a couple of years ago I made a big mistake.
I used to take a long backswing on a forehand drive. After a coach pointed out that the backswing was too long, I decided to do two things. First, I moved the table closer to the garage roll-a-door, so that if I took a big backswing I would hit my bat against the door. This idea could well have helped, but the next thing caused the damage.
Using a robot, I set it to deliver topspin balls to my forehand, for about 15 minutes, on a high ball-frequency. I reasoned that if I could keep returning the balls successfully, that would eliminate the big-backswing problem. That was the mistake. The result was that I got injured, getting a rotator-cuff shoulder injury. I think that's what the physio called it. I had an x-ray and the damage could be seen by the doctor. There was some fluid in my arm, which indicated the damage. At this stage my arm felt weak and dead. I went to the physio and got one treatment each week for several weeks. Unfortunately, each treatment would only last one day. I tried to play some competition, but didn't have strength or sensation in my arm for forehands. The only thing that fixed me was time - about a year! This was very frustrating. I hope this is a warning to other players.
Recently, I have been trying to achieve some topspin on my forehand, and have hit hundreds of balls around the garage, studying the spin when they hit the ground. Unfortunately, my arm is feeling weak again, the first symptoms of the injury 2 years ago. It seems that I'm over-training again. I've taken a small break and hope it doesn't get worse.
I'm wondering if I have a weak arm in general, and also whether it would be good to do some basic weight training (eg lifting a 1kg weight). The physio told me to do weights, which I did for a while but they didn't seem to help. I guess I should also be trying to use my legs to generate power, and take pressure off my arm. How do you become a great player without getting injured in training?