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Fitness Theory and Practice. CrossFit's rationale & foundations. Who is fit? What is fitness?

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Old 05-22-2007, 07:50 AM   #1
Jason Arsenault
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I had once read about a formula to calculate power from FRAN. Where can I find that again? And would the formula work for all?
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Old 05-22-2007, 08:11 AM   #2
Jon Gilson
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Jason,

Power = work/time = (Force * distance)/time

You would need to know how much weight you were lifting, how far you moved it, how much you weigh, how tall you are, and how many times you moved both yourself and the weight.

Or you could just use the Performance Menu Power output calculator and save yourself a lot of trouble:

http://www.performancemenu.com/resou...owerOutput.php

WFS link.

Best,

Jon
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Old 05-22-2007, 08:33 AM   #3
Jason Arsenault
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Wow, thanks, thats pretty handy. Beats doing math manually!
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Old 05-22-2007, 09:54 AM   #4
Roger Harrell
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I'm curious how the force has been calculated in these cases. Has actual acceleration been considered or just 1G. Eg someone does a 95lb squat. Is force being calculated at just overcoming gravity, or is the acceleration upward being considered. A thruster done quickly actually involves more work because the force throughout the movement is greater than one done slowly (or the force at the beginning is substantially greater to create the higher velocity which is then maintained). In any case, work is greater if the rep is faster. So power would be dramatically higher because it's more work in less time.
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Old 05-22-2007, 12:16 PM   #5
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roger -

the calculator is definitely not precise (but no less precise than doing the math manually).

the force is being calculated indirectly by calculating the power. so if i at 5'11" and 205lbs do 1 thruster at 95 lb in 5 sec, that's 161 watts. if that thruster is done in 1 sec, it's 805 watts. so if you're doing multiple reps and accounting for the time of completion, you're assuming that more reps in less time = faster reps.

now of course you could fudge that up by resting during the total work while performing the reps at the same speed, but again, this is an estimate of work/power, not an exact figure. i would say a bigger concern is that we're not accounting for the work done during the eccentric portion of the movement--i think that''s much more significant than variations in acceleration. really what it boils down to is that being precise with this stuff requires way more data than can be collected and measured outside of the lab. the PM calculator is just a quick and simple way to compare workouts for the same person (as well as just one more thing to waste time with at work).
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Old 05-22-2007, 12:42 PM   #6
Roger Harrell
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I expected that to be the case. Trying to be more accurate would require some pretty complex time based calcs and would still involve some pretty substantial assumptions (all reps performed at the same speed, travel rate constant throughout ROM, etc). I'm not sure that it would be any better. The essentric phase would be an interesting calc. It could range from being almost the same as the concentric (controlled descent) to virtually no work performed during the descent with a dramatic work spike at the bottom (catching). It would be interesting to see how the numbers differed for the same exercise/person/weight.
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Old 05-22-2007, 12:54 PM   #7
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yes... when eva t and i first embarked on the project, it seemed remarkably simple. we very quickly realized there were just far too many factors to consider and just decided to accept a certain degree of inaccuracy.
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