Chapter Three... Kinesiology of the Dog


  • Kinesiology is the study of motion and of the structures that make motion possible. This section is for you to use to identify the muscles involved when your animal you are caring for experiences specific problems. First, here's a list of some of the terminology that will be used.

    Protraction: the forward motion of the legs.

    Retraction: the backward motion of the legs.

    Abduction: outward motion of the legs.

    Adduction: the inward motion of the legs.

    Isometric Contraction: this occurs when a muscle contracts without causing an obvious movement. The best example is when a dog stands on a moving platform, like the on back of a truck, and has to adjust his muscle distribution to remain standing.

    Concentric Contraction: this occurs when the muscle shortens as it contracts and induces articular (joint) movements, such as those seen in pro traction, retraction, abduction, and adduction movements.

    Agonist Muscle: when a muscle contracts it is referred to as the agonist muscle responsible for the concentric contraction.

    Antagonist Muscle: the muscle that counteracts the agonist action is referred to as the antagonist muscle. It is elongated during the concentric contraction and is often, but not always, responsible for eccentric contraction.

    Eccentric Contraction: this takes place when a contracted antagonist muscle releases from its contracted state slowly to allow for better muscle control. Such a contraction permits movement to be slowed down at will. This action avoids jerky movements and allows for elegance and suppleness in the dogs movement. And eccentric contraction also acts as a shock absorber, a very important attribute during landing or any other such abrupt movement.


    How a Dog Moves
    To understand how a dog moves, we need to be aware of the interplay between bones, joints, ligaments, tendons, and muscle groups that makes the movements possible. A dog's hind legs provide the driving force and the power for the movement of the body. The forelegs are more concerned with direction and shock absorption. Muscles are always arranged in opposite groups to perform opposite actions. For example, the extensor muscle group of the foreleg extends the foot during protraction, while the flexor muscle group of the foreleg flexes the same foot during the retraction. It is this type of interplay that produces the well-balanced, beautiful motion we love to see in dogs.

    Protraction of the Foreleg
    Muscles involved in the concentric contraction that initiates the forward motion of the forelegs are as follows:
    1. The brachiocephalicus muscle
    2. The omotransversarius muscle
    3. The supraspinatas muscle
    4. The subscapularis muscle
    5. The coracobrachialis muscle
    6. The biceps brachii muscle
    7. The extensor carpi radialis muscle
    8. The common digital extensor muscle

     

    During protraction, the brachiocephalicus muscle pulls the shoulder joint up; initiating forward movement of the foreleg. At the same time the omotransversarius muscle pulls the ventral scapula forward while the serratus ventralis thoracis muscle contracts to assist rotation back and downward at the top of the scapula. The supraspinatus muscle the subscapularis muscle, the coracobrachialis, and the biceps brachii muscle extend the shoulder joint. The biceps brachii in the mastoid muscles cause flexion of the leg at the elbow. Then the extensor carpi radialis muscle and the common digital extensor muscle extend the paw as it comes to the ground. Also, other muscles such as the infraspinatus muscles, the thoracic part of the trapezius muscle, the deltoideus muscle and all of the pectoral muscles act as stabilizers in the protraction of the foreleg. During the protraction movement all the muscles involved in the retraction of the foreleg are you elongated and throughout their eccentric contraction, ensuring stability and smoothness to the movement.

    Retraction of the Foreleg
    The muscles involved in the concentric contraction that initiates the backward motion of the forelegs are as follows:
    1. The triceps muscle.
    2. The latissimus dorsi muscle.
    3. The flexor muscles.
    4. The rhomboideus muscle.
    5. The cervical trapezius muscle.
    6. The deep pectoral muscle.


    When the leg is fully protracted, the latissimus dorsi muscle and the triceps muscle are the main muscles responsible for bringing the leg backward. The deep pectoral muscle pulls backwards and towards the center of the dog; contributing to the leg retraction movement and helping prevent the leg for moving sideways. The play between the cervical and thoracic part of the serratus ventralis muscle allows the scapula to move up and forward. The rhomboideus muscle and the cervical part of the trapezius muscle provide extra pull on top of the scapula initiating the retraction movement. The rhomboideus also stabilizes the scapula during this movement. The flexor muscles in the foreleg provide extra push to lift the dog up and forward as the paw leaves the ground for the next stride. Also, other muscles such as the supraspinatus, the infraspinatus, and the deltoideus act as stabilizers to assist the retraction of the foreleg.
    All of the muscles involved in the protraction of the foreleg are elongated during the retraction movement and throughout their eccentric contraction, ensuring stability and smoothness of action.


    Abduction of the Foreleg
    The muscles responsible for the concentric contraction in the abduction of the foreleg are as follows:
    1. The supraspinatus and infraspinatus muscles.
    2. The deltoideus muscle.
    3. The rhomboideus muscle.
    4. The trapezius muscle.
    The elongated muscles involved in the abduction of the forelimb are as follows:
    1. The deep pectoral muscle.
    2. The superficial pectoral muscle.
    These muscles attach along the thoracic spine and the scapula and the bones of the foreleg. Their interplay induces the abduction movement.

     


    The deltoideus, the supraspinatus, and the infraspinatus muscles on the humerus bone laterally, bringing the leg to the outside. The trapezius and rhomboideus muscle assist this movement by pulling on the scapula up towards the top of the shoulder. The pectoral muscle group, in their eccentric contraction, contributes to the stability and smoothness of the movement.

    Adduction of the Foreleg
    The muscles responsible for the concentric contraction in the adduction of the foreleg are as follows:
    1. The deep pectoral muscle.
    2. The superficial pectoral muscle.
    The elongated muscles involved in the adduction of the foreleg are as follows:
    1. The supraspinatus and infraspinatus muscles.
    2. The deltoideus muscle.
    3. The rhomboideus muscle.
    4. The trapezius muscle.
    These agonist muscles are attached on the sternum and along the medial aspect of the humerus bone of the foreleg.
    The pectoral muscle group is principally responsible for this motion by pulling the leg medially (inward). The antagonist muscles, by their eccentric contraction, contribute to the stability and smoothness of action.



    Protraction of the Hindleg
    The muscles involved in the concentric contraction of the forward motion of the hind leg are as follows:
    1. The iliopsoas muscle
    2. The tensor fascial latae muscle
    3. The rectus femoris muscle
    4. The sartorius muscle
    5. The biceps femoris muscle
    6. The gastrocnemius muscle
    7. The extensor muscles

    The iliopsoas muscle runs deep from inside the pelvis to attach onto the inside aspect of the femur, below the femoral head. The iliopsoas muscle initiates the protraction movement by pulling the femur bone up and forward. This action flexes up the hip joint, the stifle joint and the hock joint. The sartorius muscle assists the iliopsoas muscle by pulling the stifle up and forward. The biceps femoris muscle and the rectus muscle also assists this action by pulling on the stifle joint and the tibia bone, causing the stifle to flex. Also, the contraction of the gastrocnemius muscles allows the flexing of the stifle. The extensor muscles of the hind leg flex the hock joint and extend the paw. All of the muscles involved in the retraction of the hind leg are elongated during the protraction movement, while their eccentric contraction ensures stability and smoothness.


    Retraction of the Hindleg
    The muscles involved in the concentric contraction of the backward motion of the hind leg are as follows:
    1. The gluteus muscles, especially the middle gluteal
    2. The hamstring group (semimembraneous, semitendinosus, biceps femoris muscles)
    4. The gastrocnemius muscle
    4. The deep flexor muscle
    The large middle gluteal muscle initiates the retraction movement. The hamstring muscle group is responsible for most of the power of the retraction. The gastrocnemius and the deep flexor muscles assist the flexion of the paw. The quadriceps femoris muscle assists in the extension of the hind leg at the end of the retraction movement. The adductor muscles facilitate this motion by gently pulling the leg medially. All of the muscles involved in the protraction of the hind leg are elongated during the retraction movement, while their eccentric contraction ensures stability and smoothness of action.



    Abduction of the Hindleg
    The muscles responsible for the concentric contraction in the abduction of the hind leg are as follows:
    1. The middle gluteal muscle.
    2. The superficial gluteal muscle
    3. The tensor fascia latae
    4. The biceps femoris muscle
    5. The quadriceps femoris muscle
    The elongated muscles involved during the abduction of the hind leg are as follows:
    1. The adductor muscle
    2. The gracilis muscle
    3. The iliopsoas muscle
    These muscles attach along the bones of the hind leg and their interplay causes the abduction movement. The tensor fascia latae muscle pulls the stifle laterally (outward). The movement is maintained by the action of the gluteus muscles, the biceps femoris, the quadriceps femoris muscle all pulling on the femur bone laterally. The antagonist muscles, by their eccentric contraction, contribute to the smoothness of action.



    Adduction of the Hindleg
    The muscles responsible for the concentric contraction in the adduction of the hind leg are as follows:
    1. The adductor muscles
    2. The gracilis muscle
    3. The iliopsoas muscle
    The antagonist muscles involved in the adduction of the hind leg are as follows:
    1. The gluteal muscles
    2. The biceps femoris muscle
    3. The quadriceps femoris muscle
    4. The tensor fascia latae muscle
    These muscles attach along he bones of the hind leg. Their interplay causes the adduction movement. The adductor muscles and the gracilis muscle are mainly responsible for this action by pulling the hind leg medially. The iliopsoas muscle assists this action. The antagonist muscles, by their eccentric contraction, contribute to the stability and smoothness of the movement.

     

     

    The Vertebral Column
    In addition to protecting the spinal cord, the vertebral column provides a frame-like structure made up of strong bones and very thick ligaments. The vertebral column’s role is to bridge the anterior and posterior limbs, to offer solid anchoring for the strong muscle groups, and to protect the spinal cord.
    Extension of the Vertebral Column
    The antagonist muscles responsible for the extension of the column are located above the spinal column. This extensor muscle group is made of:
    1. The spinalis dorsi muscles
    2. The logissimus dorsi muscles
    3. The iliocostalis dorsi muscles


    Flexion of the Vertebral Column
    All of the muscles below the spinal column are known as the column’s flexors. Not only do the abdominal muscles play an important role as flexors of the spine, but so do the muscle groups involved in attaching the limbs to the spine. To some degree, the intercostal muscles assist in the flexion of the spine as well. The muscles associated with protraction, retraction, abduction and adduction of the limbs also have a second function, that of supporting the backbone.

     

    Lateral Flexion of the Vertebral Column
    Lateral flexion or bending is not caused by any specific muscle. In fact, such bending is the result of a unilateral (only on one side) concentric contraction of either the flexor or extensor muscles of the spine previously mentioned. In this movement, the intervertebral muscles play a significant role. Running from one vertebrae to the next, the intervertebral muscles are tiny muscles along each side of the vertebral column. The large oblique muscles of the abdominal group are also important in producing lateral movement.


    The Rib Cage
    The pectoral muscles and the serratus ventralis muscles play an essential role in supporting and stabilizing the rib cage, or chest, in relation to the spine. The abdominal muscles assist lateral bending as well as support of the rib cage. The intercostal muscles are responsible for the actual movement of the ribs. The diaphragm muscle is responsible for breathing.

     

     

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