Muscle of the Month: Biceps Brachii
October's Muscle of the Month is the Biceps Brachii, the muscle which works in an antagonistic pair with the Triceps Brachii (July's muscle). This means that within the pair, as one muscle contracts, the other relaxes - when the Triceps contracts the Biceps relaxes. Continue reading to find out more.
The Biceps Brachii is located in the forelimb of the dog on the upper or proximal part of the limb. The muscle is biarticular which means it crosses two joints - the shoulder and the elbow.
The muscle has a single head, different to human anatomy where it has two heads, and it has a long spindle shaped structure. The fibres of the muscle run in a double pennate structure, meaning they run diagonally from either side of the tendon. This allows a higher force to be generated by the muscle, but range of motion is reduced.
The muscle's origin, where it begins, is the supraglenoid tubercle, which is a small rounded prominence of bone on the scapula (shoulder blade). From here the muscle crosses the shoulder joint and passes down the inside of the limb. The muscle splits and attaches to two insertion points - the radial tuberosity and the ulna tuberosity - a tuberosity is a rounded prominence on a bone. This point of insertion is at the elbow joint. The biceps brachii muscle is deep, mostly covered by the pectoral muscles, but the point where the muscle starts and ends can be felt.
What does it do?
Due to its location and structure, the main function of the biceps brachii is to stabilise the shoulder joint at the cranial border (side closest to the head). This function comes into play when the dog is standing, and also during movement in the stance phase - the part of movement when the forelimb is in contact with the ground.
The muscle also functions to flex the elbow joint, this happens as the stance phase finishes and the swing phase begins - the part of movement when the forelimb is off of the ground. The biceps brachii contracts and the elbow is brought into slight flexion to lift the limb off of the ground before it moves forward in walk/trot etc.
The final function of the muscle is to assist in passive extension of the shoulder joint, but this is not a key role because other muscles contribute more to this movement.
Can the Biceps Brachii become injured?
The muscle can be strained, overused or under used and weak, but the most common injuries to the muscle involve the tendon, which is the soft tissue structure that attaches the muscle to the bone.
The biceps brachii tendon can become inflamed following an acute injury, this is known as Tendinitis. Another condition that occurs in the tendon of the muscle is Tendinopathy. This is when collagen in the tendon breaks down. This happens due to repetitive injury, which is more often seen in agility and working dogs, because of the repetitive nature of the sport or work.
It has been found that biceps injuries are linked to the lack of blood supply to the origin of the muscle. Poor blood supply predisposes the tendon to injury, and also impairs healing resulting in scar tissue developing. This means that the tendon and muscle will not function as well as it used to.
When injury occurs to the biceps brachii the dog may show a mild, intermittent limp. On assessment, the area will be sore to touch, and stretching the muscle will also cause pain.
Treatment for biceps brachii and tendon injury will vary according to the severity. In some cases, rest and a rehabilitation programme from a physiotherapist will be sufficient. This process would start with icing of the area to reduce inflammation and restricted exercise/rest to also reduce inflammation and allow healing to take place. Massage, range of motion exercises, and stretching would all be used to optimise function of the muscle and tendon, keeping them flexible and reducing scar tissue formation.
Electrotherapy treatment may also be used to optimise healing of the tissue, and exercises will be added to strengthen the muscle and surrounding structures to prevent reinjury.
If the injury is more severe, alternative options may be required, such as regenerative medicine, which supplies everything that is needed for the tissue to heal well. In some cases surgery will be chosen to resolve the problem - release and reattachment of the tendon, or cutting of the tendon to remove the repetitive trauma. Reduced activity as well as physiotherapy will be needed in all cases to allow for the best recovery.
For more information please get in touch, see you for the next 'Muscle of the Month'.