Muscle Biomechanics: Biceps Brachii Muscle

This is the first post of a long series of posts that will reveal the lesser-known functions of our muscles.

In fact, almost every muscle in our musculoskeletal system performs more than one movement related to one or two joints.

Specifically, this post will analyze the functions of the Biceps Brachii which is the most important muscle of our arm.

The Biceps Brachii is so-called to distinguish it from the brother Biceps Femoris as the adjectives Brachii and Femoris indicate their allocation and connection with the Humerus (arm) and Femur (leg) bone respectively.

Anatomy of the Biceps Brachii Muscle

The Biceps Brachii is a bi-articular muscle as it is connected with two joints:

  1. Hulnohumeral Joint ( Elbow Joint ).
  2. Glenohumeral Joint ( Shoulder Joint ).

The biceps femoris consists of two muscle strands (spindles):

  1. Long Head
  2. Short Head

The long head originates in the supraglenoid tuberculum of the scapula.

The short head originates at the apex of the coracoid process.

Both the Long and short heads joint to form a common muscle belly and they attach through a common tendon into the tuberosity of the radius ( medial aspects of the radius bone ).

The Biceps Brachii has innervated by the Musculocutaneous nerve ( C5, C6, C7 ).

Biceps Brachii Anatomy
Biceps Brachii's Origins and insertion

Actions of the Biceps Brachii Muscle

Since the Biceps Brachii has its origin and insertion in three different points It crosses the elbow and the shoulder joints, and it can make more movements of both the arm and the forearm.

The main actions of the Biceps Brachii are:

  1. Flexion of the forearm.
  2. Supination of the forearm.
  3. Shoulder Flexion on the first 30° ( Dynamic Stability to help the primary shoulder’s muscles flexors: Deltoid and Pectoralis Major Muscles ).

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Biceps Brachii’s injuries

There are different points of the biceps brachii muscles’ structure that can be affected from muscle or tendon rupture. These different ruptures point can lead to partial or total loss of function.

We can have 3 main tendon ruptures:

  1. Long Head rupture ( partially loss of function as there is still the short head connection ).
  2. Short Head rupture ( partially loss of function as there is still the long head connection ).
  3. Rupture of the common tendon into the tuberosity of the radius ( complete loss of function as there is no more insertion point ).

Muscle tears or strain generally occur at the shoulder end, in the proximity of the tendons. Generally, they don’t require surgical treatment.

The most common symptom of biceps tendon rupture is pain in the upper or lower arm, which can lead to bruising, muscle spasms, or loss of mobility and strength.

The image below shows a long head’s rupture. The bruising comes from damage following rupture of the tendon. It doesn’t show up here really well, but there is commonly a “popeye” effect of the biceps, bulging abruptly on the middle portion of the humerus.

Rupture of the long head of the Biceps Brachii
Biceps Brachii's Long Head Rupture

Biceps Bachii Injury Treatment

Tears of the biceps tendon at the elbow are uncommon and most often result from lifting heavy weights. This rupture requests surgical treatment to reattach the tendon to the bone and regain full arm strength and function.

Between tears at the biceps tendons at the shoulder is more common that one of the Long Head.

For most people, surgical treatment of the Long Head is not necessary as mild arm weakness or arm deformity does not typically bother most patients.

However, those who develop cramping of the muscle or pain, or who require complete recoveries of the strength, such as athletes or manual laborers, may benefit from the surgery.

Muscle strain and tears of the biceps brachii can be treated with a sports therapy, such as a Sports Massage to ease the muscle stiffness and trigger points that have led to the muscle strain or tear. 

When treating a biceps injury it is important to treat all the other muscles that have the same actions, such as Coracobrachialis MuscleBrachialis Muscle, Deltoid Musclesand Pectoralis Major Muscle. In fact, they could be the causes of the biceps’ excessive strain both because of their weakness or stiffness.

Be aware, that if you get a Biceps Brachii injury, seek the help of a specialized Sports Therapist or of your doctor and avoid self-treatment.

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