Muscle fatigue and pain.

Muscle fatigue and pain are together common symptoms which can be analysed physiologically. For many patients attending a medical clinic the problem for the doctor is to decide whether the problem is "in the mind" or "in the muscle". A history of the symptoms occurring at rest without any exercise is a hint of psychological origin. Exercise fatigue or pain should ideally be reproduced by an appropriate provoking exercise test. Needle biopsy with histochemistry is cost-effective as a means of reaching a diagnosis while blood determinations of erythrocyte sedimentation rate and plasma creatine kinase and lactate are more specific but less sensitive indicators of a muscle cause. Fatigue is analysed by force and action potential measurements with electrically stimulated contractions. Pain worse after exercise can be related to muscle damage. A programme of therapeutic exercise may be tried as a further means of assessment of these symptoms.