Treadmill, bicycle, or exercise wheel electric generator

Anyone have one or plan on having one?

My husband asked for a way to run indoors and have that produce electricity. There's one treadmill not fully on the market that can do this (the Verde). In a tiny house video I have seen an exercise wheel that was more or less a hamster wheel for adults. I have also seen bicycle energy generators.

I don't think we have space for a giant treadmill or hanster wheel.  So I either have to invent something smaller that fills the running function (unless you already did) or go with the bike option. Any ideas?

It seems to waste a lot of energy just for producing heat. It's better to transform the bike to do a specific job. For example: attach it to a lightbulb - I've seen it in one theatre as part of stage design, the cycling actor had quite a workout during entire show! Or make it into a flour mill (my friends have it; they only buy grain and produce their own flour from it). This way you will use the energy better. If you just want to produce electricity and then plug something in to use that electricity for lighting the bulb or grinding the flour, you will waste a lot more of it.
I have also seen treadmills with usb which can charge a mobile phone, on display in one gallery, but it takes a really really long time to charge it.

There are also manual generators but their efficiency also seems rather low...?

A quick search finds several companies producing human powered generators:
https://youtu.be/OSXldBRtVxM
https://windstreampower.com/
https://www.amazon.com/Pedal-Power-Bicycle-Generator-Emergency/dp/B003GJL6GO
I do not work for and I am not affiliated with any of these companies. They are just examples I picked randomly.