The idea in some form probably has merit but
You'd need strict supervision to make sure no one was so amped up by the game that he hurt himself on the machines. And the captain would need to coordinate when someone moved from one machine to another. For example, if you were being attacked and needed stronger shields, you might move your most buff teammate to the machine controlling shield power until the threat was over. If speed was most important, you'd put your speedsters on the treadmill. Or maybe at some point everyone would have to "lift" at the same time to get over an obstacle. The variations are limitless.
sounds a lot like it would actually get in the way of an effective workout. It's not a good idea to just arbitrarily jump from one kid of exercise to another, and if the game was any sort of actual game (as opposed to just a leader board)the emergent gameplay would mean just that