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The triceps, or triceps brachii, is a large muscle on the back of the upper arm in humans and other vertebrates. It is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. The triceps is composed of three heads: the medial, lateral, and long head. All three heads cross the elbow joint, and the long head also crosses the shoulder joint. The triceps muscle contracts when the elbow is straightened and expands when the elbow is bent. This muscle can be strengthened through various exercises and is important for maintaining arm strength and stability.
| Characteristics | Values |
|---|---|
| Name | Triceps or Triceps Brachii |
| Description | A large, thick muscle on the dorsal part of the upper arm |
| Shape | Horseshoe |
| Function | Extension of the elbow joint |
| Parts | Medial Head, Lateral Head, Long Head |
| Innervation | Radial Nerve, Axillary Nerve |
| Blood Supply | Deep Brachial Artery, Superior Ulnar Collateral Artery |
| Reflex Test | Tapping the triceps tendon with a reflex hammer |
| Rupture Risk | Rare, typically only in anabolic steroid users |
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What You'll Learn
Triceps Brachii: the three-headed muscle
The triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It often appears in the shape of a horseshoe on the posterior aspect of the arm. The triceps is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, such as writing. The name 'triceps' is derived from Latin, with 'tri' meaning three, and 'cep' meaning head, referring to the three heads of the muscle: the long head, the lateral head, and the medial head.
The triceps brachii is the only muscle in the posterior compartment of the arm and represents the only constituent of the posterior muscle group of the arm, spanning almost the entire length of the humerus. All three heads cross the elbow joint, but the long head also crosses the shoulder joint. The triceps muscle contracts when the elbow is straightened and expands when the elbow is bent. The long head gets a further contraction when the arm is behind the torso due to how it crosses the shoulder joint. It is the muscle principally responsible for the extension of the elbow joint (straightening of the arm). The long head arises from the infraglenoid tubercle of the scapula. It extends distally anterior to the teres minor and posterior to the teres major. The medial head arises proximally in the humerus, just inferior to the groove of the radial nerve, from the dorsal (back) surface of the humerus, from the medial intermuscular septum, and its distal part also arises from the lateral. The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove. A portion of the muscle fibres also arise from the lateral intermuscular septum. Its attachment ascends obliquely, beginning from the lateral border of the humerus behind the deltoid tuberosity.
The triceps brachii can be trained in a variety of ways, including isolation and compound elbow extension movements. Isolation movements include cable push-downs, lying triceps extensions, and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push-up, bench press, close-grip bench press (flat, incline or decline), military press, and dips. The triceps can also be contracted statically to keep the arm straightened against resistance.
The triceps reflex, elicited by striking the triceps tendon, is often used to test the function of the nerves of the arm. This tests spinal nerves C6 and C7, predominantly C7. Axillary nerve damage can have an impact on the long head of the triceps brachii, so people with axillary nerve damage should undergo an assessment for the function of the LTB. If they demonstrate lost function, this indicates a poor prognosis, and early repair at three months is recommended. The triceps muscle can undergo reinnervation through a distal nerve transfer.
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Triceps exercises: static contraction movements
The triceps brachii is the prime elbow extensor and is responsible for elbow extension. The muscle is also active during other upper-body movements. For example, because the long head originates from the scapula, it also acts to extend the arm at the shoulder.
Isometric exercises are a form of static contraction movement. They involve holding the body in a position with no muscle or joint movement. The muscles are contracted but do not change length as you hold the position. For example, when you hold a plank, you’re contracting the muscles in your core, legs, and upper body to hold you up while remaining in the same position.
- Triceps dips: Sit on a chair or bench with your hands just outside your hips, with your knees bent or your legs extended straight out (harder). Keeping your hips close to the chair or bench, lower your body towards the floor, focusing on contracting your triceps muscle. Keep your shoulders down and away from your ears, and if you feel any discomfort in the shoulders, skip this exercise.
- Rope pushdowns: Using a cable machine with a rope attachment, hold the rope with your elbows bent at about 90 degrees and your elbows next to your torso. Extend your arms, taking your hands down towards the floor, spreading the rope slightly out on either side as you contract your triceps.
- Dumbbell overhead extensions: With your arms overhead, the long head of the triceps gets prioritised. This head is difficult to target otherwise, so it's a good idea to include some kind of overhead exercise in your triceps workout. You can do this exercise one arm at a time, or two arms at once, seated or standing.
- Close-grip bench press: While the bench press is usually a chest exercise, a close-grip press has been shown to target the triceps harder than wider grips, particularly when performed for heavier sets. Keep your hands around 8-10 inches apart, and tuck your arms in to decrease the amount of stress on your pecs and shoulders while increasing the demand on your triceps.
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Triceps tendon: testing nerve function
The triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It is composed of three heads: the medial, lateral, and long head. The triceps tendon can be tested to check nerve function.
The triceps reflex is often used to test the function of the nerves of the arm, specifically spinal nerves C6 and C7, predominantly C7. The test involves the following steps:
- The patient's shoulder and elbow are abducted to 90 degrees.
- The triceps tendon is tapped using a reflex hammer just proximal to the olecranon.
- The clinician observes the response to assess nerve function.
This test can be particularly important in cases of suspected axillary nerve damage, as it can impact the long head of the triceps brachii. If axillary nerve damage is present, an assessment of the function of the long head of the triceps brachii is recommended. In some cases, reinnervation of the triceps muscle may be possible through a distal nerve transfer.
It is important to note that triceps tendon injuries are uncommon, and ruptures of the triceps muscle are rare, typically occurring only in anabolic steroid users. However, tendinopathies can occur due to repetitive use of the tendon, leading to inflammation and pain. Therefore, when evaluating a patient with suspected triceps tendon injury, a thorough examination is necessary, and further investigations such as an ultrasound or MRI scan may be required for diagnosis and assessing severity.
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Triceps anatomy: heads, origins, and attachments
The triceps brachii is a three-headed muscle, with medial, lateral, and long heads. The triceps brachii is the only constituent of the posterior muscle group of the arm, spanning almost the entire length of the humerus. The medial head arises proximally in the humerus, just inferior to the radial groove, and from the dorsal surface of the humerus. The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove. The long head arises from the infraglenoid tubercle of the scapula, which is a rough area at the inferior margin of the glenoid fossa. Its attachment extends slightly above to the adjacent glenoid labrum and blends with the glenohumeral capsule of the shoulder joint, contributing to its stability. The medial head has an additional attachment to the posterior aspect of the medial and lateral intermuscular septum. The lateral head also has fibres that arise from the lateral intermuscular septum.
The triceps brachii gets its name from the Latin for "three-headed muscle of the arm". The three heads have different origins but converge to form a single tendon distally, which attaches to the olecranon process of the ulna. The triceps brachii is a large, thick muscle on the dorsal part of the upper arm, often appearing in the shape of a horseshoe on the posterior aspect of the arm. The triceps tendon is susceptible to injury, and any activity that overuses the triceps muscle can cause the tendon to become inflamed and damaged, resulting in pain and swelling near the muscle's attachment to the olecranon.
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Triceps function: extension and adduction
The triceps, or triceps brachii, is a three-headed muscle that is involved in two primary actions: extension and adduction. The triceps is the muscle principally responsible for the extension of the elbow joint, or the straightening of the arm. This is achieved through the three heads of the triceps: the long head, the lateral head, and the medial head. The long head is also involved in the adduction of the arm at the shoulder joint.
The long head of the triceps originates from the infraglenoid tubercle of the scapula and crosses the shoulder joint. When the arm is extended, the long head pulls on the glenohumeral capsule to produce the adduction of the arm. This action helps to prevent any displacement of the humerus. The long head also gets a further contraction when the arm is behind the torso due to how it crosses the shoulder joint.
The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just above the radial groove. The lateral head is active during the extension of the forearm at the elbow joint, particularly when the forearm is supinated or pronated. The lateral head is also used for movements requiring occasional high-intensity force.
The medial head arises in the humerus, just below the radial groove, and connects to the intermuscular septum. The medial head does not attach to the scapula and therefore does not impact the glenohumeral joint. The triceps extension is an isolation exercise that specifically works the triceps at the elbow joint. This exercise can be performed in a standing position, with the feet in a slight split stance, or in a seated position, or lying on a weight bench or the floor.
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Frequently asked questions
The triceps, or triceps brachii, is a large muscle on the back of the upper limb of many vertebrates. It is composed of three parts: the medial, lateral, and long head.
The triceps muscle is responsible for the extension of the elbow joint (straightening of the arm). It can also fixate the elbow joint when the forearm and hand are used for fine movements, such as writing.
Some exercises that target the triceps muscle include pullovers, straight-arm pulldowns, and bent-over lateral raises.
The triceps and biceps brachii are the main muscles controlling the movements of the elbow. The triceps is an extensor muscle of the elbow joint, while the biceps is a flexor muscle.
