Kay is right, also consider a run outside with loads to keep em active
pipes, pots, old shoes etc and also plenty of handling.
I often sit in the run ferret court with em for about an hour
chills me out after work and gives em something different to run over
and investigate.
helps with bonding to the animal as well.
I found over the years that putting a collar on with a cat lead and
"take em for a walk" helps fitness also has the side affect of getting them
used to a collar for the season
cheers
anton