Muscle of the Month: Superficial Pectorals
Starting 2021 with January's Muscle of the Month, the Superficial Pectorals which are made up of the descending pectorals and the transverse pectorals. An important muscle in the dog for both stability and movement - read on to find out more.
The Superficial Pectorals are located between the forelimbs, in the chest area, with a left and right portion coming from the central point of the chest. The descending pectorals are a smaller narrow band of muscle, with the transverse pectorals lying directly underneath, wider in shape. The muscle is described as superficial because it is close to the skin and be felt easily.
The muscle originates or starts from the manubrium, which is the thickest part of the sternum or chest bone, on the cranial part, which means the part of the bone closest to the head. From this point the muscle fans out to the each forelimb, inserting or ending on the humerus bone, between the shoulder and elbow joint. As you can see from the diagram this muscle therefore makes an attachment between the body of the dog and the limbs.
What does it do?
The superficial pectorals have multiple functions - firstly in movement, the muscle protracts the forelimb, bringing it forward in front of the body, and retracts the forelimb, bringing it backward. Protraction and retraction are key features of every gait that the muscle helps to create.
Due to its position, the muscle also creates adduction movement of the limb, which means moving the limb inwards, towards the middle of the body. An example of this would be when your dog is turning, they bring their limbs inward and across their body to rotate. For this reason the superficial pectorals are an important muscle for many sporting dogs e.g. weave poles in agility or turning off the box in flyball.
The final role of the superficial pectorals is to give stability to the forelimb. Humans have a collar bone which attaches the forelimbs to the body, dogs do not have a collar bone. The pectorals have a role in attachment of the limbs to the body, along with other muscles of the shoulder.
Can the Superficial Pectorals become injured?
This muscle may not be an obvious site of injury, but due to its function in movement, it can be strained or torn. Sudden twists or turns will put excess force through the muscle and potentially cause damage. An appropriate warm up and cool down will help to reduce the risk of injury to the muscle - ask a physio for advice on how to do this.
In some dog's that have weaker hindlimbs or an injury to the hindlimbs, weight can be shifted forward, causing an increased load on the pectorals. This can lead to overdevelopment of the muscles, soreness in the muscle, and possibly tension. In the image below you can see a dog that is leaning forward, taking the weight off of his hindlimbs - his pectorals are very prominent and increased in size.
Certain breeds do naturally load more heavily on their forelimbs (bull breeds for example), and over time this can cause long term issues such as arthritis in the joints of the forelimbs. With these breeds it is important to ensure their hindlimbs and core are strong to prevent further weight shifting onto the front - a physio can prescribe exercises to help with strengthening.
If the pectoral muscles were strained this can be managed with rest, icing, and in more severe cases anti-inflammatory medication. Physiotherapists can then help with a programme for safe return to exercise, to avoid re-injury.
As a physiotherapist, I observe every dog I treat and would be able to see if your dog was loading their weight forward into their chest. I can then help to address this with; stretching to release tension, massage to relieve pain and tension, and exercises to strengthen the core and hindlimbs. By doing all of these things, your dog's posture should improve, taking the excess strain away from the pectorals.
For more information please contact me, see you next month to learn about another muscle!