Domestic exercise and energy

You know, yesterday it occured to me that there is a craziness in modern life I had never seen before. In the red corner we have loads of people buying gadgets to exercise with many of which use power to maintain them. In the blue corner we have a need for energy production which doesn't use fossil fuels and is renewable. We also have pretty good technologies for turning motion into electrical power. So why is it that no-one has put together, first of all, self- powering exercise machines [perhaps they have?]. And then going on from there are any exercise gyms making extra cash by either using their equipment to generate power to offset their own usage or even to sell the extra to the grid? And then going on from there, it is just becoming possible for us to do similar things domestically; so who will come along and offer us a domestic electricity generator that uses human muscle power that both gives you exercise and helps to power your home, thus giving rebates on your fuel bills? If we have to do 10,000 steps per day why not give the incentive to cut your fuel bills? Link up between Health agencies and power concerns?