When stimulus frequency is varied while intensity remains constant, what happens to twitch strength?

When the frequency of stimuli applied to a muscle is varied while keeping the intensity constant, the strength of the twitches can indeed vary. This variation occurs due to the physiological processes involved in muscle contraction and relaxation.

At low frequencies of stimulation, each twitched contraction is primarily independent, allowing enough time for the muscle fibers to relax fully between stimuli. As the frequency of stimulation increases, the time between stimuli decreases, leading to a phenomenon called summation, where subsequent twitches can build on the strength of previous contractions before the muscle has fully relaxed.

As the frequency continues to increase, the muscle may reach a point where twitches begin to fuse together, resulting in a stronger overall contraction, potentially leading to tetanus if the frequency is high enough. However, this process indicates that the twitch strength does not remain constant; rather, it is influenced by the rate of stimuli applied, allowing for variations in twitch strength.

Thus, the correct answer highlights the dynamic nature of muscle contractions in response to varying stimulus frequencies under a constant intensity scenario.