Key Muscles of the Equine Respiratory System & Their Impact on Performance

Your horse’s performance is intimately tied to his ability to breathe freely and deeply. Breathing involves several key muscles that help facilitate the process of inhalation and exhalation. These muscles work together to expand and contract the lungs, allowing for the exchange of oxygen and carbon dioxide. In this article, we’ll discuss the muscles behind respiration and how it affects your horse’s performance:

1. Diaphragm: The diaphragm is the primary muscle responsible for initiating inhalation. When it contracts, it moves downward, expanding the chest cavity and creating a vacuum that draws air into the lungs.

Exhalation, at least at rest, is a passive process. Once the diaphragm relaxes and returns to its dome-shaped resting position, it reduces the space in the chest cavity. This reduction in space increases the pressure inside the lungs, causing air to be expelled passively through the trachea and out of the nostrils. The diaphragm doesn’t actively contract to push air out as it does in humans.

Equine respiratory system

During exercise or periods of heavy breathing, horses rely on additional muscles in the neck, chest, and nose for breathing support contribute to efficient inhalation.

2. External Intercostal Muscles: These muscles are located between the ribs and assist in expanding the ribcage during inhalation. They elevate the ribs, further increasing the thoracic cavity’s volume.

3. Internal Intercostal Muscles: These muscles are deeper and assist in exhalation by depressing the ribs, reducing the thoracic cavity’s volume during forced exhalation.

4. Serratus Dorsalis: The Serratus Dorsalis is divided into two parts: the serratus dorsalis cranialis and serratus dorsalis caudalis. These muscles assist in lifting and stabilizing the ribs during both inhalation and exhalation in horses.

Serratus dorsalis caudalis

5. Serratus Ventralis: The Serratus Ventralis is divided into 2 regions, cervical and thoracic. One of its many roles is to aid inspiration.

Serratus Ventralis

6. Dilator Nares Muscle: This muscle, also known as the dilator muscle of the nostrils, runs horizontally across the nostrils. When it contracts, it widens or dilates the nostrils, allowing for increased airflow. This is especially important during strenuous exercise when the horse requires more oxygen.

Dilator Nares

7. Accessory Muscles: Smaller muscles in the neck and chest may also contribute to your horse’s breathing, particularly during strenuous activities or heavy breathing. These muscles provide additional support and facilitate the expansion of the thoracic cavity when the horse needs to take in more air during demanding activities. These include:

a. Scalene Muscles: The scalene muscles are found in the neck and consist of three separate muscles: the anterior, middle, and posterior scalene muscles. These muscles play a role in elevating the first two ribs and aiding in deep inhalation. They are involved in expanding the thoracic cavity to accommodate increased airflow.

b. Sternohyoid and Sternothyroid Muscles: These muscles are located in the neck region and are involved in stabilizing the larynx and trachea during breathing. They assist in maintaining airway integrity, which is crucial for efficient airflow.

c. Pectoral Muscles: The pectoral muscles are located in the chest region and have a broader role in controlling the movement of the front legs. During heavy exercise, these muscles can indirectly influence the chest’s expansion and contribute to deep breaths.

d. Serratus Ventralis: This muscle helps to support and control the movement of the scapula (shoulder blade). While not primarily a respiratory muscle, it indirectly plays a role in chest movement during strenuous activities.

e. Scalenus Cervicis: This muscle is part of the scalene muscle group and assists in elevating the cervical (neck) vertebrae, which can help create more space for airflow during deep inhalation.

8. Abdominal Muscles: When a horse breathes heavily, either due to strenuous exercise, a stressful experience or a condition like COPD that restricts airflow, he depends on his abdominal muscles to forcefully contract and push the diaphragm upward. This action aids in expelling air from the lungs, enhancing respiratory efficiency. These abdominal contractions can be part of the canter or gallop stride or can occur as a separate action.

Intercostals and abdominals

These muscles work in a coordinated manner to ensure the horse’s respiratory system functions efficiently, allowing them to meet their oxygen requirements during various activities. If any of these muscles are constricted by tension, restricted fascia, pain or poor posture, oxygen intake will be reduced and your horse’s performance will suffer. Massage with myofascial release addresses the whole horse to balance muscular tension, mobilize fascia, restore correct mobility and improve posture, breathing and performance.

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