A strain (also known as a pulled muscle) is caused by a sudden movement that the body is unprepared for, where the muscle and tendon stretch beyond their normal limits, and tear. The dog may display discomfort, the area may become swollen, and in severe strains, the muscle tears completely and will need surgery to repair.
The first 3 days following injury, the pain and swelling are intense. As the body repairs itself, laying down new tissue and developing scar tissue, mild exercise can strengthen the damaged area, but care must be taken not to inflict more damage to the fragile scar tissue.
From around 3 – 6 weeks onwards, the muscle becomes stronger as the muscle fibres strengthen. Care should still be taken to avoid further damage, as the scar tissue is weaker and less flexible than the original muscle. Damaged scar tissue could set recovery back. There is also a possibility that the scar tissue may form a bulky mass.