What is muscle fatigue?

Where are $ATPase$ enzymes located in a muscle fiber?

At which site do muscle fibers receive stimulation from a motor neuron?

Which of the following statements is true with reference to the structure of a muscle fibre?

Given below are two statements:
$Statement-I$: Plasma creatinine is produced during catabolism of creatinine phosphate in skeletal muscle contraction.
$Statement-II$: Creatinine phosphate provides a ready source of high-energy phosphate.
In the light of the above two statements, choose the most appropriate answer from the options given below.

Name the ion responsible for unmasking of active sites for myosin for cross-bridge activity during muscle contraction.