Your arms contain many muscles that work together to allow you to perform all sorts of motions and tasks. Each of your arms is composed of your upper arm and forearm. Your upper arm extends from your shoulder to your elbow. Your forearm runs from your elbow to your wrist.

Before learning about the different muscles, it’s important to understand the four major types of movement they’re involved in:

  • Flexion. This movement brings two body parts closer together, such as your forearm and upper arm.
  • Extension. This movement increases the space between two body parts. An example of this is straightening your elbow.
  • Abduction. This refers to moving a body part away from the center of your body, such as lifting your arm out and away from your body.
  • Adduction. This refers to moving a body part toward the center of your body, such as bringing your arm back in so it rests along your torso.

Your upper arm contains two compartments, known as the anterior compartment and the posterior compartment.

Anterior compartment

The anterior compartment is located in front of your humerus, the main bone of your upper arms.

The muscles of the anterior compartment include:

  • Biceps brachii. Often referred to as your biceps, this muscle contains two heads that start at the front and back of your shoulder before joining together at your elbow. The end near your elbow flex the forearm, bringing it toward your upper arm. The two heads near your shoulder help with flexion and adduction of your upper arm.
  • Brachialis. This muscle lies underneath your biceps. It acts as a bridge between your humerus and ulna, one of the main bones of your forearm. It’s involved with the flexing of your forearm.
  • Coracobrachialis. This muscle is located near your shoulder. It allows adduction of your upper arm and flexion of your shoulder. It also helps to stabilize your humerus within your shoulder joint.

Posterior compartment

The posterior compartment is located behind your humerus and consists of two muscles:

  • Triceps brachii. This muscle, usually referred to as your triceps, runs along your humerus and allows for the flexion and extension of your forearm. It also helps to stabilize your shoulder joint.
  • Anconeus. This is a small, triangular muscle that helps to extend your elbow and rotate your forearm. It’s sometimes considered to be an extension of your triceps.

Your forearm contains more muscles than your upper arm does. It contains both an anterior and posterior compartment, and each is further divided into layers.

Anterior compartment

The anterior compartment runs along the inside of your forearm. The muscles in this area are mostly involved with flexion of your wrist and fingers as well as rotation of your forearm.

Superficial layer

  • Flexor carpi ulnaris. This muscle flexes and adducts your wrist.
  • Palmaris longus. This muscle helps with flexion of your wrist, though not everyone has it.
  • Flexor carpi radialis. This muscle allows for flexion of your wrist in addition to abduction of your hand and wrist.
  • Pronator teres. This muscle rotates your forearm, allowing your palm to face your body.

Intermediate layer

  • Flexor digitorum superficialis. This muscle flexes your second, third, fourth, and fifth fingers.

Deep compartment

  • Flexor digitorum profundus. This muscle also helps with flexion of your fingers. In addition, it’s involved with moving your wrist toward your body.
  • Flexor pollicis longus. This muscle flexes your thumb.
  • Pronator quadratura. Similar to the pronator teres, this muscle helps your forearm rotate.

Posterior compartment

The posterior compartment runs along the top of your forearm. The muscles within this compartment allow for extension of your wrist and fingers. Unlike the anterior compartment, it doesn’t have an intermediate layer.

Superficial layer

  • Brachioradialis. This muscle flexes your forearm at your elbow.
  • Extensor carpi radialis longus. This muscle helps abduct and extend your hand at your wrist joint.
  • Extensor carpi radialis brevis. This muscle is the shorter, wider counterpart to your extensor carpi radialis longus.
  • Extensor digitorum. This muscle allows for the extension of your second, third, fourth, and fifth fingers.
  • Extensor carpi ulnari. This muscle adducts your wrist.

Deep layer

  • Supinator. This muscle allows your forearm to rotate outward so your palm faces up.
  • Abductor pollicis longus. This muscle abducts your thumb, moving it away from your body.
  • Extensor pollicis brevis. This muscle extends your thumb.
  • Extensor pollicis longus. This is the longer counterpart to your extensor pollicis brevis.
  • Extensor indices. This muscle extends your index finger.

Explore the interactive 3-D diagram below to learn more about your arm muscles.

Several conditions can affect the muscles of your arm, including:

  • Muscle strains. This refers to any stretching or tearing of a muscle. They’re usually caused by an injury or overuse. Depending on the underlying cause, you might feel pain immediately. In other cases, it can emerge over several days or weeks.
  • Nerve compression. Sometimes, your muscles, bones, or tendons put too much pressure on nearby nerves. This is known as nerve compression or a pinched nerve. Your arm, especially your forearm and wrist, is a common area for this.
  • Shoulder injuries. Several of the muscles in your upper arm are connected to your shoulder. That means pain from a shoulder injury, such as a torn rotator cuff, often radiates down your arm.

It’s often hard to distinguish a problem with your muscles from an issue with your nerves or bones. However, muscle conditions often involve one or more of the following symptoms:

  • pain
  • a limited range of motion
  • swelling
  • weakness
  • muscle spasms
  • tingling

Muscle pain is often milder than bone or nerve pain. Bone pain tends to feel deep and penetrating, and nerve pain is often sharp or burning.

Follow the tips below to help keep your arm muscles healthy and avoid injury:

  • Exercise. Try to get at least 30 minutes of exercise most days of the week. To avoid injuries, make sure you begin by gently stretching. To build more muscle, gradually increase the frequency and intensity of your exercise. Allow your muscles to rest if you start to feel pain at any point while exercising. Not sure where to start? Try these five yoga stretches for arms.
  • Eat a balanced diet. Aim to eat a variety of whole grains, fruits, vegetables, and lean meats to support your muscles.
  • Take breaks. If you do anything that requires a lot of repetitive motion over a period of time, make sure you take frequent breaks. This will protect both your muscles and nerves from injury.