Muscle bump under ankle

Hello people!
I'm new here and I'm really excited to be part of the community!

But first off, I'm gonna explain a little problem I have and maybe someone knows some some facts about it. Since my childhood (I'm not certain about that) I have a bump (the size of a big walnut) under my both ankles. It's soft, full of veins (like the rest of the foot) and reacts exactly like a muscle (harden when I press my front part of my foot against the floor). Do you know what that is? It looks weird and I haven't seen it on anybody's foot so far (Ah, except my father's but smaller). Any Ideas?

[Yena H Do, DPM]

It's difficult to assess without seeing the ankle.
If the bump is towards the outer ankle but on top of the foot, it is the extensor digitorum muscle belly. You could have a very developed muscle there.
If it is below the outer ankle on the, it is a fat deposit.  Sometimes, it can be bigger on some than others.  If it is towards the inner ankle, it could be some sort of tumor...so, you would want to have it examined.  The fact that it is on both ankles, it sounds like a congenital formation (you were born with it and it is normal for you makeup).