A recent evolution in fitness machines has been the development of elliptical exercisers — a cross between an exercise bike and a ski machine, with a bit of stair climber thrown in for good measure. Your feet loop forward while your hands grasp the handlebars (also known as pedal arms) that move in sync with your feet. This is known as a natural elliptical movement — standing on the machine, putting your feet in the foot pedals, grabbing the stick-like handlebars, and pumping like a piston. Not all elliptical machines come with pedal arms, so be sure to gravitate toward ellipticals that can offer a full-body workout with arm-motion levers that move fluidly while your legs pump elliptically.

The legs receive a strong workout from the up-and-down stepper motion as you stride. The arms receive a satisfactory upper-body workout as one arm shoots forward while the other pulls back. Many elliptical exercisers work in reverse, which means you can work different muscles and experience some variety while walking backward.

Ellipticals provide great low-impact exercise for people with knee problems, but those in superior physical condition usually find the machines too easy.