An elliptical trainer is a stationary machine that is a cross between a stair climber and a cross-country ski machine. Its pedals move in a circular, or elliptical motion, while the handlebars move forward and backward. By using both upper-body and lower-body movements against the machine's resistance, you get a total-body workout that can build strength, endurance and stamina.

People with knee or back issues find an elliptical especially beneficial. The smooth, rotating motion of the pedals is easy on your joints. Unlike running on a treadmill, where your legs do a lot of pounding, there is no jarring or high impact on the body because your feet stay on the pedals the entire time. You can even move the pedals backward for more of a challenge.

Ellipticals provide a significant way to burn calories. Someone weighing 150 pounds can burn an average of 300 calories in 30 minutes. To boost this caloric burn, you can increase the incline and speed. Another option is to do interval training, during which you increase the intensity for one minute, go back to a comfortable pace for one minute and repeat this cycle for 20 to 30 minutes.

An elliptical trainer will cost you $300 to $3,000 depending on the features. Higher-priced models have more settings and smoother mechanics.

When you're done, don't forget to stretch.