While some people prefer to distract themselves from their time on treadmills by reading, watching TV or listening to music, those who want to focus on an intense workout can also enjoy treadmills.
Speed, or pace, is an easy variable on treadmills. Setting yourself intervals at a higher speed is not only a good cardio workout, but it keeps you focused on when an interval is coming up, and when it is over and time to ease off.
Incline is the other variable that most treadmills can accommodate. Whether you prefer treadmills that pre-program a variety of "terrains" or treadmills that you manually change to a higher incline, the need to work harder and focus on your timing keeps you attentive to your workout.
An alternative to interval training on treadmills is pyramid training. This means that you set yourself a schedule for continually increasing your speed, or incline, for set time periods, reach your maximum, and then gradually decrease the intensity over those same steps.
Some people will even incorporate their treadmills into a larger workout that encompasses more variety. For example, if you normally work out at a walking pace and don't want to break into a run, instead try stepping off the treadmill for an interval of lunges or jumping jacks. Or in the slow times of an interval, pump hand weights to work on biceps and triceps.
To keep yourself involved with your treadmill workout, you can try visualizing a mental route. At the peak of your interval you might be climbing Mount Everest (or a nearby mountain you've hiked before), while during the slow times you could be enjoying the scenery of a lakeside path.
