Muscles control every aspect of movement
both internal and external. They form the largest tissue mass in
the horse’s body. There are various types of muscles performing a wide variety
of tasks all working in a similar way. Electrical impulses instruct the fibres
to contract and shorten then relax and lengthen. There are 3 types of muscle.
Smooth and cardiac, which function automatically as a result of voluntary or
autonomic activity within the brain and skeletal, which under voluntary or
conscious control, co-ordinate and create movement.
This is involuntary muscle which functions automatically. It surrounds and is found in all internal tissues and organs. Smooth muscle responds to stimuli from the autonomic nervous system. It is responsible for pushing food through the digestive system and the physical control of the bladder and bowel. It is also found in the vascular and reproductive systems.
This highly specialised, strong, thick and striated muscle is fatigue resistant. Beating around 100,000 times a day throughout the horses lifetime it co-ordinates the propulsion of blood in and out of the heart.
There are over 700 different skeletal muscles in the horse. The central Nervous System sends a signal to the muscles via nerves which then convert chemical energy into movement and the muscles, which are highly elastic and have strong contractile powers, react accordingly. The function of skeletal muscle is to:
• support the skeleton and create movement
• maintain joint stability and posture
• control range of movement
• protect the skeleton and internal organs from trauma
• contribute to thermoregulation by shivering
The Deep Muscles
The muscles attach to the bone via
the periosteum at the point of origin, which is nearest the body centre and the
point of insertion which is furthest away.
The function of the deep muscle is posture and stability. They:
- attach directly to the bone
- are located close to the joints
- often have a number of points of origin and insertion
- are often responsible for supporting individual joints. For example, the deep gluteal muscle only affects the hip joint
- have a high number of nerve endings which makes them more sensitive to postural alignment
The superficial muscles are located between the deep muscles and the skin. Although they vary in size and shape they are generally classified as movement muscles. They are either:
- bulky, such as the superficial gluteal muscles, around 25cm thick in a 16 hand horse. The triceps muscles, around 20 cm thick or the masseter muscle that moves the jaw
- or they are sheet like, such as the external abdominal oblique which span the entire abdomen and contributes to rib movement, bend and protraction of the hind limb
Superficial muscles in the hind quarters are large and powerful. Those running down the back of the hind legs extend the hip, stifle and hock joints and push the horse forwards over the planted hind limb. The superficial muscles between the front legs support the thorax and attach the forelimbs to the rest of the body whilst those running down the front of the forelimbs bring the limb forwards in protraction.
Muscles that have a tendency to become tight and sore require regular stretching and muscles that have a tendency to be ineffective, slow to support, long or weak benefit from regular strengthening exercises. Knowing which muscles need to be strengthened and which needs to be stretched comes from an understanding of the anatomy and bio-mechanics of the musculoskeletal system, movement and experience.
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