I tend to be wound tight, and am not naturally coordinated (like an athelete). I think I have decent technique, and I have had in-person lessons in the past. My problem is that my left shoulder, arm, wrist, and eventually fingers become quite stiff while playing for extended periods. When playing live, depending on the song, I may even become fatigued before we are through! I know it is because I am becoming quite tense, and my muscles are locking one at a time. Cycling like this for five or so songs, and I am quite spent, and my left hand starts feeling weak. Any advice on learning to relax??