Equine Massage: A Practical Guide (30 page)

Eccentric contraction:
This takes place when a contracted antagonist releases its contracted state slowly to allow for better muscle control and to permit movement to be slowed down at will. This action contributes to the avoidance of jerky movements, making for elegance and suppleness in the horse’s performance. Eccentric contraction also acts as a shock absorber, a very important attribute during landing or any other abrupt movement.

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Motion

A horse’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.

To understand how a horse moves, we need to be aware of the interplay between the bones, joints, ligaments, tendons, and muscle groups that make the movements possible. Muscles are always arranged in opposing groups performing opposite actions; for example, the extensor muscle group of the foreleg extends the hoof during protraction, whereas the flexor muscle group of the foreleg flexes the same hoof during retraction. It is this type of interplay that produces the well-balanced, beautiful motion we love to see in horses.

Kinesiology of the Foreleg

Protraction

The muscles involved in concentric contraction (which initiates the forward motion of the foreleg) are (see figure 7.1):

7.1 Foreleg Protraction

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1. The brachiocephalic muscle

2. The cranial superficial pectoral muscle

3. The biceps brachii muscle

5. The thoracic part of the serrate muscle

During protraction, the brachiocephalic muscle (point 1; figure 7.1) pulls the shoulder joint up, initiating forward movement of the foreleg. At the same time, the thoracic aspect of the serrate muscle (point 5; figure 7.1) contracts to assist the rotation of the top of the scapula.The biceps brachii muscle (point 3; figure 7.1) causes flexion of the leg at the elbow.Then the extensor carpi radialis muscle (point 4; figure 7.1) extends the foreleg as the foot comes to the ground. In addition, the supraspinatus muscle, the thoracic part of the trapezius muscle, and the pectoral muscles (point 2; figure 7.1) assist the protraction of the foreleg.

All the muscles involved in the retraction of the foreleg are elongated during the protraction movement and through their eccentric contraction ensure stability and smoothness of action.

Retraction

The muscles involved in concentric contraction (which initiates the backward motion of the forelegs) are (see figure 7.2): 1. The triceps muscle

2. The latissimus dorsi muscle

4. The cervical part of the serrate muscle

6. The cervical part of the trapezius muscle

When the leg is fully protracted, the latissimus dorsi muscle and the triceps muscle (points 2 and 1 respectively; figure 7.2) are the main muscles responsible for bringing the leg backward.The caudal deep pectoral muscles (point 7; figure 7.2) pull backward and toward the center of the horse, contributing to the leg retraction movement and helping prevent the leg from moving sideways.

The play between the cervical and the thoracic part of the serrate muscle (point 4; figure 7.2) allows the scapula to move up and forward.The rhomboid muscle and the cervical part of the trapezius muscle (points 5 and 6; figure 7.2) provide extra pull on the top of the scapula. The deep flexor muscles (point 3; figure 7.2) provide extra pull to lift the horse up and forward as the hoof leaves the ground for the next stride.

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7.2 Foreleg Retraction

All the muscles involved in the protraction of the foreleg are elongated during the retraction movement and through their eccentric contraction ensure stability and smoothness of action.

Abduction

The muscles responsible for the concentric contraction in the abduction of the forelegs are (see figure 7.3): 1. The supraspinatus and infraspinatus muscle

2. The deltoid muscle

3. The rhomboid muscle

The elongated muscles in the abduction of the forelimb are: 5. The cranial superficial pectoral muscle

6. The caudal superficial pectoral muscle

7. The caudal deep pectoral muscle

These muscles attach along the scapula and the bones of the foreleg. Their interplay induces the abduction movement. The

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7.3 Foreleg Abduction

deltoid, supraspinatus, and infraspinatus muscles (points 1 and 2; figure 7.3) pull the point of the shoulder laterally, bringing the leg to the outside.The trapezius and rhomboid muscles (points 3 and 4; figure 7.3) assist this movement by pulling on the scapula. The pectoral muscle group (points 5, 6, and 7; figure 7.3) and the biceps brachii, in their eccentric contraction, contribute to stability and smoothness of movement.

Adduction

The muscles responsible for adduction of the forelimb are (see figure 7.4):

1. The cranial superficial pectoral muscle

2. The cranial deep pectoral muscle

3. The caudal superficial pectoral muscle

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The elongated muscles in the adduction of the forelegs are: 5. The subscapularis muscle

6. The supraspinatus and infraspinatus muscle

7. The deltoid muscle

8. The rhomboid muscle

These muscles attach to the scapula and along the bones of the foreleg; their interplay induces the adduction movement.The pectoral muscle group (points 1, 2, 3, and 4; figure 7.4) principally causes this motion by pulling the leg medially (inward). The antagonist muscles (points 5, 6, 7, 8 and 9; figure 7.4), by their eccentric contraction, contribute to stability and smoothness of action.

7.4 Foreleg Adduction

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Kinesiology of the Hind Leg

Protraction

The muscles involved in the concentric contraction (which initiates forward motion of the hind leg) are (see figure 7.5): 1. The iliopsoas muscle

3. The quadriceps group of muscles (lateral vastus) 4. The biceps femoris muscle

5. The gastrocnemius muscle

The iliopsoas muscle, made of the iliacus and psoas muscles (point 1 and 2; figure 7.5) initiates the movement by pulling the femur up and forward. This action flexes the hip joint, the stifle joint, and the hock joint. The biceps femoris muscle and the lateral vastus muscle (points 4 and 3 respectively; figure 7.5) assist this action by pulling on the stifle joint and the tibia. The gastrocnemius muscle and the digital extensor muscle (points 5 and 6; figure 7.5) assist in the flexion of the fetlock joint.

7.5 Hind Leg Protraction

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All the muscles involved in the retraction of the hind leg are elongated during the protraction movement and through their eccentric contraction ensure stability and smoothness of action.

Retraction

The muscles involved in the concentric contraction (which initiates backward motion of the hind leg) are (see figure 7.6): 1. The gluteus muscles (especially the medial gluteus) 2. The hamstring group of muscles (the semitendinosus, the semimembranosus, and the biceps femoris)

3. The lateral vastus muscle

4. The biceps femoris muscle

5. The gastrocnemius muscle

The large gluteus medius muscle (point 1; figure 7.6) is attached to the back of the femur; it initiates the retraction movement.The hamstring muscle group (point 2; figure 7.6) is responsible for most of the power of the retraction; the adductor muscles assist in

7.6 Hind Leg Retraction