Right now, though, Twilight was preoccupied with regretting the promise she’d made four days ago to eventually accompany Erin on her morning runs. At the moment, her legs felt like they were going to drop off. Or, possibly, burst into flame, she wasn't sure. Her chest heaved, and sweat ran thickly down her flanks, chest and face. She almost felt like she was drowning in it. Her hooves ached, her muscles burned, and she had a wicked stitch in her side that made breathing painful. And, to top it all off, the chill air was making her shiver. 