How Much Sweat Do You Lose Running at Night in Malaysia

I noticed I get significantly sweatier when I run in the Malaysian heat, often looking like I ran through a tropical thunderstorm by the end of my runs. I wanted to find out exactly how much sweat do you actually lose running in Malaysia, so I did a simple experiment.

The Setup

The test was simple - I would weigh myself before and after the run. A simple 5km run at Zone 4 pace. No liquid intake in between. No pee breaks. The weight I lost should mostly be fluid through sweat.

And I was surprised.

I did the experiment with my brother to see the variance in sweat loss. He is also a little fitter than me and tends to sweat less.

Before the run, I weighed 76.7kg, while my brother, Justin, weighed in at 66.7kg. We did the run at night, so the weather was actually relatively cooler by Malaysian standards at ~28° C (that's "Upgrade-To-Metric" Degrees in Fahrenheit). It actually took me a while before I felt myself break first sweat around the 0.5km mark.

Justin and I both did the same 5km route. I clocked in it at 29:01, while Justin finished it in 28:24 mins. Definitely faster times than when we stupidly ran a 5k round a see-saw and I was late to pick my wife up. I also definitely looked the sweatier of the two of us.

So, what were the results?

I stripped off my sweaty shirt and weighed myself, coming in at 76.0kg. That was a -700g sweat loss. Justin weighed in after the run at 66.2kg, amounting to -500g in sweat loss. And this was a relatively short run on a cool Malaysian night! I was also surprised at the difference in weight loss between us, even if you convert it to % body weight loss.

	5k Pace	Weight Before	Weight After	Weight Loss
Bryan	29:01	76.7kg	76.0kg	0.7kg
Justin	28:24	66.7kg	66.2kg	0.5kg

Now, some of the weight loss was probably just from breathing out and being alive, but the majority of the weight was due to sweat loss and the electrolytes in the sweat. That comes out to around 500g of water, 500mg Sodium, 15mg Potassium, and 4mg Magnesium.

Takeaways

So, the 2 takeaways I had from this simple experiment:

1. You actually do lose a lot of weight through sweat running in Malaysia.

2. The sweat rate does vary quite significantly between individuals.

If you're a sweaty individual like me (literally), then be sure you are replenishing fluid loss on your runs with enough water, but also with the right electrolyte amounts and ratios. I'm biased, but that's exactly what we designed PUSH Rehydration Salts to do. Nothing better than a cold electrolyte drink after a run!