This summer has been hot. At times - really hot!
As welcome as this long overdue summer might be, I know a lot of runners, trekkers (and cyclists) are struggling in the heat and are understandably unsure how best to train or race with the mercury well in the red zone.
Social media posts are crammed with “drink plenty of water” advice—but is it really that simple?
Just drink more and—hey presto!—you’re immune to the sun and the effects of heat when training?
Of course not. And here’s why.......
Humans are essentially big hairy bags of water—but it’s not just about how much water we have, it’s about where it is, how quickly it’s shifting, and how efficiently we use it.
Water makes up 50–70% of our total body weight (closer to 70% if you're lean and muscular). But this fluid is constantly on the move.
We lose around 2.5 litres of water per day just through breathing, sweating, peeing, and the odd emergency sprint for a bus. Add a training session in 28°C and you could easily double that loss.
And don’t assume all that water 'lives" in the same place.
About 60–70% of it is inside your cells (intracellular fluid), while the rest floats around your bloodstream and spaces between cells (extracellular fluid). The body constantly juggles these compartments to keep vital systems running—like a biological water butler, deciding who gets a top-up and who can wait.
The bummer? Just a nominal 2% drop in total body water can impair cognitive function and athletic performance. At 4%, we’re into true dehydration territory: reduced endurance, overheating, increased heart rate, and a higher risk of cramping and heat-related illnesses.
Saying “drink more water” is like saying “just run faster” to get a PB. It might work... or it might backfire.
Case in point—here are two of our recent body composition scans performed at one of our marathon training days:
A couple of glasses of water (about 500ml) is 1.7% of her body water, but less than 1% for him. The advice sounds the same but the physiological effect is wildly different.
This is why hydration is not one-size-fits-all. Your hydration needs depend on:
If you are unable to attend one of our training days and / or do not have access to a Bodystat machine, then try these hacks to find out if you need to up hydration game:
Training in heat doesn’t just make you feel more tired—it increases the physiological cost of every mile.
Start a session dehydrated and you’ll:
In fact, dehydration of just 2% of body weight has been shown to significantly reduce endurance performance and increase perceived effortHydration.
It’s worth mentioning: more is not always better.
Overhydration can dilute sodium levels in your blood, leading to hyponatremia—a potentially fatal condition.
This is especially risky for slower runners in long races, those on low-sodium diets, or anyone who overdoes it with water out of fear of dehydration.
The advice? Drink to thirst and comfort. If your stomach’s sloshing or you’re forcing it down—back off.
You can also consider popping in an electrolyte table into your water bottle - but careful not to go overboard.
So yes, it’s hot. But with a little planning, you don’t need to melt.
Drink smart. Train smart. And remember: you’re not just a big hairy bag of water… you’re a performance-tuned, fluid-balancing, heat-beating machine. 😂
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