Shoulder muscle strength, endurance and electromyographic fatigue in ankylosing spondylitis.

Shoulder muscle performance was tested in 8 working ankylosing spondylitis (AS) patients and compared with 10 healthy male referents. The AS patients were all in a non-active state and had no shoulder symptoms. Electromyographic fatigue development in the descending part of the trapezius muscle was significantly faster in the AS group during an endurance time test than in the referents. This indicates a change in muscle function consistent with previous reports of myopathy in AS patients. There were no significant differences in shoulder forward flexion strength, endurance time or recovery of endurance time between the AS patients and the referents.