Start practicing more each day until you are playing longer than the opera will last each day.
Work up to it a little each day. if you do an hour a day now do an hour an 10 mins for a week then go to an hour and 20 mins, and, so on.
At first play long note scales that will build your strength up. Several seconds each note. I know yuck! It has to be done.
You might look for some hints about music related injuries on the web. I know Stings just had an artical about this topic.
Your topic is someting that struck home to me. I have a dear friend that had played 23 stright years in a community orchestra and had to sit out this spring because of a sholder injury - rotator cuff.
And you did not think you were a pro jock did you!
