Violin, viola, cello, bass, harp, classical guitar and electric guitar

For string based musician's the biggest culprit to pain is in the way they hold the instrument and the posture assumed while playing. For example, most violinists support their instrument between the left shoulder and chin. The shoulder is elevated and the chin anchors down to the left to allow the left hand to move over the fingerboard. This continuously contracted position causes major neck and shoulder pain, stiffness and various muscle and joint dysfunctions. The most common is first and second rib dysfunction - which essentially chokes the blood supply, nerves and tissues of the neck, torso and arm pathways. 

Guitarists, bass and harp players will suffer back and neck pain due to their static sitting posture while in a twisted bent position. Electric guitars are usually supported by a strap over the neck and shoulder, that combined with a rounded shoulder position to strum further chokes the nerves of the neck, shoulder and upper arm. The pain caused can then lead to problems with the elbow, such as ulnar neuropathy and tendinitis. Working further down the arm to the hand, these problems of posture and support then contribute to the faulty alignment and weakening of the wrist and fingers.  

Maintaining healthy, strong and supple muscle tissue along these channels play a huge role in the longevity and efficiency to play these types of instruments well and be pain-free.