Muscle pain and weakness can persist for an extended period of time following illness, particularly those of an infectious nature. Also referred to as post-infectious disease syndrome, this set of symptoms includes muscle fatigue and weakness—which may or may not be accompanied by pain—occurring for several hours or even several days after the illness has passed. These symptoms seem to affect the leg muscles in particular, although the upper arms and back are also commonly involved. In addition to muscular pain, those affected by this condition may experience neurological symptoms such as mental exhaustion, poor concentration, blurred vision, and headaches. Some people affected by post-illness muscle pain also may experience a tingling sensation in the limbs or face as well as a feeling of coldness in the limbs. Despite the wide variety of symptoms, there are not many physical signs associated with this condition, and those that do manifest are often subtle. Information regarding the cause of post-illness pain is limited, though some studies suggest it is more common in certain types or strains of infection. Allergy and host susceptibility may also play a role. Treatment may include monitoring for signs of secondary infection, administering pain relief medications and mechanisms, and physical therapy to promote muscle repair and stimulate blood flow.