The Biceps and Triceps Muscles: Forearm Movers
The muscles that move our forearms are essential for all the functional movements we do that require placing our hands in a position to grasp something. That includes activities like driving a car because, of course, we have to grasp the steering wheel. It also includes fine motor activities like writing and typing. Placing our hands in a particular position is the job of the shoulder and arm, but especially the job of the elbow and forearm. Two of the key muscles for moving the forearm are the biceps brachii and triceps brachii. In this article, we’ll look at these two muscles. Read on to learn where they attach, what they do, and how they relate to each other.
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The biceps and triceps relationship
While there are several muscles that cross the elbow joint to move the forearm, in this article, I focus on the biceps brachii and triceps brachii. That’s because, in addition to being key movers of the forearm, they are antagonists. That means that they are always acting in relation to each other.
As we look at the attachments and actions of muscles, it’s important to remember that no muscle works alone. When we apply kinesiology concepts to functional movement, we’re never seeing just one muscle. We’re seeing the relationship of tension and direction of all the muscles that surround and act on a particular joint. Keep that in mind as we look closer at the biceps brachii and triceps brachii.
Locations
Biceps brachii
The biceps brachii is located in the anterior compartment (front) of the arm along with brachialis and coracobrachialis. This muscle typically has two muscle bellies, called heads. The muscle name describes this. Bi means two, and cep means heads. However, there is some variation in the number of muscle bellies among the larger population. A very small percentage of people have more than two heads in the biceps muscle. The two heads of biceps are referred to as the long head and the short head.
Triceps brachii
The triceps brachii is in some ways the mirror image of the biceps brachii. It’s located in the posterior compartment (back) of the arm. As you might guess from the name, it typically has three muscle bellies, or heads. Tri means three, and as I said already, cep means head. As with the biceps brachii, there is some variation in that, however. A very small percentage of people have more than three heads in the triceps muscle. The three heads of triceps are called the long head, lateral head, and medial head.
Muscle attachments
Biceps brachii
The two heads of the biceps brachii both attach proximally to the scapula, but they attach to separate places. Farther down, they merge together into a single tendon at the distal end. Proximally, the long head of biceps attaches to the supraglenoid tubercle of the scapula. The short head attaches proximally to the coracoid process of the scapula. After the long head and short head merge into a single tendon, it attaches distally onto the radial tuberosity and merges into the fascia of the forearm.
Triceps brachii
Like the biceps brachii, each of the three triceps brachii heads attaches to a separate place at the proximal end. One head, the long head, attaches to a place on the scapula called the infraglenoid tubercle. The other two heads attach to the humerus (upper arm bone). The lateral head attaches proximally to the humerus, superior to (above) a depression in the bone called the radial groove. The medial head attaches proximally to the humerus, inferior to (below) the radial groove.
Although they originate proximally in three separate locations, the three heads of triceps brachii combine into a single tendon distally. It attaches to the olecranon process of the ulna (the smaller of the two forearm bones).
Muscle actions
Biceps brachii
Like most muscles, both the biceps and triceps do some primary actions as well as assist in some additional actions. The main action of the biceps is supination of the forearm. That’s the action that happens when we rotate to turn our forearm and hand palm up. Both heads of the muscle work together to do that action.
The two heads also work together to assist in flexing the forearm at the elbow and flexing the arm at the shoulder. The biceps is not the prime mover in either of these actions, but it assists other muscles to help create them. Because of the position of its proximal attachment on the scapula, the long head can also help stabilize the shoulder joint.
Triceps brachii
All three heads of triceps brachii work together to create its main action, which is extension of the forearm at the elbow. The long head, because of its proximal attachment to the scapula, can assist other muscles in extension and adduction of the arm at the shoulder joint. Like the long head of the biceps, it can also contribute to stabilizing the shoulder at the shoulder joint. The lateral head helps stabilize the elbow joint in extension when we want to add a supination or pronation movement, or do fine motor movements with our hands and fingers.
Biceps and triceps relationship
As we describe the individual movements and stabilization actions of the biceps and triceps, you can see that they are related. The biceps flexes the forearm at the elbow, and the triceps extends the forearm at the elbow. When one is concentrically contracting, the other is lengthening and relaxing to allow movement to happen. They also work together, along with many other muscles, to contribute to stabilization at the shoulder. The tendinous ends of the long heads of both biceps and triceps are part of the collective group of muscles that stabilize the ball of the humerus in the socket of the scapula.
Conclusions
The biceps brachii and triceps brachii are two important muscles for positioning our forearms. Those are key actions for all daily movements we do that involve grasping with our hands. We need our biceps and triceps to initiate movements from grabbing the steering wheel to typing. To better understand how these muscles contribute to those functional movements, it’s helpful to think about how they act in relation to each other.
References
Chaitow, L. and J. DeLany. 2011. Chapter 13: Shoulder, Arm, and Hand. In Clinical Application of Neuromuscular Techniques. Volume 1 (Second Edition). New York, NY: Churchill Livingstone Publishing.