Statins are a class of drugs given to lower cholesterol. Although statins are considered to be generally safe, some studies show that about 10% of people on statins develop muscle-related symptoms, from fatigue (tiredness), weakness, cramping, pain and sometimes a lifethreatening muscle breakdown condition known as rhabdomyolysis. In some, these symptoms may greatly affect their daily activities. One consideration why symptoms develop in only some patients is that they may have an underlying problem in the way their muscles use fats to produce energy. In these patients, the muscles are not able to fully utilize fats and so they become tired more easily. Fat within the muscle can also affect how your body uses a hormone called insulin, which affects your blood sugar levels. The investigators are specifically interested in previous statin users and determine if the muscle symptoms are related to changes in energy and sugar use. We propose to enroll patients who have developed muscle side effects on previous statin treatment and have since discontinued statin treatment.