A new exercise

I have various pieces of exercise equipment in the garage -- free weights, Total Gym, medicine ball, punching bag. Nothing I have found, however, is any better at keeping me in shape than using a 50 pound weight named Big Sister and a smaller one named Little Sister.
They are the perfect size right now to give me the right amount of resistance.
Push ups with Little Sister on my back are challenging, but give it that extra burn. Big sister is the perfect size to walk on my back and also to stretch out my legs.
They have a lot of fun doing it too. I'm just a big jungle gym to them.
After a while that gets a little boring, just doing pushups and such. So the other day, after cleaning the garage, I realized the Total Gym has a bunch of pulleys and ropes.
I hooked up the pulleys and ropes to a hook in the rafters. Then I found a harness for Big Sister and we have a new exercise machine. Only this machine allows the sisters to fly like Peter Pan from the ceiling.
I know, it sounds dangerous, but there's nothing around for them to run into and the ropes and everything are in sound condition. I don't think I'd do it once the are past 70 or so pounds, but for now ...
There is one problem. I'm not in as good a shape as I should be, or would like to think I am.
After the first time using the sister machine, I was just a little sore and didn't think a whole lot of it.
But after I did it on Tuesday, I can hardly move my arm above my waist.
Flying might keep them young, but without a lot more building up, it's tearing me down.