Origin: The spine of the scapula.
Insertion: into the deltoid tuberosity of the humerus.
Function: The deltoid is mainly responsible for flexion of the shoulder joint and can also aid in abduction of the shoulder. This makes it an important contributor to stride length.
Soreness: If there is tightness or discomfort in this area, the horse may have a shortened stride. The horse may also move away from palpation over the shoulder or stomp the forelimb.
Massage can relieve tension and discomfort in this muscle, whilst stretching exercises such as lifting the forelimb forward and extending the shoulder can help to stretch the deltoid muscle as well as other shoulder and forelimb muscles on a more regular basis. Good flexibility at the shoulder is important for jumpers to achieve good scope over the fence.