Answer for Fixing my stiff legs

Hello,
I am a pretty advanced player who is very confident with most strokes. However, recently my coach pointed out that my legs are too stiff, and because of that I use too much energy and cannot move as swiftly.
He advised me to relax my legs and lean on the toes more, but I do not really know how exactly I should do it. He recommended me to use the skipping rope, which I did for a bit of time, but it seems my legs are still pretty stiff even when I skip the rope. 
I think the problem here lies in my weak toe muscles. Could you please recommend some exercises to strengthen my toe muscles or generally lean on the toes more and keep my legs more relaxed?

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