$ATP$ binding site is located on the

'Oxygen debt' is the amount of oxygen required for

Which of the following muscles act involuntarily?
$(a)$ Striated muscles $(b)$ Smooth muscles
$(c)$ Cardiac muscles $(d)$ Skeletal muscles

$M-$line passes through the centre of

$A$: Application of stimuli repeatedly just at the start of relaxation of a muscle fibre shows an increase in the extent of contraction initially and results in treppe or staircase phenomenon.
$R$: It can be attributed to the summation effect of the sub-threshold stimuli being given again and again.

The contraction of muscle of shortest duration is seen in