There is a medium to large (by ship standards) fitness center on the Sun. There are several quality treadmills, some bikes and a step machine that are in use heavily for the first couple of days. They also have a good assortment of Cybex weight machines (however the biceps curl was broken when we were on her in February), Some free weights (dumbells only) and an adjoining large aerobics room with classes all day long.
There is also an acceptable jogging track on the ship. Something I like to do in port is to have a taxi drop me a few miles outside of where the ship docks and then make my way back. I usually walk but it would also work to jog if you folks want to get some on-land exercise. The cab drivers look at you like you are nuts sometimes, but it is a great way to get some exercise and also get the true flavor of the port.
Have a great cruise!