1 Service Details Priority Mail ExpressÂ® Overnight Guarantee1 Delivering 7 days a week, this is our fastest domestic service for time-sensitive letters, documents, or merchandise. 2  Guaranteed overnight scheduled delivery to most locations2, including PO Boxes, or your money back1. 3  From $13.09 online.
Freebase(4.82 / 22 votes)Rate this definition: Muscle pain. Myalgia, or muscle pain, is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections.
Introduction. A muscle cramp is a sudden, involuntary, painful contraction of a muscle or part of it, self-extinguishing within seconds to minutes and is often accompanied by a palpable knotting of the muscle.The cramp contractions are associated with repetitive firing of motor unit action potentials. cramp can be distinguished from spasms (i.e., any involuntary and abnormal muscle contraction, regardless of whether it is painful) or generic painful contractions based on clinical and electrophysiological criteria. For example, muscle contractures resemble cramps because they are involuntary and painful.