The action of the biceps brachii muscle on the hinge joint of the elbow is an example of which kind of lever system?


a. First class
b. Second class
c. Third class
d. Fourth class

Verified step by step guidance

1. Understand the types of lever systems: First-class levers have the fulcrum between the effort and the load, second-class levers have the load between the fulcrum and the effort, and third-class levers have the effort between the fulcrum and the load.
2. Identify the components in the elbow joint: The fulcrum is the elbow joint, the load is the weight of the forearm and any object being held, and the effort is the force applied by the biceps brachii.
3. Analyze the position of the components: In the action of the biceps brachii, the elbow joint acts as the fulcrum, the biceps apply force (effort) between the elbow (fulcrum) and the hand (load).
4. Determine the lever class: Since the effort is applied between the fulcrum and the load, this is characteristic of a third-class lever.
5. Conclude that the action of the biceps brachii on the elbow joint is an example of a third-class lever system.

Key Concepts

Lever Systems

A lever system consists of a rigid bar (the lever) that pivots around a fixed point called the fulcrum. Levers are classified into three types based on the relative positions of the load, effort, and fulcrum. Understanding these classifications helps in analyzing how muscles and joints work together to produce movement.

Types of Levers

There are three main types of levers: first class, second class, and third class. In a first-class lever, the fulcrum is between the effort and the load; in a second-class lever, the load is between the fulcrum and the effort; and in a third-class lever, the effort is applied between the fulcrum and the load. Each type has distinct mechanical advantages and applications in the human body.

Biceps Brachii and Elbow Joint

The biceps brachii muscle acts on the elbow joint, which is a hinge joint allowing flexion and extension. When the biceps contracts, it applies force to the forearm, which acts as a lever. This action exemplifies a third-class lever system, where the effort (muscle contraction) is applied between the fulcrum (elbow joint) and the load (weight in the hand).