ESSENTIALS: ANATOMY & PHYSIOLOGY

The wrist includes a complex aggregation of muscles that drive movement about its joints. The posterior muscles of the wrist are generally used for extension but in a few exceptions carry out an additional action. The wrist extensors are found on the posterior arm, opposite the flexors on the anterior side. These muscles can be attached proximally to the humerus, radius, or ulna and distally to the carpals, metacarpals, or phalanges.

The muscular structure of the wrist and hand is quite complex, reflecting the complexity of the tasks they perform.

The muscles on the back of the arm that oppose the roles of the anterior flexors are few in number, including only the triceps brachii and anconeus. These posterior muscles of the elbow are considered elbow extensors, increasing the angle of the humerus and the two bones of the forearm: the radius and ulna.

The elbow musculature is an integral part of an upper axillary system and is capable of both extremely refined and very powerful movement. The anterior muscles of the elbow are considered elbow flexors, reducing the angle of the humerus and the two bones of the forearm, the radius and ulna. If the upper and lower arm are aligned in extension at 180 degrees (straight), flexion will reduce that angle to about 30 degrees. As with other regions, the muscles are arranged in layers: superficial, intermediate, and deep.

Impingement refers to the impeding interaction of hard bony surfaces with softer muscular, connective, and neural tissues, causing pain. The conventional wisdom for the genesis of this syndrome is that the acromion process comes into contact with and impinges upon the tendinous underlying tissues. This is suggested to occur when the arm is lifted, bringing the humeral head and shaft into close proximity with the acromion. The idea is that this movement, when repeated over time, compresses and damages the softer tissues.

The arm is suspended, relative to the axial skeleton, with very little bony support. Instead, muscle, tendon, and ligament attach the arm to the thoracic architecture. This arrangement creates a great deal of mobility but also poses a problem with regard to joint stability in high-velocity or high-force conditions. The rotator cuff, therefore, is a popular topic in exercise and sports.

Every load carried, pulled, or pushed with the hands transmits its weight to the axial skeleton and then the ground through the shoulder skeleton and musculature. You can’t pull a weight off the ground without shoulder muscle contribution. You can’t push overhead without significant shoulder contribution. Even something as simple as holding a bag of groceries recruits the muscles of the shoulder.

The musculature of the shoulder joints is structured and oriented in a manner to provide mobility in every direction around the ball-and-socket joint. It also provides stability, given the relative lack of bony support in the joint.

There are three layers of posterior vertebral muscles overlaying the vertebral column, and each layer affects vertebral position in postural stability and movement. The anterior musculature is also organized in an approximation of a three-layer structure. When considering gross movement of the vertebral column, vis-à-vis arching and rounding, we often only think of the erector spinae as driving arching and the rectus abdominis as driving rounding. However, movement into those positions is complex and requires more than the action of the prime movers.

Many muscles act upon the lumbar vertebrae during anterior flexion, rotation, and lateral flexion. What we commonly refer to as abdominal muscles carry a major role in lumbar movement. Some of these muscles attach to and act directly upon the lumbar vertebrae. Others that are not attached to the vertebrae act indirectly through moving bones that are.

As with musculature in other segments of the vertebral column, the lumbar muscles have attachments in the segments above and below. These muscles contribute to respiration, posture, and the mobility of the vertebral column.

Many muscles in the thoracic segment contribute to respiratory function by moving the costals. Examples of this are the external and internal intercostals, which are found circumferentially around the thoracic cavity — posterior, lateral, and anterior. The transversus thoracis and diaphragm also contribute to respiration.

The thoracic segment of the body is home to the thoracic vertebrae, the ribs (costals), and numerous muscles that move the vertebral column, ribs, and structures attached to the thoracic skeleton. Deep muscles that arise and act primarily within the thoracic generally have contractile functions in respiration (breathing) and maintaining vertebral column posture.

The cervical vertebral skeleton serves as an attachment point for a large number of muscles, creating a complex set of moving connections between the skull, vertebrae, scapulae, clavicles, sternum, and ribs.

The cervical vertebral skeleton serves as an attachment for a large number of muscles that create a complex set of moving connections between the skull, vertebrae, scapulae, clavicles, sternum, and ribs.

Atrophy is a simple and opposing process to hypertrophy. Just as exercise can drive an adaptive increase in muscle mass, lack of exercise can cause a reductive adaptation or loss of muscle mass. As one would expect, the entire muscle may shrink in size such that it is easily and visually detectable, but atrophy occurs at every level of muscular organization, beginning with the molecular.

The physiological process of increasing the size of an entire muscle is known as hypertrophy. Human muscle has a huge capacity for hypertrophy and is able to increase in size by 200% or more. A person maintains this ability throughout his or her lifespan.

When muscles contract, the brain or a reflex mediated by the autonomic nervous system sends a signal out along a motor neuron (a nerve feeding information to a muscle). The neural signal hits the muscle cell, which triggers chemical events inside the cell. Those chemical events yield a binding of contractile proteins — actin to myosin — energy gets expended, myosin changes shape, causing sarcomere and cell shortening, and thus results in a production of force. No fewer than 20 muscle proteins and multiple other biochemicals are involved.

We often think of muscles only in the context of biceps, triceps, pecs, and quads, but to do so ignores the fact that there is more than one type of muscle cell in the human body. There are, in fact, three types of muscle cells: skeletal, cardiac, and smooth muscle cells. Skeletal muscle cells drive movement, cardiac muscle cells circulate blood, and smooth muscle cells move things like blood and waste through the vascular system and intestines.

Scoliosis involves the presence of abnormal curvatures along the vertebral column. The degree of scoliosis may vary dramatically from mild imperceptible curves to severe and physically perceptible deformations that limit movement capacity. Physicians diagnose any lateral deviation greater than 10 degrees from vertical as scoliosis. In the gym, it manifests as a hip or shoulder tilt when athletes should be maintaining a neutral position, level and parallel to the floor.