The upper arm
The upper limb consists of three main regions – the arm (from shoulder to elbow), the forearm (from elbow to wrist) and the hand.
The humerus is the longest and largest bone of the upper limb, and is the only bone in the arm. It articulates with the glenoid cavity of the scapula above, and with the radius and ulna of the forearm below.
The radius and ulna are two long slender bones, arranged in parallel, which can rotate around each other.
The joint between the humerus and ulna is a synovial hinge joint which works within a single plane of movement (the sagittal plane). Movements allowed are flexion and extension.
The joint between the humerus and the radius is a synovial pivot joint allowing movement within a single plane (the transverse plane). Movements allowed are pronation and supination.
The radius and ulna are connected to each other by a synovial joint at each end. This is known as the radio-ulnar joint (a pivot joint) that allows pronation and supination of the hand. They are also connected down their whole length by a fibrous, movable membrane (interosseous membrane).
In the anatomical position, the hand is supinated and the radius and ulna are parallel to each other. In pronation, the forearm rotates medially and the palm is moved to a posterior- or inferior-facing position. Pronation moves the distal end of the radius across the ulna so the two bones form an X. This is the forearm’s position when we are standing in a relaxed manner.
The radius and ulna join to the wrist. The ulna and the radius join two rows of 4 carpal bones at the wrist forming a synovial condyloid joint and allowing abduction (ulnar deviation), adduction (radial deviation), flexion and extension.
The palm of the hand consists of 5 metacarpal bones, which join with the phalanges of the thumb and fingers. Each of the fingers consists of 3 phalanges, and the thumb two phalanges, making a total of 14.
Hyperextension of the wrist can lead to Carpal Tunnel Syndrome, ligament damage and nerve compression. This is why the wrist should be kept relatively flat during exercise.
Carpal Tunnel Syndrome occurs when inflammation of the tendons and tendon sheaths presses on the median nerve going to the hand. This results in a persistent dull ache, especially at night, with pain and numbness radiating to the thumb and fingers.