Wrist-watch type human power meters....

[houlahound]

I would like to get a handle on human Wattage under various conditions.

it would be great to compare theory calculations of say running up stairs with how much ACTUAL wattage it takes...just for physics fun.

the only common bench top measurement device I can think of is those wrist-watch type exercise meters.

my guess is they read your pulse and get a heart rate and maybe calculate the mass of blood being pushed around your body and come up with Watts, just a guess?

anyone know how these devices actually calculate power?

 

[CWatters]

As I understand it they don't/can't measure power output directly. They can only measure what they believe to be proxy parameters and apply a proprietary algorithm. I suspect the algorithm they use in a device aimed at runners won't give reliable results for cycling or swimming. The experiment you propose may end up testing how good their algorithm is.

 

[CWatters]

One device I found on the the web is mounted on a belt and measures how fast you are running (strides per min) and impact shock. It didn't say how they turn that into power.

 

[Fervent Freyja]

Some of those watches go by the number of calories burned per hour by combing heart rate or activity settings. This website converts it to watts for you: http://www.convertworld.com/en/power/calories-per-hour.html

 

[sophiecentaur]

how much ACTUAL wattage it takes

Very difficult. The only relevant value is the Work Done On your body by raising it up those stairs. It is possible to meter the total rate of respiration of food over a period. Gas analysis of your lung output can tell you how much CO₂ you produce per minute, which will tell you how much glucose your muscles are metabolising. In between is vast unknown territory. Any gizmo that you strap on can only give a rough estimate of what power is going into the muscles that are doing the work. I guess it should be possible to calibrate such a machine against the results of total in against total delivered power. I have no experience of such instruments. Do they give consistent results? That would be one way to see how much you can rely on what they tell you. But many people get a lot of fun from using them.

 

[houlahound]

I guess as long as they are consistent they can be used to assist in a rational physical fitness program for the individual user... too hell if the numbers are kind of fake in the physics sense.

Obesity is becoming a major public health issue in the west so good for the gizmo thingy.

 

[CWatters]

it would be great to compare theory calculations of say running up stairs with how much ACTUAL wattage it takes

That amounts to calculating the efficiency of a human while climbing stairs. Google can find...

http://www.birmingham.ac.uk/news/latest/2011/03/07Mar-Stair-climbing-reduces-energy-bills.aspx

Humans work at only 20% efficiency when climbing stairs and each calorie expended when climbing produces four calories of heat.

 

[sophiecentaur]

"Humans work at only 20% efficiency when climbing stairs and each calorie expended when climbing produces four calories of heat." Not amazingly good but a lot better than thermodynamic efficiency of a heat engine working between those sorts of temperatures. Quantum rules in our cells.
Edit: I just finished reading 'Life on the edge', by Jim Al-Khalili, who's a Theoretical Physicist, author and broadcaster. The book discusses the idea that the biochemistry of life works at the quantum level ("edge") because the processes involved just wouldn't work on a thermodynamic basis. A good, convincing read and it was on offer with Kindle, too! I recommend it.