Which statement correctly describes twitch summation and tetanus in muscle contraction?

Which statement correctly describes twitch summation and tetanus in muscle contraction?

• A. Twitch summation occurs when successive stimuli add to produce greater tension; tetanus is a sustained maximal contraction from high-frequency stimulation with no relaxation between stimuli.
• B. Twitch summation is a brief single contraction, and tetanus is a relaxed state.
• C. Twitch summation occurs only in cardiac muscle, whereas tetanus occurs only in skeletal muscle.
• D. Twitch summation and tetanus both require a decrease in intracellular calcium.

Answer: (A)