Which of the following is NOT a property of muscle fibers?

Contractibility is generally recognized as a key property of muscle fibers, allowing them to shorten and generate force in response to stimulation. This characteristic is essential for muscle function, enabling movements such as lifting, running, and any other physical activity that involves muscle contraction.

The other properties listed—elasticity, irritability, and conductivity—also play important roles in muscle fiber functionality. Elasticity refers to the ability of muscle fibers to return to their original length after being stretched, which is crucial for maintaining muscle tone and preventing injuries. Irritability, or excitability, describes the muscle fibers' ability to respond to stimuli from the nervous system, which is vital for initiating contraction. Conductivity pertains to the ability to transmit an electrical impulse along the muscle fiber, facilitating coordinated contractions.

Given this context, it's clear that contractibility is indeed an important property of muscle fibers, while the question asked for the property that is NOT characteristic of muscle fibers, putting it out of context with the other properties mentioned.