KIN 322 Kinesiology · Unit 2: The upper extremity · on Exam 2
2.2 Elbow and forearm
Study notes for Elbow and forearm in KIN 322 Kinesiology at Montana State University: the big ideas, a worked example, common mistakes and an exam tip. The same topic has endless practice questions and flashcards in Mathub.
Big ideas
- The elbow complex: humeroulnar (hinge; trochlea in the trochlear notch; the main flexion–extension joint), humeroradial (capitulum with the radial head; flexion–extension plus spin) and proximal radioulnar (pivot; the radial head turns in the annular ligament). The distal radioulnar joint completes pronation and supination, and the interosseous membrane passes force from radius to ulna.
- The carrying angle is a normal valgus of about 10–15° (often a bit more in females). The ulnar (medial) collateral ligament resists valgus stress and is injured in throwing; the radial (lateral) collateral resists varus; the annular ligament holds the radial head (a pulled “nursemaid’s elbow” in young children).
- Flexors: brachialis (a pure flexor on the ulna, working in any forearm position), biceps brachii (flexion and the strongest supination, best with the elbow at 90°) and brachioradialis (strongest in the thumb-up midposition). Extensors: triceps brachii (the long head also extends the shoulder) and anconeus.
- Pronators: pronator quadratus (the main one) and pronator teres. Supinators: supinator and biceps. Normal range: about 0–150° flexion, 80° pronation, 80° supination; the humeroulnar joint is close-packed in extension.
- Nerves: musculocutaneous (biceps, brachialis, coracobrachialis), radial (triceps, brachioradialis, supinator, wrist and finger extensors), median (pronators, most wrist and finger flexors), ulnar (flexor carpi ulnaris, part of FDP, most hand intrinsics). Lateral epicondylitis (“tennis elbow”) involves the common extensor origin; medial epicondylitis (“golfer’s elbow”) the flexor–pronator origin.
Worked example
Why is a chin-up (palms toward you) usually easier than a pull-up (palms away)?
Show the solution
With the forearm supinated, the biceps has a good line of pull and adds strongly to elbow flexion. When the forearm is pronated, the biceps tendon wraps around the radius and it is a weaker elbow flexor, leaving more of the work to brachialis and brachioradialis.
Common mistakes
- Calling biceps the strongest elbow flexor in every position. Brachialis is the workhorse.
- Placing pronation and supination at the humeroulnar joint. They happen at the radioulnar joints.
- Mixing tennis elbow (lateral, extensors) with golfer’s elbow (medial, flexors).
Exam tipQuiz yourself on each forearm position: which elbow flexor is strongest in supination, in midposition and in pronation?
Keep going in Mathub
Mathub is free for Montana State students: an endless quizzer with worked explanations, one-question lessons, flashcards, exam prep checklists, the class calendar with every deadline, a grade calculator and a study board for KIN 322.