We put out some hand weights, a jump rope, a stretching thing, some exercise circles, and a couple of beanbags (for balancing). I made a tape line for balancing, too. We spread a towel "mat" on the floor and added a gym sign.
The kids that came in first immediately began to lift the hand weights. They showed their muscles. They lifted weights up and down and did a few curls, too.
When I pointed out the tape line, they walked along with it, with weights and without them.
They investigated the other items, too. Kids would move into and out of this area all morning.
Then a boy used the tape line and made his own obstacle course. As he and his friend walked through the course, they kept modifying it and experimenting with it.
This activity was an unqualified success. I thought of a couple of other items that could be added next time we try this. They loved it.
Kids continue to surprise me and teach me. Mostly they teach me not to assume I know anything about what will happen when kids have a chance to explore...anything.