Earn while you burn: I went running for digital currency

Look, I know you're probably sick to death of hearing about Bitcoin by now, but what if I told you that there's a digital currency that can be earned just by putting one foot in front of the other? And no, this isn't a pitch for Black Mirror.

Sweatcoin's been kicking around the idea of the "movement economy" since 2015, but it's been stirring up more attention as of late in the wake of cryptocurrencies like Bitcoin gaining traction. Sweatcoin has more than 2 million weekly active users, and what's more the company just got a $5.7 million injection in seed money.

Sweatcoin has also bragged about its meteoric rise in the app store, overtaking major fitness rivals like Fitbit and Garmin, and as of writing it's sat at number 2 in the iOS free app chart.

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Here's the basics of how it works: the app tracks steps taken outdoors on the Apple Watch (or just the phone if you'd prefer) and converts that into its unique currency of Sweatcoins. It does this through a combination of GPS (so you'll need the Series 2 at least if you're just using the watch) and a pedometer. That's because only steps taken outdoors will count. On the down side, this means your treadmills have no monetary value. Plus side: it works for cycling.

1,000 steps will earn you 0.95 Sweatcoins (technically it's a whole coin, but Sweatcoin takes a 5% commission), which is an average conversion rate of about 1km to 1 Sweatcoin, give or take a little. So I put it to the test: I installed the app on my Apple Watch, threw on my running shoes and headed out the door, hoping to return a very rich man. A tap on the screen told the app I was starting a workout and it began racking up those steps and miles, which are handily displayed in real time during exercise, so I didn't need to boot up a second app to track my run.

At the end of my 5K run I stopped the app, which told me I'd earned myself 5 Sweatcoins. Oh, and a bonus coin for just logging in. The currency gods were smiling down on me. I'd probably have to tell my bosses I won't be coming in tomorrow. I'd phone them later - from my bath of money.

But then came the catch. Well, a cap. A red cross appeared on my Apple Watch screen to signify that I had hit my ceiling of 5 coins per day. Which meant that if I were to try and get, say, the $93 Vici London watch gift card, priced 430 Sweatcoins, it would take me almost three months of maxing out my daily allowance.

That's... maybe not terrible. However, you can raise the daily cap by upgrading to a paid subscription. The maximum right now is the Breaker subscription, which costs 30 Sweatcoins a month and raises the daily cap to 20 coins - or a monthly net maximum of 570 Sweatcoins. Some quick back-of-the-napkin maths tells me I'd need to hit my daily limit on this tier for about three years to earn the 55-inch Samsung curved TV, priced at 20,000 Sweatcoins. Though I could afford a Fitbit Flex 2 within a month! Not bad.

Smaller rewards include music downloads and short-term subscriptions to services. But they do climb pretty high too. There was even a $1,000 Delta flight gift card available at one point.

But that's not the most interesting part of this. Sweatcoin's creators actually want to get Sweatcoin trading on the digital marketplace alongside Bitcoin and other cryptocurrencies. That would give Sweatcoin more of a discernable value. For the time being, beyond the store itself, some users are selling Sweatcoin for PayPal money and other things, but the exchange rates are all over the place.

So is there longevity in this idea of running for currency? Is the "movement economy" a thing? Fitcoin, a similar idea that worked with Jawbone, Mio and Atlas wearables, didn't quite stick, but I do think Sweatcoin might have cracked it, and I'll certainly keep using the app in my workouts.

But if this economy is really set to boom, I'd rather not buy anything and instead hold onto most, if not every coin I earn. Who knows, perhaps one day soon Sweatcoins will be tradeable for real, hard cash. If Garmin, Fitbit and, well, just about every other fitness company thought the Bitcoin bonanza was nothing to do with them, they might want to think again.