Originally Posted by smokes
Damn that looks like it could go so wrong

Are you suggesting those for back/core replacement exercises? I could try it with my dumbbells.... Extremely carefully haha...

BTW, do you think 30min-1hr playing basketball 1 on 1 or just solo is suitable cardio? I'm not a big fan of running (knees again).
Kettlebells swings are great for your back and legs.

Cardio is non stop aerobic activity, but since you're trying to gain mass; playing ball would be fine. You just need 15-25 minutes of cardio.