Which phase occurs first after a stimulus and shows no measurable tension due to EC coupling processes?

• A. Latent period
• B. Contraction period
• C. Relaxation period
• D. Tetanus phase

Answer: (A)

The question tests understanding of the delay between a stimulus and the start of force production created by excitation-contraction coupling. Immediately after a stimulus, the muscle fiber goes through a latent period where there is no measurable tension yet. During this brief interval the action potential travels, calcium is released from the sarcoplasmic reticulum, and the molecular machinery begins to prepare for contraction, but cross-bridge cycling hasn’t produced force to measurable levels. After this latent phase, tension rises during the contraction period as more cross-bridges form and generate force. Relaxation occurs later as calcium is pumped away and cross-bridges detach, reducing tension, and tetanus is a sustained contraction from rapid successive stimuli, not the initial delay.