Call it power hiking or speed hiking, this is no slacker's workout, especially if you're at altitude. In fact, you can easily take hiking into the anaerobic zone if you really move it out. Because you're resisting gravity, hiking downhill works the legs eccentrically, just like skiing. Tyler shows good form here: He's walking fast, taking small steps, and keeping his shoulders a little forward-you don't want to be in the backseat. To take stress off your knees and for balance, try using ski poles. To work your heart harder yet, add 30-second intervals of higher-speed hiking or even running, or walk with your knees high.