Since I don't have Pa Kua classes anymore and there's still almost a week to go home, I decided to find places to go running.
Usually, people will indicate the Le Cascine park, wich is a little west from the central station Santa Maria Novella, where you can also find a street market if you stay in the road along the Arno river, the Viale Abramo Lincoln. Another place is at Nave a Rovezzano, wich is in the other side of the river and of the town center (a little after Piazza Beccaria if you're on the northe side of the river or from Piazzale Michelangelo if you're south).
I also found a program that indicates routes trough the city's streets, from the simplest and easiest ones, to longer and more dificult ones, like going up to the Piazzale Michelangelo and take the chance to enjoy the view.
http://www.turismo.intoscana.it/blog/wp-content/uploads/2009/11/walking-pieghevole-48x48_page_2.jpg<- the descritions of the routes (in italian)
http://www.turismo.intoscana.it/blog/wp-content/uploads/2009/11/walking-pieghevole-48x48_page_1.jpg<- and the routes indications.