Which contractile protein of skeletal muscle is associated with $ATPase$ activity?

Which of the following movements in the mammalian skeleton represents the leverage of the third order,where the force is applied at a point between the fulcrum and the point of resistance?

In the resting state of muscles, where is calcium stored?

$A$: Muscle tetanus is the phenomenon of sustained contraction of a muscle due to a succession of nerve impulses/stimuli being received by it.
$R$: Many of our daily activities are due to tetanic contraction of muscles,such as holding a book.

Contractile proteins are found in

How many main types of muscles are there?