Bending down to tie your running shoes, you sneak a peek at your watch. “Finally” you mumble to yourself. You flip the strings around your fingers and pull them tight. You pause to drink in the fresh air. “Woo hoo!” you shout in your head as you jump up to scramble across the parking lot and onto the trail. Electricity charges down your spine, ending in a shiver and tingling fingers. “Let’s roll” you smile to yourself. But once you start building up speed, things start to change. You first st...