Ho@Home

Cogito, ergo I blog.

Archive for the ‘exercise’ Category

Burn, Damn You Calories, Burn

with 2 comments

Cateye Velo 8Ever wondered how bike computers, steppers, treadmills, etc. calculated the Calories Burned from just your speed and travel time?  Neither did I, until I discovered that my new bike computer said that I only burned around 290 calories per day riding to and from work – the equivalent of one thigh piece of KFC. Surely I was burning up more than that, right??

The textbook method of calculating calories burned looks something like this:

Calories burned = ((METs * 3.5 * weight in kg) / 200) * duration

There are a few things that stood out when I saw this.  Firstly, MET stands for Metabolic Equivalent of Task, which is essentially the amount of heat produced by the body when exercising, and can be fudged in part by using the average speed.  Fair enough.  However, the formula also requires my weight, which the computer doesn’t know.   What other assumptions must it be making?

I emailed Cateye to find out from the source.  To my surprise I got an answer, and within 24 hours (kudos to Cateye for actually responding!).  Here’s what they said:

Thank you for your inquiry.  As you mentioned, since the calorie counter of the Velo 8 model is not adjustable for age, weight nor fitness level, it is an estimate calculated from an “average” cyclists data, and is usually accurate for most users to within 10%.

“Average cyclist”? “Most users”? “Within 10%”? Really?

To test this, I googled and found this online calorie calculator, which conjures up the magic number by activity, weight and duration.  Punching in my figures gave me this:

caloriesburned

132% more than what the computer said.  I am obviously not what Cateye consider “most users” or “average cyclist” (which I find hard to believe).  After a bit of trial and error, I came to the conclusion that Cateye’s “average cyclist”  must be around 72kg and cycles at a “leisurely” pace (of around 3.7 METs, approximately half the METs of cyclist going at 12-14mph):

caloriesburned-leisure

So I was burning up more energy than I thought I was.  Hardly definitive proof, I know, but still.

The moral of the story is: don’t believe everything your trip computer tells you.  Or rather, if you google hard enough you can find facts to justify anything.  As for me, it’s a 2 piece feed for lunch tomorrow …

Written by Richard

12 March, 2009 at 9:58 pm

Posted in exercise