Torn ACL and 30 Day Shred

surpanakha

I'm sorry if a topic regarding this has already been started. It is my first time to post in the forums. You see, I had an ACL reconstruction surgery back in December, and gained 15 lbs because I could not walk for some time and had nothing to do but eat. I have recently lost 7 of those 15 lbs, but I am afraid to do any cardio exercises that involve jumping or running (basically, any cardio with high impact on the knees). However, I want to do circuit training, and do the 30 Day Shred again because I want to be toned as I lose more weight. Also, it has worked wonders for me before I got my operation. Jillian's cardio in the Shred, however, involves an awful lot of jumping and running in place. I want to do her strength and ab exercises but I'm afraid leaving out the cardio part would not make it a complete circuit training. What low impact cardio exercises can I substitute for the cardio in the 30 Day Shred?