# Making the Most Out of a Jog

## Introduction

 Fig. 1: Will running help you charge your phone? (Source: Wikimedia Commons)

## Background

Have you ever heard about Rafael Nadal, Peyton Manning, and LeBron James? What do they have in common? They are all athletes. Consider how much energy they have produced in order to play their sports throughout their careers. And now multiply the average of those three numbers (in calories) by the number of all athletes in the world. Next, figure out the average amount of energy one person in your family uses to play sports recreationally during their lifetime and multiply that by the remaining number of people in the world. Finally, convert joules into kilowatt-hours. It is a pretty big number, right? Definitely not big enough to solve the world's energy problem for centuries but significant enough to be explored in more detail. Let us take a quick look at the numbers. According to MIT PhD candidate at the Department of Mechanical Engineering, Killean Stark, an athlete who commits to 1 hour workout on the treadmill every single day will produce 255 kilowatt hours per annum (for comparison, an average single-family U.S. home consumes around 600 kilowatt hours monthly). That means that we would need roughly 30 athletes (600 × 12/255) to satisfy the yearly demand for electricity of a single-family U.S. house. It sounds promising, doesn't it?

## Idea

So where does the energy produced by athletes go? What if we could utilize this energy, store it and actually use it to generate electricity?

Transformation of the kinematic energy produced by people into electrical energy has been explored for quite a while already. [5] The world's first sustainable dance club was opened in Rotterdam in 2008. Its dance floor is lit up only thanks to the kinematic energy produced by people's feet pounding on the dance floor. [6] This is possible thanks to the piezoelectricity effect and even though only a small part of the energy produced by dancers is currently being transformed into electricity it has a bigger social impact than one might think.

[3] Another example comes from the first self-powering weight room which was opened in Congresbury, United Kingdom, in 2013. Bikes, cross trainers and "vario" machines are able to consume energy produced by their users and if there is any surplus of energy they can also store energy inside a holding cell or a dynamo which would then feed this energy into the building's electricity supply.

The equipment required to implement these innovations is obviously expensive (around \$250,000 for the dance floor and around \$900,000 for gym machines). However, I have deliberately disregarded the costs of such technology because I believe that technology advances faster than we predict and sooner or later the costs of these complicated mechanisms will decrease.

To better supervise their practices and progress many athletes wear Heart Rate Monitors. They are just watches connected to a sensor that you place below your chest. You can observe how your heart rate changes during practice but what is more interesting this little device also tells you how many calories you have burnt. And here comes my idea. Let us fast forward and look 20-30 years into the future. I see myself placing a small box in a shoe and going for an hour-long jog (to help your imagination, please look at Fig. 1). There is a small dynamo in the box which transforms all kinematic energy produced by me during the workout into electrical energy and stores it for some specific time. I also put a watch on my wrist, wirelessly connected to the dynamo, which continuously informs me how much energy I am saving. When I get back home I plug my little box from the shoe into the battery that absorbs electrical energy that I produced during the workout. This 1-hour workout enabled me to charge my phone. The watch and the technology installed in the house is affordable for everyone. Sounds too good to be true? Maybe, but why not dream? Military is already using backpack technology and knee braces to harvest energy from walking, so why can't such solutions become available to a wider public in some time, following the example of the internet which had been used by military first before regular people could take advantage of it?

## Conclusion

It is crucial to notice that the watch (along with the human's usual workouts) is not completely replacing other sources of electricity. It should only supplement natural forces' energy (wind, sun and water). What I see as a significant step forward in our efforts to cope with the energy issue is a big social impact it might have on people. We would all feel more responsible for the natural environment because we would actually feel that by doing certain things we would be protecting our habitat.

© Maciej Romanowicz. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

## References

[1] H. Anderson "Levi's Stadium Efficiency," Physics 240, Stanford University, 10 Dec 14.

[2] K. Belson, "For Eagles, a Winning Mix of Wind, Biodiesel and Solar," New York Times, 17 Nov 10.

[3] L. Edmonds, "World's First Self-Powering Gym," Daily Mail, 24 Sep 13.

[4] F. Hernandez, "Harvesting Energy from Soccer Balls," Physics 240, Stanford University, 28 Nov 10.

[5] E. Rosenthal, "Partying Helps Power the Dutch Nightclub," New York Times, 23 Oct 08.

[6] S. Winger, "Piezoelectricity from Dancing," Physics 240, Stanford University, 24 Oct 10.