Forearm Muscles: Flexors & Extensors – Anatomy, Actions & Locations
Forearm movement at the elbow joint is produced by muscles crossing the elbow. Key players:
Elbow Flexors (Anterior Compartment / Arm)
| Muscle | Origin | Insertion | Innervation | Notes |
|---|
| Biceps brachii | Supraglenoid tubercle (long head), coracoid process (short head) | Radial tuberosity, bicipital aponeurosis | Musculocutaneous (C5–C6) | Strongest supinator (forearm supinated); flexes elbow in any position |
| Brachialis | Distal anterior humerus | Coronoid process, ulnar tuberosity | Musculocutaneous (C5–C6) | Pure flexor; works in all forearm positions; main workhorse |
| Brachioradialis | Lateral supracondylar ridge | Styloid process of radius | Radial (C5–C6) | Forearm in mid-prone (hammer grip); assists flexion; paradoxical supinator/pronator to neutral |
Elbow Extensors (Posterior Compartment / Arm)
| Muscle | Origin | Insertion | Innervation | Notes |
|---|
| Triceps brachii | Infraglenoid tubercle (long), posterior humerus (lat/med heads) | Olecranon process | Radial (C6–C8) | Prime extensor; long head crosses shoulder (extends/adducts) |
| Anconeus | Lateral epicondyle | Lateral olecranon, proximal ulna | Radial (C7–C8) | Weak extensor; stabilizes elbow; abducts ulna in pronation |
Clinical Pearls
- Biceps tendon rupture: "Popeye" deformity, weak supination. Distal rupture = surgical repair often.
- Radial nerve injury: Wrist drop + weak elbow extension (triceps spared if high radial? No—triceps innervated above spiral groove).
- Tennis elbow: Extensor carpi radialis brevis tendinopathy (lateral epicondyle).
- Golfer's elbow: Flexor-pronator tendinopathy (medial epicondyle).
Note: Forearm muscles (wrist/finger movers) originate from epicondyles but act on hand, not elbow.
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