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Is the Strava calorie count reliable?

Ryan Georgiades | 6 months ago

I am currently 1.81m and 102kg, (can you tell which one I am from the photo) and I’d like to shed a few pounds and return to ‘race weight’. And there’s only one sure-fire way to do that according to the NHS: “To lose weight you need to burn more calories than you consume.”  So to this end I am logging what I burn using Strava and keeping a lid on what I consume by logging everything on MyFitnessPal.

That’s easier said than done (as I look at the doughnuts being offered around the office). But at least I’m running regularly (and cycling occasionally). And that means I can use my Garmin and upload my activity to Strava to see how many calories are being blasted away and how I’m doing against my peers. It’s a huge motivation: seeing the calories incinerated as I plod the streets in my Asics  or cycle up Boxhill, is a lot more enjoyable and inspiring than avoiding one of those doughnuts, or foregoing a mid-morning latte.

At least it used to be. Now I am exercising regularly again and consciously looking at the data I get, I’ve found that Strava’s calorie counts seem way too high. Below are the stats from three recent runs. As you can see, my Garmin and Strava seem to be almost perfectly aligned until it gets to the calorie column.  Strava seems to be throwing up figures between 10% and 19% higher than Garmin. At the top end we’re talking about the occasional doughnut (and of course the weight loss I’m aiming for!).

Distance (km) Time (mins) Pace mins/km Calories
RUN 1 Strava 9.50 51:36 5:25 1,177
Garmin 9.54 51:37 5:25 992
RUN 2 Strava 4.90 25:55 5:16 606
Garmin 4.92 25:53 5:16 541
RUN 3 Strava 9.50 52:45 5:31 1,178
Garmin 9.56 52:45 5:31 1,069

I decided to look into it a little bit more, and I’m not the only one that’s been left puzzled by Strava’s figures.

“Strava overestimated my calories by a multiple of over five. Yes, over five times what I actually burned,” noted Jason King on this support stream I came across on Strava’s US site.

And it seems that it works both ways, too. On the same stream, Rebecca Bee wrote: “It seems like Strava underestimates my calories burned.”

Rebecca explained: “I rode for one hour last night at an average speed of 11 miles per hour. It said that I burned 180 calories. My problem with this is that I could sit at my desk all day and burn 122 calories per hour. If I stand, rather than sit, I go up to 163 burned per hour.” What’s the point of all that effort for 17 calories an hour?

That stream of complaints started in July 2016 and is still going strong now. “Strava is about 30% high, making it useless for weight management,” said Strava user Dan Grey.

Dan offers a (conspiratorial) theory, too: “Strava likely inflated calorie consumption to attract users. Now, if they corrected their formula, there’d be a huge backlash. Better to put one’s head in the sand.”

So I asked Strava: what’s going on? And their friendly PR team referred me to the details posted on their public support page, dated February 7, 2012.

This basically says that the calculations are estimates and the differences you can get between tools are down to the algorithms used. “We believe our estimation is as accurate as possible given the limitations in data.”

Do experts think the same?

Dr Howard Hurst, a senior lecturer in sport, exercise and nutrition sciences at the University of Central Lancashire, told me that as far as he can work out, “Strava has a margin of error somewhere between 25 and 50%”.

His thinking goes like this:

“Strava determines calorie expenditure from speed and time elevation alone. The problem with this [is that] it does not take into account how hard you are working. For example, it has no way of knowing you were riding at 15 mph because it was a recovery ride or because you were riding into a headwind. Similarly it can’t distinguish between a 25mph time trial or 25 mph sat behind half a dozen other riders. For all the scenarios the actual effort you use will differ greatly and therefore directly influence the actual calories burnt.”

Strava does estimate power based on rider weight, bike and elevation, but again it’s working with limited data points and that means the picture it produces is pretty vague.

The same theory applies to running, too, though probably to a lesser degree as the speeds will be lower. “Strava can’t determine whether you ran in grass or tarmac, where a running speed of say 10 kilometres per hour would require different energetics on both surfaces, which would affect the calories used,” Howard explained.

So what should I do?

For those using calories burned for guiding weight loss, Howard wouldn’t focus too much on the calories used given the problems with Strava and the like.

“Instead, just try reducing carbohydrate intake on your low intensity training days and try fasted training: training in the morning before breakfast or if training in the evening don’t eat anything after lunch, as this will stimulate greater fat metabolism.”

Maybe it’s Dan and his conspiracy theories rubbing off on me, but I’m going to take the readings with a pinch of salt (rather than a lump of sugar) from now on.

I’m not sure Strava have complete faith in their numbers. Take a look at the cycling and running data the firm compiled for the UK in 2016 and it shows 16.9 million people uploaded their runs to the social network, covering 132 million kilometres. There were also 27.4 million rides and a host of other wonderful stats, but ‘calories lost’ are nowhere to be seen.

Coincidence? “I’m sure you can appreciate we have many data fields to work from, but will definitely put forward your suggestion of using calorie figures,” said their PR man.

Will they consider a new algorithm? Who knows, but as one user suggested: “Strava really needs to consider using a different formula for calculating calories. There are people who depend on accurate information as they are trying to lose weight.” People like me.

Don’t get me wrong though, I still love Strava and am not going to stop using it anytime soon – you can even come and join our Yellow Jersey Strava Club.

Do tell us if you’ve had similar issues, because it doesn’t seem like this has been picked up in the UK yet.

Ryan Georgiades

| 6 months ago

About this author:
Hi I’m Ryan Georgiades, co-founder of Yellow Jersey Cycle Insurance. When I first joined my local club, the Clapham Chasers, in 2009 I was 20 stone and heading for a heart attack. Cycling and triathlon truly change my life. Over the next six years I went on a journey which saw me lose six stone, get married to a club mate, have two children and become an Ironman. I’m currently training for nothing in particular and desperately trying not to get back to 20 stone.

I really hope you like what we are doing at Yellow Jersey, we are genuinely passionate about our sport and business.
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