Question

Which of the following is the spurt muscle?

• A. \( \text{Brachioradialis} \)
• B. \( \text{Brachialis} \)
• C. \( \text{Pronator Teres} \)
• D. \( \text{Coracobrachialis} \)

Hint:

\textbf{Biomechanics: Spurt and Shunt Muscles.} Understanding the functional classification of muscles based on their attachment points relative to the joint axis helps in analyzing joint movements and stability. Spurt muscles are movers, while shunt muscles are stabilizers.

Answer 1

The Correct Option is B

Spurt and shunt muscles are classifications based on their attachment relative to the joint axis of movement and their primary function during joint action. Spurt muscles have their origin far from the joint and their insertion close to the joint. Their primary role is to initiate movement and produce a large range of motion. They have a large rotary component of force. Shunt muscles have their origin close to the joint and their insertion far from the joint. Their primary role is to stabilize the joint and resist dislocation. They have a large translatory (parallel to the bone) component of force. Considering the muscles around the elbow joint: Brachialis: Originates from the anterior surface of the humerus (relatively far from the elbow joint axis) and inserts onto the coronoid process of the ulna (close to the elbow joint axis). This arrangement makes it a spurt muscle, primarily responsible for flexing the elbow through a large range of motion. Brachioradialis: Originates from the lateral supracondylar ridge of the humerus (further from the elbow joint axis than brachialis) and inserts onto the styloid process of the radius (further from the elbow joint axis than brachialis). It acts as both a spurt and a shunt muscle, contributing to flexion and also providing some stability. Pronator Teres: Originates from the medial epicondyle of the humerus and the coronoid process of the ulna (close to the elbow joint axis) and inserts onto the lateral surface of the radius (further from the elbow joint axis). It primarily pronates the forearm and assists in elbow flexion; its shunt component is more significant for elbow joint stability during pronation. Coracobrachialis: Originates from the coracoid process of the scapula (far from the elbow joint) and inserts onto the medial surface of the humerus (far from the elbow joint). It primarily flexes and adducts the shoulder joint and has no direct spurt or shunt action on the elbow. Therefore, the brachialis is the clearest example of a spurt muscle among the given options for elbow flexion.