Muscles of the Arm: Anatomy and Function

Nothing beats a great pair of arms. Although abs and quads look great at the beach, developing your arm muscles can turn heads even when you are fully clothed. Most people assume that building your arm muscles is simple. However it takes more than just curls and tricep kickbacks. If you increase your understanding of how these muscles work, you will be able to strengthen and build them more effectively.

Bones of the Arms

The upper arm includes the area between the shoulder and the elbow joints. The bones of the upper arm include:

  • Scapula. The scapula is commonly referred to as the shoulder blade. It helps attach the arm to our torso.
  • Clavicle. The clavicle is commonly referred to as the collarbone. Similar to the scapula, it is responsible for attaching the arm to the torso. Additionally, it helps distribute force from the arms to the rest of our body.
  • Humerus. This is the long bone of our upper arm. It is located between the scapula and the elbow joint.

The forearm is the lower section of your arm. It is the area between your elbow joint and your wrist. It’s two major bones are the radius and the ulna:

  • Radius. The radius is found on the side of your forearm closest to your thumb. It twists around the ulna based on the position of the hand.
  • Ulna. The ulna runs parallel to the radius. It is on the outside of the forearm closest to the pinky finger. Unlike the ulna, it remains stationary and doesn’t twist.

Joints of the Arm

The upper arm contains several joints, including:

  • Acromioclavicular joint. This is the joint that connects your scapula to your clavicle.
  • Glenohumeral joint. This joint connects the scapula to the humerus.
  • Sternoclavicular joint. This joint connects the sternum to the clavicle.

The elbow joint is the area where the humerus bone of the upper arm connects with the radius and ulna bones of the lower arm. Interestingly, the elbow joint is actually composed of three seperate joints:

  • Ulnohumeral joint. This joint is responsible for connecting the humerus to the ulna.
  • Radiocapitellar joint. This joint connects the radius to the humerus.
  • Proximal radioulnar joint. This joint connects the radius and the ulna. It is responsible for the rotation of our hands.

Muscles of the Arm

There are four main muscle groups of your arms: biceps, triceps, forearm flexors, and forearm extensors. Each muscle group consists of a variety of muscles that help us flex and extend our arms. Additionally, they can help us move our arms and hands towards and away from our bodies.

Biceps

Bicep Muscle. Bicep Branchii, long head and short head. Arm Muscle

The biceps is a large muscle group that is located on the front of the upper arm. It is found between your shoulder and your wrist. The biceps is a two-headed muscle and is the main flexor of your forearm. It is composed of the short and long head of the biceps brachii. The short head starts from the scapula and attaches to the forearm. Similarly, the long head starts from the scapula and attaches to the forearm. Both these muscles are responsible for flexing the elbow, flexing and bringing the shoulders forward, and finally it helps us turn our wrist.

Triceps

Triceps brachii. Arm Muscles.
Red is the long head, yellow is the lateral head, green is the medial head.

The triceps are medically referred to as the triceps brachii, latin for three headed muscle of the arm. This muscle is the large muscle on the back of our upper arm. It is composed of three muscles: the medial, lateral, and long head. Each of these muscles helps us with the extension or our elbow joint, or the straightening of our arm. The long head starch from the scapula and attaches to the ulna. The lateral head starts from the humerus and attaches to the ulna. Finally, the medial head starts from the upper humerus and attaches to the ulna. These muscles are responsible for extending the forearm. The long head allows us to extend our shoulders and rotate our wrists away from our body.

Forearm Flexors

Superficial layer of the forearm. Muscles of the arms. Forearm muscles.

The forearm contains significantly more muscles than your upper arm. The muscles are classified into both an anterior (front) and a posterior(back) components. Additionally, each component is divided into three layers: Superficial, intermediate, and deep. The superficial layer is closest to the surface, the intermediate layer lies below the superficial layer, and finally, the deep layer is underneath the other two. The forearm flexors lies on the bottom of our forearm and is mostly responsible for flexion of our wrists and fingers. Additionally, it helps with the rotation of the forearm.

Superficial Layer

  • Flexor carpi ulnaris. This muscle pulls the wrist towards your body.
  • Palmaris longus. This muscle flexes your wrist. Interestingly, not every person has this muscle.
  • Flexor carpi radialis. This muscle helps us flex our wrists as well as move the wrist and hand away from our body.
  • Pronator teres. This muscle is responsible for the rotation of our forearm. It allows the palm of our hand to face our body.
Intermediate muscles of the wrist. Muscles of the lower arm. Muscles of the wrist.

Intermediate Layer

  • Flexor digitorum superficialis. This muscle is responsible for the flexion of our second, third, fourth, and fifth fingers.

Deep Layer

  • Flexor digitorum profundus. The muscle helps with the flexion of the fingers. Additionally, it allows us to move our wrist towards our body.
  • Flexor pollicis longus. This muscle flexes the thumb.
  • Pronator quadratura. This muscle supports the pronator teres to help rotate the forearm.

Forearm Extensors

Deep muscle of the wrist. Muscles of the lower arm. Muscles of the wrist.

The forearm extensor muscles are located on the top of the forearm. They are mostly responsible for the extension of our wrists and fingers. Unlike the forearm flexors, this component does not have an intermediate layer.

Superficial Layer

  • Brachioradialis. This muscle helps us with the flexion of our forearm at our elbow.
  • Extensor carpi radialis longus. This muscle helps us move our wrist away from our body. Additionally, it is responsible for extending the hand at the wrist joint.
  • Extensor carpi Radialis Brevis. This muscle is the shorter, wider counterpart to the extensor carpi radialis longus.
  • Extensor digitorum. This muscle is responsible for the extension of our second, third, fourth, and fifth fingers.
  • Extensor carpi ulnari. This muscle helps us move our wrist towards our body.

Deep Layer

  • Supinator. This muscle is responsible for the rotation of our forearm so that our palm faces up.
  • Abductor pollicis longus. This muscle helps us move our thumb away from the body.
  • Extensor pollicis brevis. This muscle helps us extend the thumb or straighten it.
  • Extensor pollicis longus. This is the longer counterpart to the extensor pollicis brevis
  • Extensor indicis. This muscle is responsible for the extension of our index finger.

Conclusion

The arm muscles are an extremely important muscle group that helps us flex, extend, and rotate our wrists. Additionally, they help is move our fingers and thumb. Understanding the function of each of these muscles will help make your training more effective. You can target a specific head of your biceps or triceps to ensure that your arm muscles are developing evenly.

Follow me on Twitter, Facebook, Instagram, or Pintrest for more!

Leave a Reply