BB I seen on tv Japanese men in their 70's who do weight training & they looked "SUPER". (looked 25 yrs younger) They used lighter weights so it was not too hard on their joints so they said.
I've done weights since I turned 18 because every sport that I did that was part of it. Sometimes it was for endurance, and other times it was for power or for strength depending on what sport I was focussing on at the time. My last stint for training with heavy weights for strength and power was through my late thirties and right up to my mid forties because I was seriously training to be a better, faster sprinter (200m, 400m). I didn't think I was "there" unless I could bench 100 lbs. over my body weight or twice my weight for a squat. At age 45 I was as strong as I have ever been through out my life.
But due to a couple of injuries and surgeries not related to training in the gym I've totally had to give up doing heavy weights. A big part of it is because of my age. I don't doubt for a second that a good part of my shoulder pain and some of my knee discomfort has come from lifting heavy, as BB has suggested, but for me I think my joints are in the condition they are is because of all the wear and tear due the hard core activities I've participated in over the last 40+ years.....hockey, lacrosse, freestyle skiing (blew out my knee the first time there), flying over my handle bars far too many times to even count mountain biking, teaching approx. 2500 fitnesss classes, ten years of triathloning, 20 years of road running, and 12 years sprinting....even fishing 75+ days per day.
They all took their toll but I wouldn't have wanted to give up on any of those things despite having a beaten up body. I definitely have some arthritis in both shoulders, some calcification of the tendons running through the joint capsules in both shoulders and some bursitis. Could have probably avoided a lot of that with better warmups. When you're young you think you can just walk into a gym, throw a couple of 45's on and just start banging off reps. I'm sure if I was to do the same warmup I've been having to do for the last 8 years I wouldn't have a lot of that joint discomfort and wouldn't be on a daily dose of celebrex. Since we bought our cabin 5 years agop I've given up on competing. Would rather fish every weekend instead of going to track meets.
Besides I'm kind of burnt out. Just keeping reasonably fit by my standards doing "school girl" weights. Any more than that causes too much irritation to my joints. I still train 6 days a week but I now I train smarter not harder....even though, I still have a lot of aches and pains so I could be a lot "smarter" yet!
So for all you guys who are gung ho to lose weight, get fit, and hit the gym, pay heed especially if you're over 40 and haven't been on a regular exercise program. Get in a good warm up! It takes muscle tendons 6 times longer to catch up with muscle strength so take it slow over the next few months....otherwise you'll have to suffer through tendonitis, bursitis, and sorer muscles than you need to. As Brian said, going too heavy just because you think you can will takes it's toll on the body. You can get a good level of fitness just by exercising regularly with lighter weights and more reps.....just takes a litttle longer is all. It's all worth it in the end!