At some point during physical activity, a muscle in the body is likely to come under more pressure than it is prepared to handle. The result is a painful sensation that may leave bruising on the body, and the muscle will feel tender and sore for days or even weeks. These injuries are commonly — and incorrectly — called muscle sprains. The proper name for such injuries is a muscle strain, as muscle sprains cannot occur; a sprain occurs when a ligament is overstretched or otherwise injured, whereas a strain occurs when a muscle is overstretched or injured.
This means that what people consider muscle sprains are either one of two things: a ligament sprain or a muscle strain. A ligament is a grouping of fibrous tissues that connect bones to other bones around joints in the body. Ligaments can also attach bone to cartilage, and when they become over-stressed by a sudden impact, an awkward twisting motion, or the sudden application of weight, they can become what many people believe to be muscle sprains. In reality, it is actually a ligament sprain, and the muscles may be entirely unaffected. Ligament sprains tend to take more time to heal than muscle strains, though the two injuries are generally treated similarly.
Muscle strains are the proper term for what many believe to be muscle sprains. A muscle can be strained anywhere in the body for a variety of reasons, but the most common muscle strains occur in the legs, back, and neck. Athletes are very likely to strain a muscle during or after exercise, especially if the athlete has not properly conditioned his body for the athletic activity. When participating in a new activity that has muscles moving in ways they are not used to, the muscles are likely to tire quickly, raising the likelihood of a muscle strain.
Simply over-stretching a muscle can cause a muscle strain as well. If the muscle stretches well beyond its normal limits, the muscle can even tear. Such injuries require the RICE treatment — Rest, Ice, Compression, and Elevation — and can take several days to several weeks or months to heal. In more severe cases, muscle tears may have to be treated surgically, but in most cases, resting and light stretching should help alleviate the pain and encourage healing in the damaged muscle. Stretching before and after exercise also helps prevent muscle strains, as does drinking plenty of water before, during, and after exercise.