The upper limb is a marvel of evolutionary engineering, designed for both powerful lifting and delicate, precise movements. Its muscles are organized into four main anatomical regions: the shoulder, the arm, the forearm, and the hand. Unlike the lower limb, which is built primarily for stability and weight-bearing, the upper limb prioritizes mobility. Midwives rely heavily on their upper limbs during clinical duties—from supporting a laboring mother to performing newborn resuscitation. Understanding how these muscles originate, insert, and act helps clinicians prevent repetitive strain injuries and properly assess neurological deficits.
Superficial back muscles bridge the axial skeleton to the appendicular skeleton, anchoring and moving the pectoral girdle.
The shoulder region creates a bridge between the trunk and the arm, providing a wide range of motion. The deltoid muscle forms the rounded contour of the shoulder and is the primary abductor of the arm beyond the initial 15 degrees. Deep to the deltoid lies the rotator cuff, a group of four stabilizing muscles (Supraspinatus, Infraspinatus, Teres minor, and Subscapularis, remembered by the mnemonic SITS). These muscles hold the head of the humerus firmly within the shallow glenoid cavity during arm movements. On the anterior chest wall, the pectoralis major and pectoralis minor pull the shoulder forward and downward, assisting with deep breathing and arm adduction.
The arm (stretching from shoulder to elbow) is divided by deep fascial planes into an anterior (flexor) compartment and a posterior (extensor) compartment.
Forearm musculature is complex, controlling movements of the wrist, hand, and fingers, as well as the twisting action of pronation and supination. The anterior forearm houses flexors and pronators, mostly originating from the medial epicondyle of the humerus and controlled largely by the median and ulnar nerves. Conversely, the posterior forearm houses extensors and supinators, originating around the lateral epicondyle and driven by the radial nerve. Tendons from these forearm muscles travel through the wrist into the hand, acting like puppet strings to move the fingers without needing bulky muscles inside the hand itself.
Intrinsic muscles are entirely contained within the hand, responsible for fine motor control and intricate adjustments of grip. They are organized into distinct groups:
Upper limb muscles and their supplying nerves are vulnerable to trauma, compression, and repetitive strain. Midwives should be aware of conditions like Erb's palsy (brachial plexus stretch injury during difficult shoulder dystocia deliveries, leading to the classic 'waiter's tip' posture) and carpal tunnel syndrome (median nerve compression causing numbness and thenar muscle wasting). Ergonomic awareness during clinical practice helps prevent work-related musculoskeletal disorders in the shoulders and wrists.