Would you make him go?

I am seriously considering joining a gym, so I was able to wrangle a free 30 day pass. All I really want to use the gym for is classes for cardio and strength. I brought my boys with me when I picked up the pass and they spent a couple of minutes in the kids room. When we left my oldest son (10) flat out refused to go in there again. He says he will not go in no matter what because it is for little kids and there is nothing for him to do. I have taken away privileges, threatened grounding, and even told him he could bring the laptop and play with that, but he is still refusing. I really want to take these classes and get in to shape but I’m not sure what to do. How do you decide which (parenting) hills are going to die on?