Which set of terms describes the phases of a muscle twitch?

• A. Latent period, contraction, relaxation
• B. Contraction, relaxation, fatigue
• C. Treppe, tetanus, fatigue
• D. Activation, plateau, decline

Answer: (A)

The main idea is the sequence of events that happen in a single muscle twitch. After a stimulus, there’s a brief latent period where nothing is yet visible as calcium is released and the muscle prepares for contraction. Then the contraction phase begins, during which actin-myosin cross-bridges form and generate tension. Finally, relaxation occurs as calcium is pumped back and cross-bridges detach, returning the muscle to its resting length and tension.

This is why the described set is the best: it matches the actual timeline of a twitch from start to finish. The other options bring in concepts that don’t describe a single twitch’s phases. Fatigue refers to reduced force with repeated stimulation, not a phase of one twitch; Treppe and tetanus are phenomena seen with repeated stimuli or high-frequency firing, not the sequence of a single twitch; Activation, plateau, and decline don’t reflect the typical progression of latent period, contraction, and relaxation.