Which event of the 'action potential' is indicated by the letter $\left(A\right)$ in the diagram?

Identify the 'place of hydrolysis of $\mathrm{ATP}\text{'}$ and the 'power stroke' in muscle contraction in the picture given below

The correct answer is :

Identify the region where all Na⁺ channels are reactivated but closed and all K⁺ channels are closed.