For reference later on, the Swiss “Designwerk” company has built a prototype of a fitness bike that stores the energy generating by riding it. Users can store the electricity in a battery or plug in some appliance directly. In that case they will feel the load on the bike, making this an interesting educational tool. It also might make sense to store the energy if one is generating it anyway for fitness purposes.
Found over this story at Cleanthinking.de.
As explained earlier in this post, human muscle power does not amount to much. It would take a person all day to generate even one kWh with such a device, which shows how ridiculously low prices for energy are in our age compared to a couple of hundred years ago.