Yeah, the rope has weight and I don't get nearly as tired (or really, tired at all) when I do jumping jacks as when I skip rope. It's harder the faster you go because the rope wants to get out of control... and you're not even making big jumps when you get good at it. Plus, I tend to pound the ground a lot harder doing jumping jacks than when I'm skipping rope (probably to compensate for the missing resistance from the rope) and that really kills the joints.
Just get a rope. It's not that expensive and the results will be much better. Now that you brought it up, I think I'm going to start jump-roping again, too!
