The muscles immune to fatigue are

How many main types of muscles are there?

$A : Ca^{2+}$ plays an important role in muscle contraction.
$R : Ca^{2+}$ combines with the troponin chain,displacing tropomyosin and allowing the myosin head to combine with actin to form an actomyosin complex.

Black bands of myofibrils are known as

Globular protein which masks active sites on $G$-actin is :-

In striated muscle contraction: