I did a bunch of research on homemade wind turbines the last few days. It's very much possible to run a miner off of previously stored energy in a battery through an inverter. If that energy just happens to be made from a person peddling a stationary bike it won't change the outcome. Just the energy source.
It's not meant to run it full time but as a secondary source.
Taking some big 4x2x1/2 neodymium n52 magnets and some 14 gauge enameled copper wire. Coil the wire, run magnets opposite polarity across the wire in a 3 phase configuration, you produce AC current.
Hook it up to a 3 phase rectifier then to a charge controller to a battery bank you get DC power stored in a battery.
Run the battery bank to an inverter to change back to AC current and you can use that to power any electronic. Just depends how long before you need the grid again.
Hook the inverter up to your breaker box correctly, you shed cash from your power bill. This might have to be done by an electrician if you do this.
If you think I'm saying, "yea I'm going to power a miner for days from this." That is not at all what I'm saying
It may take a week to build up enough power for 15 hours of mining. But that's still 15 hours off your power bill. Also some exercise.
Now if you hook blades up to the stator(diy alternator) you can turn it into a wind turbine in the off time and possibly get more.