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Old 07-25-06, 04:45 AM   #1
corny
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Calc'd my Power Output: What does it mean?

First off please forgive my incompetance, I am new at this!

I was on a stationary bike in the gym yesterday, a SportArt 5200U as it happens

I clocked 25.00 mins covering 12.2 Km at load 6, 95+ RPM (not that that means anything!) burning 520 calories according to the onscreen calculator.

Converting this to Power means a power output of 1450W for 25 mins - is this any good? More over, is it likely to be at all accurate?
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Old 07-25-06, 05:11 AM   #2
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Damn, you're better than Lance!

Read this guide and you'll see why I said that:

http://www.bicyclepowermeters.com/Er...ng_English.pdf
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Old 07-25-06, 06:02 AM   #3
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Interesting (quick!) read, thanks for the link. I shall try to make my way through it!

In short though, it seems that the bike must calculate the calories incorrectly, are there any values (like the table on P14) for power output over 20-30 mins available just for a few ideas however?

Not sure it makes much sense at the mo as i weigh 67 Kg, so achieve 21.6 W/Kg for 25 mins!?!
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Old 07-25-06, 07:57 AM   #4
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Quote:
Originally Posted by corny
Converting this to Power means a power output of 1450W for 25 mins - is this any good? More over, is it likely to be at all accurate?


Yeah, that's pretty good considering Zabel can "only" push 1400-1500 during a final sprint. He certainly can't hold it for 25 minutes.

No, it's not accurate.
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Old 07-25-06, 08:08 AM   #5
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Yes, it's probably accurate. The reason is that your body is only about 20% efficient at cycling. That is, to put out 200 W of useful power (useful = used to move yourself and your bike forward), your body has to work at a power level five times that, or 1000 W in this case. Your 1450 W, divided by five, comes to a decent 290 W. The power not going into your pedals produces heat in your body.

However, since you used a piece of exercise equipment, it's designed to tell you how much energy you used during your workout, and that has to be done using your total power output. It probably knows the power required for every RPM/load combination and multiplies that number by five.
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Old 07-26-06, 05:52 AM   #6
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The OP calculated the average power himself, based on the energy expenditure figure the exercise bike reported. That's why the conversion is quite correct. And that's also why the numbers are correct.

290 W for 25 minutes is perfectly normal.
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Old 07-26-06, 06:09 AM   #7
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Quote:
Originally Posted by CdCf
The OP calculated the average power himself, based on the energy expenditure figure the exercise bike reported. That's why the conversion is quite correct. And that's also why the numbers are correct.

290 W for 25 minutes is perfectly normal.
@CdCf

Thanks for your comments - what you have said makes sense!

Shame its only 'normal' though lol!

Cheers!

James
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Old 07-26-06, 10:17 AM   #8
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While it's in the right range, who knows how accurate the thing really is? If it's off by, say, 25%, it could be 360 W. And that's really good! 290 isn't bad either. Far more than I'm capable of, but then again, I'm crap...
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Old 07-26-06, 04:51 PM   #9
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Quote:
Originally Posted by corny
First off please forgive my incompetance, I am new at this!

I was on a stationary bike in the gym yesterday, a SportArt 5200U as it happens

I clocked 25.00 mins covering 12.2 Km at load 6, 95+ RPM (not that that means anything!) burning 520 calories according to the onscreen calculator.

Converting this to Power means a power output of 1450W for 25 mins - is this any good? More over, is it likely to be at all accurate?
Exercise power and calorie measurements are wildly inaccurate. There's no reason that such a device couldn't be very accurate, but they aren't. I presume either 1) it's more expensive to be accurate or 2) people like the inflated values, or 3) a little of both.

Burning 500 calories in an hour is a pretty good level of effort, for comparison.
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Old 07-27-06, 01:42 AM   #10
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Thanks for your comments guys.

I contacted cyclingnews and they said:

The main issue is simply going to be whether the indoor cycle is accurate
or not. Most gym cycles I've seen have been terribly inaccurate (above or
below the actual power output). There's also the question of whether the
data is reliable or not (is 290 W on the unit, 290 W every time you ride
it, or a different amount?).

If we speculate that the 290 W is correct (although it isn't likely to be)
that effort for a 67 kg rider is good effort -- it's likely around what 2nd
and 3rd category racers can do over a 10 mile/16 km TT effort.


Following that, I contacted SportsArt regarding the accuracy of the calorie counter - and they have said they will get back to me.

Cheers,

James
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Old 08-01-06, 03:56 AM   #11
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A bit of an update...

I used the power information from the pdf document, and calculated my 5 minute power output.

I burnt 136 kcal in 5 mins, which is 1896.75 Watts of power.

Assuming the same efficiency of 20%, I put out 5.66 W/Kg for 5 mins.

If this is at all accurate (highly unlikely!!!) it puts me just inside Cat 1!
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File Type: bmp Power.bmp (43.0 KB, 3 views)
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Old 08-01-06, 07:11 AM   #12
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Quote:
Originally Posted by corny
A bit of an update...

I used the power information from the pdf document, and calculated my 5 minute power output.

I burnt 136 kcal in 5 mins, which is 1896.75 Watts of power.

Assuming the same efficiency of 20%, I put out 5.66 W/Kg for 5 mins.

If this is at all accurate (highly unlikely!!!) it puts me just inside Cat 1!

Well, the only way to put this to rest, is to get a "real" bike and ride with some good riders.

Let us know how it turns out.
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Old 08-01-06, 07:21 AM   #13
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Indeed - I have a new bmx to put a powertap on, its going to rock!!!


It has been interesting nevertheless to have a look, thanks to all that contributed!
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