This week's muscle is the Ascending Pectoral (aka. deep or caudal pectoral). It is the third muscle in our four part pectoral series. Let's get to it!
L O C A T I O N:
It starts not only on the sternum (all the way to its caudal end), but also on the outside of the abdominal muscles and the cartilages of the fourth to ninth ribs. It goes forward inside the leg to the front of the humerus and attaches to its top end. The Ascending pectoral muscle is the largest muscle in the group, has a fan/triangular shape, and is the only muscle in the group that comes into contact with your girth.
F U N C T I O N:
Suspension of the trunk between the thoracic limbs, forelimb retraction, and stabilization of the glenohumeral joint. It also reinforces the action of the latissimus dorsi (supports the back, pulling body of the horse forward when the foreleg is placed on the ground and flexes the shoulder). It is really important in pulling the leg back relative to the body or moving the body forward relative to the leg, depending if there is weight on the leg or not. It also acts to pull the leg in towards the body.
S Y M P T O M S O F P A I N:
- Rapid jerking of the back upwards with a light to medium palpation
- Objection and struggle to perform a forelimb protraction stretch
- Shortening of stride; poor synchronicity
- Decreased stamina
-Shortening of cranial phase of step cycle
- Placement of the limb medially (towards the center) during the weight bearing phase of step cycle
But as you can see in the picture, regardless if the cinch lies close to the front leg or farther back, it will put pressure on this muscle. Too much pressure from the cinch, either because it is too tight or because is too narrow and therefore has poor distribution of pressure, will inhibit this muscle's activity in moving the horse forward. It may also cause decreased blood flow, damage and pain in this muscle, all of which will affect the horse's movement.
Tune in next week for the last muscle in this series, the Subclavius, and we'll try to wrap up the pectorals and "put it all together" in what they mean for your horse! See you next week!
Muscle Monday Posts!
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