Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The torque generated by the muscle changes as the moment arm of the muscle changes during motion.
Reason (R): Instantaneous axis of rotation is the axis of rotation at any particular point in the Range of Motion (ROM). This axis moves during rolling or sliding motion.
In the light of the above statements, choose the most appropriate answer.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Torque = Force × Moment Arm Changing axis → Changing moment arm → Changing torque

Answer 1

The Correct Option is A

Concept:
Torque (\( \tau \)) produced by a muscle is given by: \[ \tau = \text{Force} \times \text{Moment Arm} \] The moment arm is the perpendicular distance from the axis of rotation to the line of action of the muscle force.

Step 1: Understanding Assertion (A).
As a joint moves:
• The angle between muscle and bone changes
• The perpendicular distance (moment arm) changes Thus:
• Torque produced by the muscle changes Hence, Assertion (A) is correct.

Step 2: Understanding Reason (R).
The instantaneous axis of rotation (IAR):
• Represents the axis at a specific moment
• Changes during joint movement due to rolling and sliding Hence, Reason (R) is also correct.

Step 3: Linking A and R.
Because:
• The axis of rotation shifts during movement
• The distance from muscle line of action to axis (moment arm) changes This directly explains why torque varies.

Step 4: Conclusion.
\[ \boxed{\text{Both A and R are correct and R explains A}} \]