Is there anything that can replace running for conditioning. I just don't think my knees/joints can take it anymore. It's gotten worse since I have put on about 10lbs. of mass recently. Right now, I do bjj 3x per week and boxing 3x per week. Could I just do like 30 minuntes of skipping instead of running or maybe the bas rutten mma workout? I don't have access to a pool and I suck at swimming anyways. Thanks for any advice.