Here’s how dehydrated you really become after working out
The weather doesn’t have to be warm for you to become dehydrated – an hour’s run or gym class will use enough bodily fluid to send you into the red. Here’s why drinking during your workout is better than trying to refuel after exercising.
Sweating during your workout is undeniably a good thing, as is drinking plenty of water throughout the day. But how many of us know how much we should be drinking to replenish our stores post-workout?
If you’re anything like me, drinking on a run is a rarity. I get you might not want to carry the stuff, but we’re doing ourselves a massive disservice by not drinking during workouts.
Why drinking during exercise is better than rehydrating after working out
A 2010 study from the Journal of Exercise Science & Fitness confirms that “performance decreases after prolonged exercise without fluid intake, and that fluid ingested during sport activities could prevent the decrease in balance performance”.
That suggests then that if you’re training for a half marathon, for example, you should be training with water throughout your runs – taking small sips as and when – rather than looking to replace lost fluid at the end. If you drink enough during your workouts (whether that’s a 45-minute strength class at the gym or an hour’s jog), there shouldn’t be a massive difference in body fluid before and after.
One of the reasons that humans are thought to be ‘born to run’ is that we sweat. We’re one of the only animals on earth who have this internal cooling system that stops us from internally combusting while on the move. If we didn’t sweat, we’d keel over after 5km; because we can secrete fluid to cool our skin down, we’re able to run marathons, cycle ultramarathons and lift heavy weights.
Sweating is necessary but if you don’t replace all that liquid, you end up feeling groggy, tired, slow – and worse.
How to workout how much fluid you’ve lost during exercise
Generally speaking, you’re supposed to drink one and a half times the fluid you lost while exercising – spread over two-to-six hours post-workout. Drinking a glut of water immediately after working out may not be a great move if you want to avoid bloating (thanks to the fact that our bodies are in a state of inflammation after a heavy session).
To work out exactly how much fluid you’ve lost, you’ll need a pair of scales. Obviously, if weighing yourself is going to be triggering, just listen to your body and drink as much fluid as feels right (erring on more rather than less). If you’re OK with weighing yourself, purely for scientific purposes, however, then you could use this “sweat rate calculation”:
- Weigh yourself naked before your workout, post-loo
- After your workout, get naked, go to the loo and weigh yourself again
- Convert the difference into grams
- Multiply that number by 1.5
- For every kilogram of weight lost over the course of your workout, you need to drink 1.5 litres of water.
So, let’s take Mia as an example. Mia’s just come back from an hour’s jog.
Before her run, Mia weighed 64kg (naked and after having a pee)
She now weighs 62.3kg, following her run (again, having used the loo and stripped)
6400-6230 = 170 x 1.5 = 255
Mia lost 170g during the course of her run and now needs to take on 2.5l of water over the course of the next few hours.
An arguably easier and less triggering way to work out how much you’ve lost is to look at the colour of your pee. If your urine is a deep yellow, you need to drink some water ASAP; if it’s pale, you could probably do with a glass or two; if it’s almost colourless, you’re all topped up.
An hour’s workout is long enough to become dehydrated
It doesn’t have to be hot for you to become dehydrated. In fact, just one hour of exercise can cause us to lose more than a quarter of our body’s water – putting us at risk of muscle fatigue and poor coordination.
Rehydrating during workouts can help to prevent a decline in performance, strength and aerobic capacity. Ever been on a run and felt low energy or felt slower in your reaction times? There’s a reason for that: dehydration.
One study, published in the Journal of Nutrition, concluded that drinking during longer events was preferable to drinking before or after training and competition only. “Athletes seldom replace fluids fully due to sweat loss,” it said.
“Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss.” Doing so also avoids issues of over-hydrating before or after an event which can happen when we’re desperate to take on fluids – leading to stomach issues and further depleted mineral reserves.
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When to drink during your workout
Working out when to drink during your workout is the next hurdle.
A 2016 study from the Journal of Sport and Exercise Sciences, looked at how dehydration impacted certain cognitive processes. Scientists got 20 students to do an hour of treadmill running, with the majority continuing until they felt too tired to run.
Every 15 minutes, they were instructed to drink 225ml water and then once they’d run for the hour, they were then able to drink according to thirst rather than dictated timings. Scientists found that exercise performance was significantly better when the runners were able to choose when to drink, rather than having to take on water.
The conclusion? Knowing when you need a drink is far preferable to forcing yourself to drink or waiting until you’re already in desperate need of water post-workout.
How to stay hydrated while exercising
Take water with you
If you’re at the gym, take a full bottle of water in with you and be sure to drink as and when you feel thirsty. Most class instructors will give you a cue to drink; you don’t have to take advantage of that break but it’s worth assessing if you need a sip then or not.
Under 10k, you probably don’t need to take water with you on a run, but if you’re running fast or for more than an hour, take a hydration vest or water belt with you on your runs. Again, sip as and when you feel the need. After you’ve run for an hour, maybe set yourself an aim to have a sip every 20 minutes or at least think about whether you need a drink every 5km.
Add electrolytes to your drinks
Studies have revealed that rehydration after exercise can be achieved only if water and electrolyte losses are replaced. “Replenishing your water and electrolytes losses after training is important for recovery, particularly when you engage in exercise lasting longer than two hours, or in vigorous exercise for an hour or longer,” Alex Ruani, UCL doctoral researcher and chief science educator at The Health Sciences Academy, previously told Stylist.
Keep drinking after you stop moving
Even if you do drink during your workout, it’s still a good idea to make hydration a priority in the hours following. Set a timer to remember to drink once you’ve finished your heavy workout or run for the next few hours. Don’t try to drink lots of fluid all at once but set yourself a reminder to have a glass of water every 30-45 minutes.
For more nutritional tips, workout plans and how-to videos, visit the Strong Women Training Club.
Images: Getty
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