Distance v time v energy

Question for those in the know…

I’ve done the same route twice this week, once in snow and ice so very slow and once after it had thawed.

Difference of 20 minutes as I had to ease along / down some of the bits when it was icey. (Nothing like sliding down a piece of singletrack to get your heart going!!!)

The bit which puzzles me is from a calories side of things I did about the same amount.

When I was at school I always remember a physics teacher telling me you exert the same amount of energy moving a 1kg weight up 1m whether you do it in 1 sec or 10sec.

Is this that principle in effect or is it just a fluke that the energy expended is the same?

I should add that my Average HR was 133 for Slow ride and 147 for fast ride

Calories same
Distance same
time – 20mins difference

Currently happen to be doing A-Level physics, so I’ll have a go.

Your physics teacher is right – change in energy for moving something up or down is mass x 9.81 x height, so nothing about time.

However, that is too overly simplified for the human body. Your muscles are going to use more energy holding the bag of sugar for an hour whilst raising it 1m than they would in raising it in 10seconds.

I’d say you’d use more calories because you would be fighting to controll the bike more, and tensing / untensing muscles more.

Overall, not really related to time, just how much work your bodies muscles are doing.

I would have thought you would transfer less when its icy perhaps (not taking into account MM’s theory)

If you do it as fast as you can I would image you would be constantly pedalling in a hard gear, whereas if you did it when it was icy you probably wouldnt be pedalling all the time, alot of the ride would be freewheeling so you wouldnt transfer as much energy?

Work done (j) = Distance x force

So technically time doesn’t come into it, but

Air resistance is proportional to velocity squared so the faster you go the more air resistance so you will need more energy to go faster.

Calories = energy. You were working at different power levels on the two days, power = rate of expenditure of energy, so if your power drops your time increases but the energy is still the same. As said above, it will not be exactly the same due to muscle efficiency effects but within two reasonably close average power outputs (i.e. not comparing 10 mins to 10 seconds) the net result is going to be very similar.

How did you measure the calories used?

Ah yes interesting, but then there’s the energy spent by the body keeping warm when it’s colder…

😕

TJ – could start a interesting thread if I say it was a HRM.

I am wondering if on the uphills I used more energy due to wheels slipping and I perhaps was slightly slower due to having to concentrate on grip more and downhill I was very much slower as it was seriously sliddy and I also didn’t have as much momentum because I was travelling slower to get up the uphill bits after the fast bits – meaning that overall – I perhaps used less energy on the uphill and more on the downhill on the slow route rather than the fast route. So the energy balances out.

However, I still wonder if there is something in it being to do with the amount of mass moved a distance / height.

HRM calorie calculations are usually pretty inaccurate, the algorithm Polar use is supposed to be one of the more accurate ones.

Yeah – its a Polar

I’ve just had a quick look back through my Polar training software, and for the same 18 mile route on the Quantocks I’ve taken 1hr 28mins, ave speed 12.3mph, ave HR 151bpm, 1183kcal and 1hr 51mins, ave speed 9.5mph, ave HR 139bpm, 1312kcal.
You’d think the faster ride would burn more calories, it certainly felt like it.

Now thats bizarre!

If you are measuring calories burnt of a HRM it will have little relevance. I would be very loathe to draw any conclusions from such an estimation of calories burnt.

Try walking for 20 minutes.

Now try running for 10 (at twice walking pace).

What’s the biggest difference?

Sweat.

When you delivery more power you generate more heat. That’s wasted energy as far as travel goes.

So no, you don’t burn the same calories going different speeds.

I’m sure I read somewhere that HRM calorie calculations have an accuracy of +-20% so I can’t say I’ve ever taken that much notice of mine.