I wouldn't worry about that. Even if you rode 4 hrs a day, you'd still be stimulating your bones more then some business or office person, who had to sit in a chair all day long. As they roll from desk to file cabinet, how much bone activity do they receive? Then they walk to elevator, then to car, commute home and walk to sofa. Then walk to supper table, shower and go to bed. I'd go with cycling any day and not worry.
Dickey Greer
West Monroe,La
USA