Biceps Brachii Muscle

Biceps Brachii Muscle

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Biceps Brachii is a deeply placed muscle covered by the Superficial Pectorals.

As an intrinsic muscle it's found in the cranial brachial region.

Humans

In humans, the Biceps Brachii is a fusiform shaped muscle with its muscle fibres arranged in a parallel orientation within the muscle belly, converging to a tendon. It lies just under the skin and has 2 heads.

Dogs

However, the canine Biceps Brachii is very different, as it lies deep and is covered by other muscles and has only 1 head. It's a spindle shape muscle and is double pennate.

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Muscle architecture, shape and muscle fibre orientation are design features to facilitate specific muscle roles and actions. Know your species anatomy!

The significant difference in muscle shape and fibre alignment across the two species (human and dog) indicates the need for specific canine treatment techniques, as the dog's biomechanical design is totally different to the human model. Human treatments are for humans!

Proximal Attachment

The muscles origin is the supraglenoid tubercle of the scapular and the long tendon of origin is held in the intertubercular groove by the transverse humeral retinaculum.

The retinaculum is a band of thickened deep fascia and its key function is to stabilise the Biceps Brachii tendon.

The greater tubercle of the humerus is a useful bony landmark for considered therapeutic palpation, to locate the Bicep Brachii tendon of origin. The lesser tubercle is very deep and medially placed and a systematic and mindful palpation method is always best for the dog.
The greater tubercle of the humerus is a useful bony landmark for considered therapeutic palpation, to locate the Bicep Brachii tendon of origin. The lesser tubercle is very deep and medially placed and a systematic and mindful palpation method is always best for the dog.
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Clinical Tip: For accurate and relevant information, it's very useful to palpate the dog in different postures. The dog's natural fascial tension changes in the different postures which a dog uses throughout their day. Evidence shows that muscle tension also alters in response to the emotional status of the dog during the palpation experience.

Distal Attachment

The Biceps Brachii tendon of insertion splits into 2 parts, with the larger part inserting onto the ulna tuberosity (proximal ulna) and the smaller part onto the radial tuberosity (proximal radius).

Biceps Brachii = red
Biceps Brachii = red
Brachialis muscle = blue
Brachialis muscle = blue
Muscles that pass over 2 joints will have an action at both joints and are much more prone to injury compared to muscles that pass over one joint.

The canine Biceps Brachii design is linked directly to its incredibly important role in fixation of the shoulder joint in standing balance.

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The mechanical arrangement of Biceps Brachii is further supported by the evidence of a high percentage of Type I fatigue resistant muscle fibres. This is an ideal muscle design feature to provide postural maintenance.

Innervation of Biceps Brachii

Biceps Brachii is innervated by the musculocutaneous nerve, which is part of the brachial plexus.

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Clinical Tip: The shoulder joint capsule continues under the tendon of origin as a cushion, along the intertubercular groove. If you palpate swelling cranially between the greater and lesser tubercle of the humerus, this indicates a shoulder joint effusion. Always use Therapeutic Handling and Therapeutic Touch in your assessment as this is a deep palpation technique. Work with your dog and not on it!

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