The posterior deltoid (L. posterior, behind ; deltoides, triangular) refers to the rear head of the three-headed deltoid muscle. It acts on the shoulder joint and is the prime mover in shoulder horizontal abduction. Located on the back of the shoulder – medial to the lateral deltoid and lateral to the middle trapezius – the posterior … Read more

The erector spinae (erigere, to erect ; spina, spine.) consists of three long, thin muscle groups running vertically up each side of the vertebral column: the iliocostalis, longissimus and spinalis. These muscles act on different segments of the vertebral column (i.e. lumbar, thoracic, cervical). Collectively, they are the prime movers in spinal extension and spinal … Read more

The internal oblique (L. internus, internal ; obliquus, oblique.) is a flat sheet of muscle on either the side of the lower torso. It gets its name from being beneath the external oblique and having an oblique fiber direction relative to the midline. The most prominent actions of the internal oblique are spinal lateral flexion and spinal rotation. Notably, … Read more

The lateral deltoid (L. latus, side ; deltoides, triangular) is the outermost head of the deltoid and is primarily responsible for performing shoulder abduction. The lateral deltoid is part of the scapulohumeral (intrinsic shoulder) muscle group. It is situated between the anterior and posterior deltoid, and lies superficial to the insertions of the supraspinatus, infraspinatus and teres minor. It originates from the acromion process on … Read more

The anterior deltoid (L. anterior, before, in front of ; deltoides, triangular) refers to the front head of the deltoid muscle. This part of the delt is responsible for shoulder flexion. Classified as part of the scapulohumeral (intrinsic shoulder) muscle group, the anterior deltoid is situated medial to the lateral deltoid and lateral to the clavicular head of … Read more

Literally meaning the three-headed muscle of the arm, the triceps brachii (L. tres, three ; caput, head ; brachium, arm.) consists of a long, lateral and medial head. It is primarily responsible for elbow extension. Known commonly as just the triceps, it is twice as big as its counterpart, the biceps brachii, and thus accounts for … Read more

As is made explicit by its Latin translation, the quadriceps femoris (L. quattuor, four ; caput, head ; femoris, femur.) literally means the four-headed muscle of the femur, or thigh. The four heads of the quadriceps femoris – or simply the quadriceps – include the following: rectus femoris, vastus lateralis, vastus intermedius and vastus medialis. The primary … Read more

The hip adductors refers to a group of five muscles that make up the bulk of the inner thigh mass. The primary function of this group is, surprise, hip adduction! The better known of the hip adductors are the adductor brevis, longus and magnus (L. ad, to ; ducere, to lead ; brevis, short ; longus, long … Read more

The pronator teres (L. pronus, lying face down ; teres, round and long.) is an elongated, cylindrical forearm muscle that crosses the gap between radius and ulna. It’s the strongest of the two pronator muscles. However, it is only active during rapid or resisted forearm pronation, which it carries out with help from the pronator quadratus. Notably, it also plays … Read more