For some, the hardest part of hitting the gym is lacing up their shoes. But for others, it's the actual exercisethat makes working out so excruciating. The labored breathing, sore muscles, and sweat dripping into your eyes can be a high or just one step above torture depending on which type of person you are. A new study aimed to determine what accounts for these differences, and it turns out your genetics might be to blame for how much you dread going for a run.