A strain (also known colloquially as a pulled muscle or torn muscle) is an acute or chronic soft tissue injury that occurs to a muscle, tendon, or both (contractile components). The equivalent injury to a ligament is a sprain.
Typical signs and symptoms of a strain include pain, functional loss of the involved structure, muscle weakness, contusion, and localized inflammation. A strain can range from mild annoyance to very painful, depending on the extent of injury.
A strain can occur as a result of improper body mechanics with any activity (e.g., contact sports, lifting heavy objects, overstretching) that can induce mechanical trauma or injury. Generally, the muscle or tendon overstretches and is placed under more physical stress than it can exert.  Strains commonly result in a partial or complete tear of a tendon or muscle, or they can be severe in the form of a complete tendon rupture. The most common body location for strains to occur is in the foot, leg, or back.
Degrees of Injury (as classified by the American College of Sports Medicine) 
• First degree (mildest) – little tissue tearing; mild tenderness; pain with full range of motion.
• Second degree – torn muscle or tendon tissues; painful, limited motion; possibly some swelling or depression at the spot of the injury.
• Third degree (most severe) – limited or no movement; pain will be severe at first, but may be painless after the initial injury
Although strains are not restricted to athletes and can happen while doing everyday tasks, however, people who play sports are more at risk for developing a strain. It should also be noted that it is common for an injury to develop when there is a sudden increase in duration, intensity, or frequency of an activity.
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Immediate treatment is usually an adjunctive therapy of NSAID's and Cold compression therapy. Controlling the inflammation is critical to the healing process. Cold compression therapy acts to reduce swelling and pain by reducing leukocyte extravasation into the injured area. NSAID's such as Ibuprofen/paracetamol work to reduce the immediate inflammation by inhibiting Cox-1 & Cox-2 enzymes, which are the enzymes responsible for converting arachidonic acid into prostaglandin. However, NSAIDs, including aspirin and ibuprofen, affect platelet function (this is why they are known as "blood thinners") and should not be taken during the period when tissue is bleeding because they will tend to increase blood flow, inhibit clotting, and thereby increase bleeding and swelling. After the bleeding has stopped, NSAIDs can be used with some effectiveness to reduce inflammation and pain.
It is recommended that the person injured should consult a medical provider if the injury is accompanied by severe pain, if the limb cannot be used, or if there is noticeable tenderness over an isolated spot. These can be signs of a broken or fractured bone, a sprain, or a complete muscle tear.