# The Naked Scientists Forum

### Author Topic: How long do I have to work out for to work off a Mars bar?  (Read 4815 times)

#### thedoc

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##### How long do I have to work out for to work off a Mars bar?
« on: 28/01/2014 19:30:01 »
Exercise physiologist Dan Gordon explains how he pushes athletes to their limits and answers the audience's questions...
Read a transcript of the interview by clicking here
« Last Edit: 28/01/2014 19:30:01 by _system »

#### David Cooper

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #1 on: 29/01/2014 18:59:27 »
That's a good read, in places. I really appreciate the transcripts - they save a lot of time. How do you make them? I'm guessing that speech recognition is involved, but can you do that directly from the audio yet or do you have to get someone to listen to it in a quiet room and say it all again carefully? However you're doing it though, thanks.

It feels as if a lot of energy is still being burnt for a long time after the exercise ends, so it must be very hard to measure the actual amount of exercise needed to burn off a Mars bar. When Mark Beaumont cycled round the world he tried to eat six thousand calories a day to balance out the 100 miles or so of what was usually fairly gentle exercise - he wasn't going at race pace, but more like the speed of a Cyclists' Touring Club run. That's perhaps 4000 calories more than normal per day, and about 400 per hour. With high intensity exercise, I would guess that you could burn 400 calories in under ten minutes and might burn a good bit more throughout the rest of the hour.

#### alancalverd

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #2 on: 30/01/2014 12:03:01 »
Standard Mars bar is 260 kcal = 1.1 megajoule

Maximum continuous useful output for most people = 40 watts

So to work off one Mars bar you need to exercise hard for 27,300 seconds = 7 hours 35 minutes - a working day.

A coalminer, farm labourer, arctic explorer or professional athlete might just about do it, but no ordinary mortal could eat a Mars a day without putting on a load of weight.

#### David Cooper

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #3 on: 30/01/2014 19:30:35 »
Data from racing cyclists suggests otherwise. In the Tour de France they can average 250 watts or more on a stage, so the many ordinary fit people could do half that. That's just the power transmitted through the pedals though - far more energy than that is lost as heat.

#### chris

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #4 on: 31/01/2014 18:41:30 »
That's a good read, in places. I really appreciate the transcripts - they save a lot of time. How do you make them?

We have a team member who listens to the programme and produces a computer type-written version, which we check and publish. Laborious, but worth the effort, in my view...

#### David Cooper

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #5 on: 31/01/2014 18:57:18 »
Well, please pass on my thanks and appreciation.

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##### Re: How long do I have to work out for to work off a Mars bar?
« Reply #5 on: 31/01/2014 18:57:18 »