What Causes Electrical Shock Sensation On The Leg While Doing Exercise?

I am 62 years old and have exercised almost every day for many years. Currently I am using a sit down elliptical machine for 1 hour. Recently, I have been having sensations like electricity shooting though the front of my lower right leg when I exercise or even walk up and down stairs. I have no idea what could be causing this. Do you have any idea?