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Workout cycle from PlugOut, a supplier of exercise equipment that turns your sweat into electricity.

The last time I was at the gym walking on the treadmill, I looked around and saw dozens of people sweating away, running, climbing stairs and pedaling bikes, all under the bright lights and cooling air conditioner breeze. And I thought, wouldn’t it be great to turn all this sweat energy into electricity that could power the gym and maybe return something to the grid?

We could turn gyms into power plants. You pay the gym and they sell your sweat-generated electricity to the power grid. I wasn’t  the first person to have this brilliant idea. There are now dozens of gyms around the US that have implemented this idea and a number of vendors who supply modifications to existing gym equipment that convert your sweat into electricity.

But, the value is not in the electricity generated, it’s in the idea behind it. Just put in the numbers.

You can buy from the Bicycle Sports Shop, among others, a sensor that will measure the power you expend in riding a bike. They offer a handy table with a few numbers for the typical power that a human can generate.

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Two numbers are of interest. The peak power is the average power over a 1 minute interval of sprinting. The functional threshold is the average power that can be sustained over a 1 hour period. These are power per kilogram of body weight. You take your weight in pounds and divide by 2.2 to get your weight in kilograms.

Suppose you weight 220 pounds. This is 100 kg. A trained athlete can generate about 6 watts/kg x 100 ~ 600 watts over an hour. One of us mere mortals could generate about 200 watts, or about 0.2 kilowatts of power. For reference, this is about 1/4 horsepower.

Energy costs around the US vary but a reasonable starting place is about $0.1 per kW-hour, or 1 cent per 100 watt-hours of energy.

This means that a person working out might be able to generate about 200 watt-hours of energy in an hour of hard and steady workout at the value of 2 cents. If you have a room of 50 people all sweating for an hour, the value generated would be about $1.

This revenue stream is just not a viable business plan. However, if you had a choice between going to two different clubs, one that you just sweated at, and one at which you sweated, but knew that each drop of precious sweat generated some, even tiny amount of electricity that was put to good use, which club would you want to go to?

When competition between gyms becomes more fierce, small differentiators are large deciding factors. I think the clubs that offer to turn your sweat into generated electricity will become more popular, even though the amount of electricity generated is trivial. It would be about enough to power the LCD screen of the TV you watch.

The ROI for a gym is not in the revenue generated by the electricity generated, but in the additional number of user who would be attracted to sign up if they knew their energy was being put to good use.

In addition, an exercise machine set up to generate electrical power is also instrumented to display the power generated. This is yet another metric that you can use for feedback to help you feel better about your workout.

And after all, isn’t a large part of working out about feeling better about yourself?

Electrical power generating gyms will not become the power plants of the Matrix anytime soon, but they will make you feel a little better.