Touring Tuscany by bike has become very popular. There are many companies that organize bike tours, providing the bikes, meals and accommodation along the way. A minimum of good physical condition is required as many parts of Tuscany are hilly.
You can also bring your own bike but check with your airline for charges; you'll likely have to disassembled it and pack it well for the journey.
Once you are in Tuscany, many trains have a carriage set aside for bicycles that makes it easy to ride around different areas in Tuscany without the need to completely get from area to the next on bike. Check on timetables for a bicycle sign but note that Eurostars do not have this service. In any case, you'll have to pay a supplement for the bike of around € 3,50 that lasts 24 hours from the time you stamp your ticket so if you ride another train with your bike within that time frame you only pay once for the bike.