If all the world's gym machines were adapted to be used for electricity production, let's take the calculator to see what would happen. There is an effort, from a US company called ReRev, assuring that for each 30 minute workout you could get 50 watts-hour of electric energy.
A laptop should consume less than that, and there are a lot of electronic devices that will run an entire hour thanks to this energy.
Probably, this is not the only waste that we are seeing every day, for sure we have other methods to get energy, from different sources ... the problem is to identify where.
From our part, we are pretty sure that gravity is one of the best energies to use because it's always there. We encourage you to think about a method to create energy from gravity, for sure better if you achieve a constant cycle for solving the worlds' energy problem forever!