muscle strain

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An injury in which a muscle is damaged by being excessively stretched or overworked. It may result from a direct impact that pushes the muscle against an underlying bone. However, many muscle strains in sport are distraction strains, which occur when a muscle accidentally contracts as it is being stretched. They are relatively common in those who attempt to do vigorous exercise without a sufficient warm-up, or in those suffering fatigue and impaired reflexes. The strains may be slight, causing little discomfort and swelling (first degree strain); they may be quite painful but with no muscle tear (second degree strain); or they be very painful and involve a complete tearing of the muscle when the muscle is stretched beyond its tolerance levels (third degree strain, or distraction rupture). Muscle tears most commonly affect muscles that span two joints. For example, contractions of the hamstring cause the knee and hip to move in opposing directions, normally at different times but if both actions occur simultaneously there is a high risk of a muscle tear. See also muscle soreness.

When unclassified, a muscle strain usually refers to a relatively minor injury in which muscle fibres are damaged, but there is little if any rupture of blood capillaries. However, a strain is usually classified as a first, second, or third degree strain according to the severity of damage to the muscle. A first degree strain refers to tearing of less than 25% of the muscle fibres the muscle is tender, but there is usually no impairment of muscle action. A second degree strain refers to tearing of between 25 and 75% of the fibres, usually accompanied by swelling and bruising, and some limitation of muscle mobility. A third degree strain refers to a complete rupture of the fibres with the muscle being completely torn in two; it is accompanied by extreme tenderness, severe bruising (see haematoma) and impairment of movement. Rest, ice, compression, and elevation (see RICE) is the cornerstone of primary treatment. Ice should be applied immediately after the injury (see ice treatment). A doctor should be consulted if function is impaired. Mild and moderate strains often benefit from light stretching within the pain threshold. Strains, tears, and ruptures most commonly affect those muscles, such as the hamstrings, which span two joints (see Lombard's paradox). They occur most often in cold weather when joints are stiff and coordination is impaired by nerve conduction being slow. Wearing suitable clothes and warming-up adequately can reduce the risk of muscle strains. See also muscle soreness.