if you get hurt practicing it's because you lack technique.. I mean, every pianist should play in complete muscular repose
I don't agree with the school of thought that you should be relaxed absolutely all of the time-there has to be some action of the muscles for the action to happen. The key is quick relaxation. Relaxation is going from a state of action to a state of repose, not staying in a state of repose.
Although it is true that good technique is not 100% relaxed 100% of the time, I have never in my life seen someone who was having technical issues related too MUCH relaxation.