 If an underlying muscle disease is suspected , for instance if there is no obvious explanation or there have been multiple episodes , it may be necessary to perform further investigations . During an attack , low levels of carnitine in the blood and high levels of acylcarnitine in blood and urine may indicate a lipid metabolism defect , but these abnormalities revert to normal during convalescence . Other tests may be used at that stage to demonstrate these disorders . Disorders of glycolysis can be detected by various means , including the measurement of lactate after exercise ; a failure of the lactate to rise may be indicative of a disorder in glycolysis , while an exaggerated response is typical of mitochondrial diseases . Electromyography ( EMG ) may show particular patterns in specific muscle diseases ; for instance , McArdle 's disease and phosphofructokinase deficiency show a phenomenon called cramp @-@ like contracture . There are genetic tests available for many of the hereditary muscle conditions that predispose to myoglobinuria and rhabdomyolysis . 
