You can use any piece of cardio equipment or even do interval training outdoors. All you'll need are three variables to change the intensity of your intervals: speed, resistance and time. Outdoors, resistance can be provided by hills (the steeper the incline, the higher the resistance). Indoors, you can raise the incline on a treadmill or the resistance on a stationary bike. To monitor your effort, you can wear a heart rate monitor or use the RPE scale of one to ten ("rate of perceived exertion" where one is the easiest and ten represents an all-out, maximal effort).

The sample interval workout below uses a treadmill, but feel free to adapt it to your favorite mode of cardio.

• Minutes 0 to 5:
  RPE: 3 to 4 (3 to 3.5 m.p.h.)
  Incline percent: 0


• Minutes 5 to 9:
  RPE: 5 to 6 (fast walk or jog)
  Incline percent: 2


• Minutes 9 to 10:
  RPE: 8 (sprint)
  Incline percent: 2


• Minutes 10 to 12:
  RPE: 5 (recovery at moderate intensity pace)
  Incline percent: 0


• Minutes 12 to 14:
  RPE: 6 to 7
  Incline percent: Increase 2 percent every 30 seconds


• Minutes 14 to 16:
  RPE: 6 to 5
  Incline percent: Decrease 2 percent every 30 seconds


• Minutes 16 to 17:
  RPE: 8
  Incline percent: Increase as much as you can while maintaining speed


• Minutes 17 to 19:
  RPE: 5 (recovery)
  Incline percent: 0


• Minutes 19 to 21:
  RPE: 6
  Incline percent: 5


• Minutes 21 to 26:
  RPE: 3 (cool down)
  Incline percent: 0

If the above workout is too difficult, you can scale it back by making your rest intervals equal to your work intervals. Try walking for two minutes and then running for two. You can also shorten the program by doing only as many intervals as you can handle.

For a more advanced version of the sample workout, try one of the following: reducing your rest intervals, increasing the time spent in your work intervals, kicking up the speed or incline during the work intervals or adding more intervals to the total workout. Of course, don't try to progress in all of these variables at once!

Remember that this workout is based on your perception of effort. When you've tried it once, carefully assess how close you came to the recommended RPEs at each interval, and make the necessary adjustments. By continually updating your interval program and implementing it a few times a week (you can alternate with other cardio activity), you'll see real results.