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Old 12-03-2015, 04:21 PM   #2
Patrick A Horsman
Affiliate Patrick A Horsman is offline
Join Date: Jan 2014
Location: Halifax  Nova Scotia - NS
Posts: 34
Re: Redefining the relationship between Power and Intensity

Originally Posted by Dane Thomas View Post
The terms "force", "work", "distance", "time", "power", "area", and "intensity" all have well-defined meanings within the field of physics, and the relationships between these terms are precisely understood. Power = Work / Time, and Intensity = Power / Area (where the area is an imagined surface that is perpendicular to the direction of propagation of the energy)

When writing for a more general audience there is a natural temptation to descend from these precise usages to more colloquial definitions. I do not, however, feel that this makes it accurate to claim that in the field of human performance "...power is the definition of intensity...", or that "...intensity is defined as power.". I can memorize those phrases to get a better grade on a certification test, but that does not make them factually correct. Likewise, the fact that the phrases came directly from Coach Glassman in an article published in 2002 and have been repeated by countless other since then also does not make them any more scientifically accurate.

It seems to me that a program that is empirically driven, clinically tested, and community-developed, with an open-source charter that makes co-developers out of participating coaches, athletes, and trainers through a spontaneous and collaborative online community should welcome a discussion on this topic. Doing so could improve the general level of understanding and consensus, and potentially enhance something that is already very good. Think of it as a way of chasing intellectual virtuosity.

Please be assured that I understand and agree with the spirit of the point being made by the phrases. I just think that making the point while respecting the terms in question would make the argument more sound.

I think that it would be more accurate (yet still understandable and meaningful) to say that power is directly correlated with intensity, which in turn has been linked to nearly every positive aspect of fitness.

Anybody else out there agree? Is it more laudable to preserve dogma for dogma's sake, or to improve upon it when the opportunity arises?
I suspected that: "The word "intensity" [as used here] is not synonymous with "strength", "amplitude", "magnitude", or "level", as it sometimes is in colloquial speech" (directly from wikipedia on intensity).

However, if it was intended to be used in the true physics since (which I doubt) I still believe it is relatively accurate.

Given that Power = work / time and Intensity = Power/Area then it logically follows from the same article that if we are discussing a moving object rather than a wave:

"Intensity [of a moving object] can be found by taking the energy density (energy per unit volume) at a point in space and multiplying it by the velocity at which the energy is moving. The resulting vector has the units of power divided by area."

Energy per unit volume may differ from person to person, but within the individual with a given implement in a given workout the unit volume would be a constant no matter how fast the individual was moving. Thinking about it differently, the dimensions of the imagined perpendicular surface for each movement would not change.

if Area is therefore a constant when comparing within the individual (=1) then Intensity (within an given individual) = Power /1.

Given that we define intensity in CrossFit as only being relative to the individual I think the statement that Intensity = Power is actually accurate.

Also I think you can tell I had some time to kill at work today.

Last edited by Patrick A Horsman : 12-03-2015 at 04:35 PM.
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