Muscles of the Arm
Upper Arm Muscles
The upper arm contains two main muscle compartments: the ventral (anterior) compartment with three muscles and the dorsal (posterior) compartment with two muscles 1, 2.
Ventral (Anterior) Compartment
- Biceps brachii - the primary elbow flexor with two heads (long and short)
- Coracobrachialis - assists in shoulder flexion and adduction
- Brachialis - a powerful elbow flexor located deep to the biceps
Dorsal (Posterior) Compartment
- Triceps brachii - the primary elbow extensor with three heads (long, lateral, and medial)
- Anconeus - a small muscle assisting in elbow extension
The biceps functions to flex the arm, while the triceps straightens (extends) the arm 3. Architecturally, the triceps generates greater force than the biceps despite the biceps having longer muscle fibers, due to the triceps' higher physiological cross-sectional area 2.
Forearm Muscles
The forearm contains 21 distinct muscles organized into ventral (flexor) and dorsal (extensor) compartments 4, 5.
Ventral (Anterior/Flexor) Compartment
Superficial layer:
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor carpi ulnaris
Intermediate layer:
- Flexor digitorum superficialis (to all four fingers)
Deep layer:
- Flexor digitorum profundus (to all four fingers)
- Flexor pollicis longus
- Pronator quadratus
Dorsal (Posterior/Extensor) Compartment
Superficial group (4 muscles):
- Extensor digitorum communis
- Extensor digiti minimi
- Extensor carpi ulnaris
- Anconeus
Deep group (5 muscles):
- Supinator
- Abductor pollicis longus
- Extensor pollicis brevis
- Extensor pollicis longus
- Extensor indicis proprius 5
Clinical Relevance
The individual digital extensor muscles share relatively similar architectural structures, while the deep and superficial digital flexors are architecturally similar except for the small finger flexor digitorum superficialis, which is notably smaller and shorter 4. The brachioradialis and pronator teres, despite having nearly identical masses, demonstrate dramatically different contractile properties: the brachioradialis has long fibers at small pennation angles with only one-third the physiological cross-sectional area of the pronator teres 4.
These architectural differences are critical when selecting donor muscles for tendon transfers to restore thumb flexion, thumb extension, finger extension, and finger flexion 4.