Whenever you walk into a new gym, one space inevitably catches the eye: the main floor, filled with cardio machines of all kinds, rows and rows of ’em. And whether you’re there for a chill yoga class ...

Most gyms have an elliptical machine, otherwise known as a cross trainer. And chances are, someone's on it—and using it incorrectly. Sounds good, right? Ahead, fitness experts weigh in on everything ...