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 ...

Whether through marathon training or simply getting my steps in, I've spent a lot of this year on the treadmill. My hips, knees, and ankles are feeling it, and my body feels tired. But I enjoy the ...