When we talk about the arm muscles and the muscles that act on the elbow and shoulder joint, most people will go directly to the glamour muscle - the biceps brachii. This largely over-rated muscle is the doyen of masculinity and pose worthy instagram postings. For many men, it defines strength, it defines power and the dominion over other less endowed, 165lb beings. In the wild it would be akin to a lion’s roar or a wolfs shackles, a showy display of aggression, challenge and domination. It imbues egos, wards off worthy suitors to partners and is the go to muscle of choice when parading in front of the mirror post workout or the glassed in elevator. (come on fellas - we all know we do it).
The Biceps Brachii though is by far not the most important or valued member of the Brachii family and there are a couple of other Brachii muscles that by far are more important in flexion and shoulder alignment as well as power when lifting heavy loads. The predominant action associated with the arm muscles are elbow flexion along with supination and pronation of the forearm. In regards to elbow flexion, Biceps Brachii must give way to it’s more powerful brother the Brachialis, who lies deep to biceps brachii and generates up to 50% more power in the elbow flex.
The other main action is supination and pronation of the forearm against the humerus. This action is where Biceps Brachii has more claim rotating the arm from pronation to supination (which is why the palm faces inward on a bicep flex not outward). The other main Brachii brother is the Brachioradialis, which rotates the forearm against the humerus. It is involved in all three actions of flexion, supination and pronation but is most powerful when the forearm is in the midway position between supination/pronation. (this explains Hammer Curls). When the forearm is pronated Brachioradialis exerts more force in elbow flexion over Biceps Brachii who is more powerful in the supinated position. It also supports Biceps Brachii in moving between supination/pronation.
There is however a role for the upper arm muscles in flexion of the shoulder joint anteriorly and also in the stability of the glenohumeral joint in load bearing. Of the three upper arm muscles noted, the Biceps Brachii is the one muscle that does contribute to the action of shoulder flexion, adduction and abduction. Whilst Biceps Brachii isn’t the primary mover in these actions, it is a secondary contributor (synergist) and more importantly a stabliser in actions, so tension or shortening here is going to affect the shoulder movements. These factors bear an important understanding when it comes to rehabilitating shoulder issues and also in keeping shoulder alignment optimal.
Now shoulder movement and flexion is generated primarily by the Pectoralis Major, however the Biceps Brachii acts as a synergist of movement in shoulder flexion. It also plays this role in abduction and adduction of the glenohumeral joint with the deltoids being the primary mover in adbuction and Coracobrachialis/Teres Major/latissimus dorsi being the prime movers in adduction. The Long Head of the biceps that inserts on the scapula (supraglenoid tubercle) is more active and assists in abduction of the arm whilst the short head that orginates at the coracoid process of the scapula, is more active in adduction. Thus the Biceps Brachii is very much an influence in the movement of the shoulder in its most common movement patterns and thus any tension or shortening here can have an influence on the biomechanics and the recruitment of other muscles in shoulder movements.
Clinical trials have identified that shortness in the Biceps Brachii correlates to a rounded shoulder position. Due to the nature of the origin of the short head at the coracoid process, the short head is involved as a fixator of the shoulder in flexion, it can create a downward pull on the scapula and can anteriorly rotate the shoulder. Hence in shoulder rehabilitation and treatment, addressing the biceps can be of great benefit to ensuring structural integrity. It is not always the prime mover that is the cause of structural deformity.
So when it comes down to it, the Biceps Brachii is not the only glamour muscle of arm and shoulder movement. In training the biceps, it is best to focus on how best to train any muscle. In this way you need to address factors such as the joint movement, the angle that best utilizes the target muscle and the internal moment length (the length between a joint axis and the line of force acting on that joint). In this way it gets tricky as you have to target the muscle according the joint axis movement. In the case of working your elbow flexors, working with a straight arm is going to activate the prime mover of elbow flexion (brachialis).
Movements that combine elbow flexion WITH supination/pronation are going to target the Biceps Brachii and Brachioradlalis. In this way you can see why those targeting hypertrophy of select muscles will need to accent their training along those lines that best target the desired muscle. As opposed to those that want to work functionally and even more for issues such as straight arm strength more than bent arm strength, this is going to impact which exercises you target and what type of eccentric/concentric/Time under tension factors you include.
So - depending on who you are and what your goal is, the elbow flexion is not just a single muscle focus. For even the most basic of goals, if you want those guns to be big then you need to target more than just elbow flexion. Supination is every bit as important. And if size is your thing, you actually should be looking at targetting your triceps as they make up 2/3 of your arm size. But that’s another blog…