Which of the following movements in mammalian skeleton represent the leverage of the third order ltbgt (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 the weight of body on toes
D. Movement of the heac of femur in the acetabulum of pelvic girdle

Answer

To determine which of the movements in the mammalian skeleton represents the leverage of the third order, we need to analyze the options provided in the context of lever mechanics.

### Step-by-Step Solution:

1. **Understand the Types of Levers**:
- **First Order Lever**: Fulcrum is in the middle, with load on one end and effort on the other. Example: seesaw.
- **Second Order Lever**: Load is in the middle, with fulcrum at one end and effort at the other. Example: wheelbarrow.
- **Third Order Lever**: Effort is applied between the fulcrum and the load. Example: tweezers.

2. **Identify the Movements**:
- **Biceps muscle flexing arm at elbow**: The elbow joint acts as the fulcrum, the biceps muscle applies the effort, and the weight of the forearm and hand acts as the load.
- **Triceps muscle extending arm at elbow**: The elbow joint is the fulcrum, the triceps apply the effort, and the load is the weight of the forearm and hand.
- **Gastrocnemius muscle raising the weight of body on toes**: The ball of the foot acts as the fulcrum, the gastrocnemius applies the effort, and the load is the body weight.
- **Movement of the head of femur in the acetabulum of pelvic girdle**: This does not fit the lever classification as clearly as the others.

3. **Analyze Each Option**:
- **Biceps Muscle Flexing Arm at Elbow**: This is a classic example of a third order lever. The effort (biceps) is applied between the fulcrum (elbow) and the load (weight of the forearm and hand).
- **Triceps Muscle Extending Arm at Elbow**: This is more aligned with a first order lever, as the fulcrum is between the effort and the load.
- **Gastrocnemius Muscle Raising Weight on Toes**: This is an example of a second order lever.
- **Movement of the Head of Femur**: This does not fit neatly into the lever classification.

4. **Conclusion**:
- The movement that represents the leverage of the third order is **the biceps muscle flexing the arm at the elbow**.

### Final Answer:
The correct answer is **the biceps muscle flexing the arm at the elbow**.

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