Which of the following movements in mammalian skeleton represent the leverage of the third order lever (force applied at a point between fulcrum and the point of resistance) ?

Options

A. Biceps muscle flexing arm at elbow
B. Triceps muscle extending arm at elbow
C. Gastrocnemius muscle raising weight of body on toes
D. Movement of the head of femur in the acetabulum of pelvic girdle

Answer

To determine which movements in the mammalian skeleton represent the leverage of a third order lever, we need to understand the mechanics of lever systems. A third order lever is characterized by the force being applied at a point between the fulcrum and the point of resistance.

### Step-by-Step Solution:

1. **Understand the Lever System**:
- A lever consists of a rigid bar (in this case, the bone) that rotates around a fixed point called the fulcrum (the joint).
- In a third order lever, the force is applied between the fulcrum and the load (the resistance).

2. **Identify Components**:
- **Fulcrum**: This is the joint where the movement occurs. For example, in the arm, the elbow joint acts as the fulcrum.
- **Load (Resistance)**: This is the weight or resistance that needs to be moved. For example, if you hold a weight in your hand, that weight is the load.
- **Force**: This is the effort applied to move the load. In the case of the arm, the force is generated by the biceps muscle.

3. **Example of a Third Order Lever**:
- Consider the arm when flexing at the elbow.
- The elbow joint acts as the fulcrum.
- The biceps muscle applies force in the middle of the arm.
- The load is at the hand, where any weight is being held.

4. **Conclusion**:
- Therefore, the movement of the biceps muscle flexing the arm at the elbow is an example of a third order lever in the mammalian skeleton.

### Final Answer:
The movement that represents the leverage of a third order lever in the mammalian skeleton is the **biceps muscle flexing the arm at the elbow**.