A charley horse is a term for a painful contusion (bruise) of the quadriceps muscle of the anterior or lateral thigh that commonly results in a muscular hematoma and sometimes several weeks of pain and disability. It often occurs in sports when an athlete is struck by an opponent's knee, in a manner like the kick of a horse, perhaps the reason for its name. In the UK and many Commonwealth countries, such an injury is known as a dead leg. This can be very painful and happens only in the leg area. In Australia this is also known as a corked thigh or "corkie".

"Charley horse" is also used to describe leg/foot cramping, especially those that follow strenuous exercise. These muscle cramps can have many possible causes including hormonal imbalances, dehydration, side effects of medication, or more seriously, diseases such as amyotrophic lateral sclerosis and neuropathy. They are also a common complaint during pregnancy.It could also be as simple as not enough magnesium or potassium, or too much calcium.

Treatment

The quadriceps contusion type of "charley horse" is initially treated by icing. Recent studies have shown that the resulting tightness and contractions that sometimes ensue can be lessened by maintaining the knee in a fully bent position for the first 24 hours to prevent the involved muscles from going into spasm. Prematurely returning to sports activities increases the likelihood of the main complication of a charley horse, the deposition of calcium into the hematoma that forms at the site of injury. This complication, termed myositis ossificans, can result in long-term disability.

A cramp can be quickly defused with active stretching of the affected muscle. Cramps in the calf muscle can be defused by outstretching the leg, pushing the heel downward, and pointing your toes toward your head. Standing up with most of your weight on the ball of the foot on the cramping side will also stretch the gastrocnemius muscle and diffuse the pain. If you feel a cramp starting, this will usually stop it from becoming more painful. Persistent cramps should be treated by a doctor.

Etymology

The term may date back to American baseball slang of the 1880s, possibly from the pitcher Charlie "Old Hoss" Radbourn who is said to have suffered from cramps. Another story mentions a horse named Charley that used to work at Comiskey Park, the Chicago White Sox's ballpark. In those days, an old, retired horse was often called "Charlie".

The term may also reference Charlie "Bucket" McCormick, who was said to wander the streets of Altoona in the late 1800s and massage the calf muscles of the horses who would deliver bushels of rye to local Shriners. The Shriners used this rye for bootleg whiskey, and so the horses needed to have strong calf muscles to outrun the tax collecting authorities.Fact: date=September 2008

In Norway it is commonly known as a lårhøne (thigh hen), while it in Denmark is known as a trælår (wooden thigh).