Drinking during exercise: Drinking to thirst or drinking to plan?

News and Updates

by Chloe McLeod

When working with athletes of any type, but particularly with triathletes, managing hydration is often considered to be one of the more confusing aspects of getting the race right.

Whilst there’s plenty of people recommending to drink when thirsty, there is also plenty who state that a specific plan in place is required.

So, to drink to thirst or drink to plan?

What we do know is that most athletes don’t rehydrate well enough during their events or training, with most usually not consuming adequate quantities to remain hydrated enough.

Whilst it may sound like I’m being a fence sitter, hear me out when I say ‘I suggest both’.

When I’m working with a client individually, I’ll always ask how much they usually consume before/during/after their training sessions. Based on this, we will develop a plan.

This is done by weighing before a training session holding bottles of water/sports drink they plan on consuming during the session. After the session is done, jump back on the scales, again with their (likely now empty) water bottles. This allows you to check sweat volume. Sweat rate is the volume divided by time.

Whatever the difference is, this is what is required to rehydrate afterwards, times 150%. Ie, if you’ve lost 1kg, rehydrating with 1.5L of fluid over the next 3-4hrs is suggested.

So that’s after, what about during?

If the sweat rate shows more than 2% loss of body weight, performance is very likely to be inhibited. Even 1% can result in poorer performance. As such, more liquid needs to be consumed during the session, and this is where development of a hydration plan comes in. Research indicates that drinking to match sweat losses, or at least minimising to 1% does provide a performance advantage.

What to drink?

Water, sports drink and/or electrolyte drinks are my go to recommendations. Mixing these up throughout the event will help reduce flavour fatigue, to help you feel better as well. Sipping as you go, or drinking regularly is suggested, as smaller amounts on a regular basis will hydrate better than a large quantity of fluid all at once.

When to deviate from the plan

Whilst having a plan is obviously helpful, there are so many other things that come into play than simply relying on how much you sweat on a given day. Race day conditions will impact how much your body needs; as an example, if your hydration plan is based on sweat rate from a mild temperature day with a few clouds in the sky, but race day is either cold, windy, rainy, or the other extreme of sunny, hot, dry, or some other variation from when your sweat rate was tested, you are likely to require more or less fluid than the plan describes. This is where drinking to thirst comes in.

Take home?

Do a session on the bike or in your favourite runners for an hour, during likely race day conditions, weighing in minimal clothing before and after. Have a look at the difference, then plan your hydration from there. Keep in mind other potential factors that may influence hydration on the day of the race, or on other training days.

Chloe McLeod has had a keen interest in nutrition from a young age due to food intolerances as well as a realization about the important role food plays in an active lifestyle. She has a bachelor’s degree in Nutrition & Dietetics, a master’s degree in Public Health, has received Sports Dietetics training through the Australian Institute of Sport, and has earned qualifications for ISAK Level 1, and is a member of DAA, SDA, and PINES. She is a two-time marathoner, avid trail runner, and also enjoys staying active through snowboarding and Pilates.


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