What Causes Rod Shaped Lump Under Skin In Bicep?

I have a rod shaped lump under my skin. It started in my bicep while I was working, and then I rubbed it to feel it and felt that it was rod shaped and hard. Two to three more presses/rubs and it was gone! Today I woke to find the same thing on my calf. This one is not going away on rubbing. What is this?!