Physiology

The text Anatomy & Physiology, (Marieb & Hoehn, 2013), states that like anatomy, physiology has many subdivisions. Most of them consider the operation of specific organ systems.  For example renal physiology concerns kidney function and urine production.  Neurophysiology explains the workings of the nervous system.  Cardiovascular physiology examines the operation of the heart and blood vessels.  While anatomy provides us with a static image of the body’s architecture, physiology reveals the body’s dynamic and animated workings.

Physiology also rests on the principles of physics, which help to explain electrical currents, blood pressure, and the way muscles use bones to cause body movements, among other things.

Movements Allowed by Synovial Joints

As described in the article on Anatomy, every skeletal muscle of the body is attached to bone or other connective tissue structures at no fewer than two points.  The muscle’s origin is attached to the immovable, or less moveable, bone.  Its other end, the insertion, is attached to the movable bone.  Body movement occurs when muscles contract across joints and their insertion moves toward their origin.  The movements can be described in directional terms relative to the lines, or axes, around which the body part moves and the planes of space along which the movement occurs, that is, along the transverse, frontal, or sagittal plane.

Range of motion allowed by synovial joints varies from non-axial movement (slipping movements only, as there is no axis around which movement can occur) to uniaxial movement (movement in one plane) to biaxial movement (movement in two planes) to multi-axial movement (movement in or around all three planes of space and axes).  Range of motion varies greatly in different people. In some, such as trained gymnasts, or karate-ka, range of joint movement may be extraordinary due to the amount of stretching they have subjected their bodies to.

There are three general types of movements: gliding movements, angular movements and rotation.

Gliding Movements

Gliding occurs when one flat, or nearly flat, bone surface glides or slips over another (back and forth and side to side) without appreciable angulation or rotation.  Gliding occurs at the intercarpal and intertarsal joints (hand and foot bones), and between the flat articular processes of the vertebrae.

Angular Movements

Angular movements increase or decrease the angle between two bones.  These movements may occur in any plane of the body and include flexion, extension, hyperextension, abduction, adduction, and circumduction.

 Flexion is a bending movement, usually along the sagittal plane, that decreases the angle of the joint and brings the articulating bones closer together.  Examples include bending the forearm towards the shoulder and bending the knee.

Extension is the reverse of flexion and occurs at the same joints.  It involves movement along the sagittal plane that increases the angle between he articulating ones and typically straightens a flexed limb or body part.

Abduction is the movement of a limb away from the midline or median plane of the body along the frontal plane or, to the side.  Raising the arm or leg laterally is an example of abduction.  For the fingers and toes, this means spreading them apart.

Adduction is the opposite of abduction, so it is the movement of a limb toward the body midline or, in the case of the fingers and toes, toward the midline of the hand or foot.

Circumduction is moving a limb so that it describes a cone in space (circum = around; duco = to draw).   The distal, or far, end of the limb moves in a circle, while the point of the cone (shoulder or hip joint) is more or less stationary.  Because circumduction consists of flexion, abduction, extension, and adduction performed in succession, it is the quickest way to exercise the many muscles that move the hip and shoulder joints.

Rotation is the turning of a bone around its own long axis.  It is the only movement allowed between the first two cervical vertebrae and is common at the hip and shoulder joints.  Rotation may be directed toward the midline or away from it.  For example, in medial rotation of the thigh, the femur’s anterior surface (the surface furthest from the midline) moves toward the median plane of the body.  Lateral rotation is movement in the opposite direction.

Special Movements

Certain movements do not fit into any of the categories described above and only occur at a few joints.

Supination and Pronation.   The terms supination, turning backward, and pronation, turning forward, refer to the movements of the radius around the ulna.  In layman’s terms, when you rotate your forearm so that the palm of your hand is facing down, or back, your hand is said to be in a pronated position. When you rotate the forearm so that the palm of your hand is facing up, or out, your hand is said to be in a supinated position.

Dorsiflexion and Plantar Flexion both refer to the up and down movements of the foot.  Lifting the foot is called dorsiflexion and depressing the foot is plantar flexion.

Inversion and Eversion refer to movements of the foot.  During inversion, the foot moves at the ankle so that the sole of the foot moves toward the midline of the body.  In eversion, the foot ‘rolls’ in the opposite direction, i.e. away from the midline.  Many shoe retailers will mistakenly, and incorrectly, substitute supination and pronation for these terms.

Levers – Bone/Muscle Relationships

The operation of most skeletal muscles involves leverage; using a lever to move an object.  A lever is a rigid bar that moves on a fixed pivot known as a fulcrum, when a force is applied to it.  The applied force, or effort, is used to move a resistance, or load.  In the body, the joints are the fulcrums and your bones act as levers.  Muscular contraction provides the effort that is applied at the muscle’s insertion point on a bone.  The load is the bone itself, along with overlying tissues and anything else you are trying to move with that lever, e.g. holding a barbell and lifting it by bending the elbow.

Levers: Power versus Speed

A lever allows a given effort to move a heavier load, or to move a load farther or faster, than it otherwise could.  If the load is close to the fulcrum, a small effort exerted over a relatively large distance can move a large load over a small distance.  Such a lever is said to operate at a mechanical advantage and is commonly known as a power lever.  For example, a person can lift a car with a power lever, or a jack.  The car moves up only a small distance with each downward push of the jack handle but relatively little muscle effort is needed.

On the other hand, when the load is far from the fulcrum and the effort is applied near the fulcrum, the force exerted by the muscle must be greater than the load to be moved or supported.  This lever system is known as a speed lever and operates at a mechanical disadvantage.  Speed levers are useful because they allow a load to be moved rapidly over a large distance with a wide range of motion.  Using a shovel is a good example.

 

Next time, we move on to your Strength Training Plan.