Juggling for cardio training

As I'm unable to run because of my shin injury, and have no working bicycle, my training plan has been reduced to strength training, walking and juggling.

I have found that if I spend a good hour juggling to music and doing tricks of various kinds, it can be quite a cardiovascular workout. Last night I was working on juggling three beanbags with one arm behind my back. After about 10 minutes of trying this on both side, I collapsed onto the couch, my heart racing like I had just run intervals at the track. Later on, working on 5-ball endurance and 5-ball half-showers, I found myself out of breath again.

So either I'm getting really out of shape, or juggling can be great cardio exercise.