Hi Kim!
Port Orleans Riverside is a lovely Resort! It is quite large, and there is lots to explore, so even though there is no fitness center on site for guests, there are several recreational amenities available that you can utilize to get your "work out"!
You can walk, run, or ride a bicycle along the banks of the Sassagoula River on the 0.7 mile paved jogging trail. I have done this before (walking) and it is so peaceful and beautiful! Bikes and surreys are available for rental at the Resort.
Also, there are SIX swimming pools throughout the entire Resort! So, you will have a great choice whenever you want to log some aquatic miles!
There are
fitness centers available at several of the other Disney Resorts which you, as a Disney Resort Guest, will be allowed to use for a fee. Please check with Guest Services at your resort to determine the best choice for you.
Have a wonderful time at Walt Disney World!