Increase in the chronaxie of a muscle signifies

• A. Significant factor
• B. Excitability of muscle decrease
• C. Intensity
• D. Constant current

Answer: (B)

The main concept here is how chronaxie reflects muscle excitability. Chronaxie is the minimum pulse duration required to elicit a response when the stimulus is set at twice the rheobase. If chronaxie increases, it means a longer pulse is needed to reach the threshold, so the muscle fiber is less easily excited. In other words, excitability has decreased.

The change is about timing of the pulse, not its strength. So increasing chronaxie does not indicate a change in current intensity or the use of a constant current; it signals that the tissue requires a longer stimulus to respond, i.e., reduced excitability.