Just a quick little question. Ive noticed lately that on the way to my workout spot(1.5 mile walk to nearest park), I start to feel my blood going, just like when I get an adrenalin rush. And I've noticed that when I sprint across a crosswalk, aside from getting weird looks, my heart beats faster even though it was just about 20 feet. It's almost like my body is prepping itself with little action. Does anyone have any idea why this happens?