When girthing up the horse it is important not to over tighten it. An over-tightened girth may pinch and bruise the muscles – in particular the pectorals. trapezius, serratus ventralis muscles and latissimus dorsi (see red areas in diagram below). An over tightened girth may also cause bruising of the ribs and the intercostal muscles between the ribs. It will also cause the saddle to put more pressure on the back muscles.