We are preparing for our annual visit however this year we are staying on the French Side. Does anyone have recommendations for a fitness centre?

Where will you stay? Some of the hotels have workout rooms example Grand Case Beach Club.

If you walk the beach and walk the hills in the little subdivision in Orient Village it will give you a workout.

We are staying in a private condo in Mt Vernon but will have a car. We normally stay on the Dutch side and use the gym at Port de Plaisance.
I'll check to see if the GCBC allows outside drops ins. I was looking to see if there was a fitness centre that the locals use.
If all else fails a run on the beach will create more room for French food and BBQ ribs

Yes, a very nice fitness center upstairs just past the entrance to Hope Estate. Near the old SIMPLY Market.

Gymfit in Hope Estate. Enter Hope Estate at the roundabout and it is on the left, upstairs.