The functional unit of the contractile system in the striped muscle is

What is a sarcomere?

$A$: 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.

'Oxygen debt' is the amount of oxygen required for

What is the source of energy for muscle contraction?

The myosin binding site is located on ..........