Posted on 20 Oct 2012 20:17
The brachialis muscle is located on the front part of the upper arm, nearest the elbow. Along with the biceps brachii and the brachioradialis, it is one of the primary flexors of the elbow. It gets its name from the Greek words brachialis and brachion, pertaining to the (upper) arm. It is important not to confuse these words with the Greek brachy which means "short." Although not as large as the biceps brachii, the brachialis is a relatively large and wide muscle and these two muscles, along with the coracobrachialis, make up the anterior (front) compartment of the upper arm. Unlike the biceps brachii, which attaches to the radius, the brachialis attaches to the ulna, making it suited for flexion of the elbow only, since it can only pull on the ulna and the ulna does not rotate. However, it provides strong elbow flexion in both supination and pronation.1,2
In fact, the brachialis has been called a "Workhorse Elbow Flexor" working intricately with the biceps brachii but doing much of the work that we usually attribute to the biceps. The biceps is large and superficial to the brachialis, which lies beneath it, so it is easily overlooked. Based on cross-sectional analysis of the major elbow flexors, the brachialis appears to provide 47% of the torque for elbow flexion while the biceps provides 34% and the brachioradialis contributes 19%. The muscle may also contribute to stabilization of the elbow joint.1,2 The image below illustrates the location of the brachialis relative to the biceps.
Biceps Superior to Brachialis on Anterior Arm
When the shoulder joint is fixed, as during a curling exercise, the brachialis moves the ulna, and thus forearm, toward the humerus. When the forearm is fixed, the muscle moves the humerus toward the forearm, as during pullups or chinups. If a heavy object were dropped into the outstretched palm, the brachialis would contract in an eccentric action to decelerate the lowering of the forearm, along with the biceps.2
The brachialis originates on the anterior part of the distal humerus, having a long and wide area of attachment, starting in the area where the deltoid inserts and ending closer to the elbow on the anterior humerus where the origin forms an inverted "V" shape, just above the elbow joint. The way the muscle is situated on the distal humerus, below the midpoint of the shaft, makes it partially envelop the bone on the anterior, lateral, and medial aspects so that around two-thirds of the bone's circumference is covered. The belly of the brachialis is relatively flat and becomes concave on the front and convex on the back as it extends towards its insertion at the ulna. The middle fibers run vertically, the medial fibers run obliquely from medial to lateral, and the lateral fibers run obliquely from lateral to medial. These portions become tendinous at different points before converging to insert on the anterior aspect of the base of the coronoid process of the ulna.
Brachialis Muscle with Its Relationship
to Deltoid Insertion and Biceps Tendon
There are several variation and anomalies possible, including the muscle being divided into two or more separate heads or bellies, with each head originating at a different point, anterior and posterior to the deltoid insertion. The distal insertion may becomes more variable in this case, with additional or different insertional sites including the radius or radius and ulna, and other variations.1
Brachialis Origin, Insertion, and Action
Origin: Distal half of anterior portion of humerus, covering a long and wide area starting near the deltoid insertion and ending close to the elbow on the distal humerus.
Insertion: Coronoid process of the ulna bone.
image by robswatski via flickr
Action: Strong flexion of the elbow, the only pure flexor of the joint. Many of the activities which use and work the biceps brachii also work the brachialis. The muscle can be somewhat preferentially isolated by pronating the forearm, which makes the biceps somewhat less effective. However, the interplay between the brachialis, biceps and brachioradialis during resisted elbow flexion is not nearly as predictable as most sources claim, being quite variable even in one individual on repeated subsequent efforts, making true and consistent isolation of any one elbow flexor unlikely.2,3,1
Synergists: The brachialis is synergistic with the biceps brachii as prime mover in elbow flexion. It is often claimed to be a secondary mover or assistant to the biceps but it is proper to call it a chief mover, along with the biceps, if not the main mover. Both muscles have large swing components and small stabilization components. They are assisted by weaker synergists of flexion including the brachioradialis, pronator teres, and the wrist and finger flexors flexor carpi ulnaris, flexor carpi radialis, and flexor digitorum sublimis, which have small swing components (the brachioradialis being the largest swing muscle of these) and strong stabilizing components so that these muscles mostly stabilize the elbow during flexion and extension while providing a little assistance to the brachialis and biceps brachii for elbow flexion. (See What is an Agonist, Antagonist, Stabilizer, Fixator or Neutralizer Muscle?) 4,2
Brachialis Trigger Point Causes and Symptoms
The brachialis can be overworked by anything that requires repeated and/or sustained bending of the elbow, especially under load. Carrying groceries, using handheld power tools for long periods, repeatedly picking up children, carrying a purse or bag hanging on the forearm, fingering a guitar or violin with the forearm supinated, etc. Sustained computer work or driving may also aggravate the muscle.2,5
When exercising with elbow flexion, such as with barbell or dumbbell curls or with chinups/pullups, "doing too much too soon" can overwork or strain the muscle. Avoid excessive use reverse curls, which are weighed curls with the hand pronated (palms facing down or almost down), so as not to over-burden the brachialis (although it is perfectly okay to do this moderately, just not exclusively).
Neither the biceps or brachialis is activated when the arm is carrying a load in a fully extended position, and gravity is pulling the load straight down, so strain to the muscle through carrying exercises or deadlifts is only likely if unintentional elbow flexion is done, or the forearm is suddenly and violently extended. Although the ruptures of the proximal or distal biceps tendon are somewhat common, rupture of a brachialis tendon is rare.1,2
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licensed under CC Attribution-Share Alike 2.1 Japan
Although most of the same activities that set up trigger points in the biceps brachii can also set up trigger points in the brachialis, the symptoms are quite different. Most of the referred pain from trigger points in the brachialis is in the volar part of the carpometacarpal joint of the thumb (opposite the palm at base of thumb) and also to the web of the thumb in that area. This pain may be felt at rest or also with use of the thumb. There may also be a diffuse tenderness in the thumb. Since the brachialis is capable of entrapping the superficial sensory branch of the radial nerve, there may be dysesthesia, tingling, and numbness in this area of the thumb. The pain and tenderness in the thumb, and the entrapment symptoms, may be caused by trigger points in different areas of the muscle.2,6
Oboe, clarinet, and sometimes saxophone players experience chronic thumb pain and numbness, usually on the right hand, which can easily be mistaken for a thumb problem, since the thumb is certainly used a lot as a buttress for fingering the instrument, while supporting the weight of the instrument. But the real problem may be that the brachialis has to stay contracted continuously while playing the instrument, and the symptoms in the thumb are caused by trigger points in the muscle.2,5
The trigger points that occur more distally (closer to the elbow) may refer some pain to the crook of the elbow. The trigger points that occur further up, closer to the deltoid insertion refer spillover pain mostly upwards toward the deltoid. This does not affect movement at the shoulder.2
Brachialis Trigger Point Self Treatment
The figure below shows the locations and referred pain patterns of brachialis TrP's. To avoid these or to avoid aggravating existing TrP's, try not to overwork the muscle, as described above. Also, when the elbow must be continually flexed as when working with tools or playing an instrument such as woodwind or guitar, put down the instrument at every opportunity and allow the arm to hang freely and relax, so as to rest the muscle and help return it to its resting length. Do not hold a purse on the forearm with the elbow bent, instead hold it in the fingers with the arm dangling or with the strap over the opposite shoulder. Remember that corrective actions and avoidance are really the same things, but for correction, you must be more diligent.2,5
Brachialis Trigger Points and Referred Pain Patterns
The brachialis can be stretched by supporting the back of the upper arm, as on the arm of a chair, with the arm stretched out in front of you and the palm turned up. Push down on the wrist to gently stretch the muscle. Do this several times a day.2
There may be a trigger point closer to the elbow and another a bit further away, but both are fairly close to the elbow. Remember, the muscle does not even stretch all the way to the shoulder joint. Although the brachialis lies under the biceps, it can be palpated and self-massaged by pushing aside the biceps. Using the fingers or knuckles, starting just above the crease of the elbow, push the biceps toward the body (medially) and massage the brachialis underneath against the humerus bone. To facilitate this, sit in a chair and lean forward so that you can rest you elbow on your thigh, to support the arm while massaging the muscle. Feel for trigger points starting at the elbow crease and working your way up. The trigger point that occurs in the upper position may be the one causing entrapment of the radial nerve, if you are experiencing entrapment symptoms. Expect associated trigger points in the biceps brachii, brachioradialis, and/or supinator teres.5
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This page created 20 Oct 2012 20:17
Last updated 23 Feb 2015 19:15