 bananas in one 3-4 hour ride….so, a mixture of the above options is possibly the best strategy e.g. two full bidons of energy mix, a banana or two, plus a handful of gels. Take a few electrolyte tablets then add them to your water when you refill the bidons at the half-way cafe stop.

Salts: when do I need them, and how should I get them?


Sodium concentration in sweat varies from person to person but is typically 1g/litre. Sodium loss will vary depending on many factors e.g. the size of athlete, intensity of exercise, climatic conditions and level of fitness. Sweat loss can be between 500ml – 1L per hour (500mg – 1000mg of sodium) – you can generally expect to lose more in summer, less in winter.

1 litre of sweat contains up to 1g of sodium (= 2.6g of table salt).

Table salt contains 387 mg/g. So 1 teaspoonful = 6g = 2300mg

Energy gels generally contain carbs plus sodium 10-40mg. So 2-3 gels per hour will supply the maximum calories one can absorb but not enough sodium (30-120mg).

Table salt, electrolyte tablets or food will be required to replace sodium loss. Electrolyte tablets typically supply 250 -360mg sodium.

My advice

  • Use both electrolyte tablets and carbohydrates in your water
  • Consider eating salty snacks on long rides


Magnesium: do I need it?

Magnesium seems to be “en vogue” with promises of increased performance and reducing cramp. While many studies on magnesium supplementation and exercise have been carried out, the results have been inconsistent and may indicate that there is nothing to be gained by supplementing an already magnesium-sufficient diet.  But for those already deficient in magnesium increasing magnesium in the diet may improve performance.

My advice

  • There is no hard evidence for consuming magnesium during exercise



The exact reason for cramping is still unknown. Many people blame inadequate hydration or electrolyte levels and, although some studies have shown that consuming a 6% carbohydrate sports drink can help prevent them. Regular training does improve the time before the onset of cramp.

My advice

  • Ensure adequate fluid and energy intake. Nothing beats regular training to help endurance!


Protein: can I digest it during a ride, or is it only for recovery?

During a long ride at high-intensity your body burns glucose from its glycogen stores (and digestion) as the preferred energy source. When this is depleted (mine lasts approx. 2 hours at anaerobic threshold) it will look to other sources of energy i.e. fat and protein. These both require a lot more oxygen to obtain the energy from the longer molecules.  Recent research on 10 trained cyclists performing an 80K trial showed that riders drinking carb-only did just as well as those drinking carb-protein drinks, and both groups did better than those consuming flavoured water!

If you’re on a long ride where you’re also eating, you’ll be taking in protein already so it’s unnecessary to also have protein in your drink.

My advice

  • Save protein for your recovery drink
  • There is nothing to be gained from consuming drinks containing protein during a ride


Fats and fibre

The pies and sausage rolls in the farm shop may look like a good source of energy when you are feeling the hunger pangs after riding over the North Downs but they take a long time to digest and will actually slow down the absorption of the carbs you need to get you home. The same applies to fruit and muesli bars.

My advice

  • No meat pies. A jam sandwich would be better
  • Not too many bananas


Caffeine: to caffeinate, or not to caffeinate, that is the questioncoffee-beans

Caffeine improves carb burning. Researchers found that riders who drank a caffeinated sports beverage burned the drink’s carbs 26 percent faster than those who consumed a non-caffeinated sports drink, likely because caffeine speeds glucose absorption in the intestine.

Also worth noting that the stimulant doesn’t worsen the effects of summertime heat. In fact, caffeine makes you feel better. Numerous studies have shown that it lowers your rate of perceived exertion while improving your strength, endurance and mental performance.

My advice

  • Drink coffee!
  • Stop for coffee!

My next blog will be a recipe for making your own cost-effective cycling drinks using maltodextrin.

Enjoy your cycling

Some links if you wish to read more on the topic


Disclaimer: Please note the information in this article has been researched in good faith or from my experience and is for guidance only and not medical advice.

David Matthews – Nov 2016