Clinical perspectives regarding eccentric muscle injury.

Muscle strain injuries occur to predictable muscles at consistent locations during expected sporting maneuvers when a muscle is stretched and then activated, particularly during high intensity bursts of activity. More than 30% of the injuries seen in the clinician's office are injuries to skeletal muscle. The typical location of the injury is just proximal to the distal muscle tendon junction regardless of strain rate or architecture of the muscle. After the injury, the muscle is weaker, continues to weaken, then recovers during the next week. An inflammatory response is seen in the following 1 to 2 days. By the seventh day, fibrous tissue replaces the inflammatory reaction and a scar forms. When a muscle is stretched, its tension still is reduced making the healing muscle more susceptible to a repeat injury. Viscoelastic properties of muscle also can help explain how muscle can be protected against strain injury. A 1 degree C increase in muscle temperature (warm-up) increases the muscle length to failure and a fatigued muscle is more susceptible to strain injury. It probably is impossible to prevent muscle strain injury; however, preventive measures can make muscle more resistant to these stretch-induced injuries.