The treadmill is the only machine in the gym that tells you what to do. On anything else (elliptical, bicycle, weights, classes, etc.) you do whatever you want and you get out what you put in. However, on the treadmill you have two choices: do what you said you'd do or fall off. Unlike the other ways to exercise where slacking off is a tempting choice, falling off a treadmill is not that appealing of an option.
Here are 3 treadmill workouts that only last 20-30 minutes that will burn serious calories, as well as training your muscular endurance, stamina, and speed.
Workout #1: A Less Boring Way to Run
What to Do: Run at a slow jog (around 4.5 - 5.5 mph) for 3 minutes, then bump it up to the highest speed you can tolerate for 3 whole minutes (which for most people is around 6.5 - 9 mph). Repeat this for 20-30 minutes.
Variations: If it's too tiring, take the lower speed down to a walk before you monkey with the top speed. Keep the top speed as high as you can, then give yourself a break on the recovery front. This being said, you aren't allowed to stop either. Keep moving the entire time.
Why This Helps: Stamina is one of the hardest parts of exercise. When you do stuff, you get tired. Doing intervals gives you the opportunity to push yourself mentally and physically, while still getting that rest between high intervals. This also teaches your body how to do "active rest", which basically means recovering without laying on the floor and whimpering.
Workout #2: The Hills are Alive with the Sound of BURNING LEGS
Targets: Muscular Endurance
What to Do: Set the treadmill to the fastest speed at which you can walk instead of jog. Alternate between 1 minute at an incline of 0% to 5%. Then do 2-3 minutes at the highest incline you can take. Note: even though you don't touch the speed, you will probably want to switch into a jog.
What NOT to Do: Never, never, never, never, ever touch the treadmill. Don't hold on. Don't even think about holding on. Just don't. Seriously. Hands off. No matter how badly you want to.
Why This Helps: Normal treadmill running is more focused on speed and stamina. Adding the super duper incline puts more emphasis on muscles like the quads and glutes. It also changes the exercise up so that those who are used to running can break through any plateaus they might be hitting with a test of a new type of stamina.
Workout #3: Whooooooosh...Where'd You Go?
What You Do: Start at a normal running speed (5 to 6 mph). Run for 30 seconds then hop off (leaving the belt running) and rest for 30 seconds (and only 30 seconds). After completing 3 successful sprints (i.e. you ran without holding on for the whole 30 seconds), up the speed either by .5 mph or 1 mph. After another successful 3 sprints, go up another .5 to 1 mph. Repeat until you can't make it through the full 30 seconds.
One Skill To Master: You will have to jump on and off the moving treadmill for this one. It is scary at first, but no matter who you are you can do it. Grab the handrails during the switches, and slowly move your feet onto/off of the moving treadmill belt. There's nothing to be afraid of: you simply can't fall off because most of your weight is in your hands and you don't have to let go until you're confidently on your feet. So quit whining and do it. Seriously. You can do it.
Homework: Do one of these workouts in place of your normal cardio. It will be both less boring and more beneficial (not to mention more exhausting...I mean rewarding).
Note: If you try all three in one week you get 5 official BurnIt Athletics badass points.