As long as you are not putting an excess of weight more than the joint can hold, it will be good for the joint as apposed to bad, no matter how many repetitions. Some thing to stay away from is impacts, those can damage joints pretty bad, and I know because when I did martial arts, the constant kicking and punching of either the bag or my sparring partners would wreck havoc on my joints. My elbows and knees are pretty fucked up even now, and have tendinitis in my left arm. Just started low dose test/hgh/igf-1/mgf with training mainly at the pool, for the next few weeks to fix everything up. I'm hoping for the best.