If you have injured the muscles or tendons that attach to the upper part of your back behind your chest, this injury is called a thoracic strain, thoracic sprain, or mid-back strain. The cause of thoracic strain varies.
A less severe injury involves pulling a muscle or tendon without tearing it. A more severe injury involves tearing (rupturing) a muscle or tendon. With less severe injuries, there may be little loss of strength. Sometimes, there are breaks (fractures) in the bones to which the muscles are attached. These fractures are rare unless there was a direct hit (trauma) or you have weak bones due to osteoporosis or age. Longstanding strains may be caused by overuse or improper form during certain movements. Obesity can also increase your risk for back injuries. Sudden strains may occur due to injury or not warming up properly before exercise. Often, there is no obvious cause for a thoracic strain.