I had a couple of rabbits, whose one of them used to gnaw at the cables, but it can't be helped, it's in the nature of a lion-headed dwarf rabbit

I had to confide them to my father because I never had the time to fully take care of myself.
A treadmill can be great, or a home bicycle, whatever. I believe walking for a decent time quite regularly and riding a bicycle on the street is simple and efficient, then it's up to everyone to find its own way of improving endurance.