The treadmill may not offer much in the way of natural scenery, unless you have a solar-powered version situated somewhere on a mountaintop. It does, however, offer numerous advantages over walking or running on the road. The surface is much softer than asphalt or concrete, weather isn't a factor, and you can control your pace with exquisite precision. All of these things make using a treadmill to get in shape over a 12-week period an appealing option.
The First Three Weeks
Assuming you are starting from scratch from a cardio standpoint but are otherwise in good health, plan to do four or five 20- to 30-minute walking workouts per week in your first three weeks on the 'mill. During this period, set the treadmill at 2.5 to 4.0 miles per hour with no incline. The specific speed you select should correlate to a heart rate of 70 to 85 percent of your maximum, which can be estimated by multiplying 0.88 times your age and subtracting the result from 206. If the treadmill you use doesn't have a heart rate-monitoring function, use your own monitor or take your pulse using your finger placed against the carotid artery in your neck. If these treadmill parameters do not allow you to work above 70 percent of max HR, incline the belt to a percent grade that does.
The Next Three Weeks
By this time, you should already be noticing some progress, with your heart rate and perceived exertion level being lower at a given speed -- and if applicable, incline -- than when you began. So it's time to up the ante.
In weeks four through six, you will still do four to five sessions of 20 to 30 minutes each, but will nudge the belt up to a 3 percent grade and keep the speed the same as it was at the end of week three. If you need to elevate the belt above 3 percent in order to keep your heart rate in the 70- to 80-percent-of-maximum range, do so, but keep the speed at no higher than 4 mph so that you can still power-walk without breaking into a run -- that comes later.
The Third Three Weeks
In weeks three through nine, you will introduce two new elements. One is substituting a very easy run for one of the incline walks, and the other is extending your longest session -- not the run -- to 40 or 45 minutes.
For the run, return the belt to 0 percent elevation and up the speed to 5 mph or faster -- whatever it takes to keep you in the previously noted HR range. Alternate jogging with walking if need be by lowering the belt speed to 4 mph or lower for five-minute periods, but try to make at least half of this workout a run. For the long session, you can walk the whole thing or alternate walking and jogging, depending on your comfort level; the key is to be on your feet a little longer than before.
The Last Three Weeks
Now you're ready to make running as big a contributor to your treadmill regimen as walking, if not a bigger one. If you are doing four workouts a week, starting in week 10, run at least two of your 20- to 30-minute workouts and walk no more than two, again raising the belt to as high a grade as is needed to ensure an aerobic workout while walking. If you're doing five sessions a week, try to run three of them. If you're feeling particularly energetic, you can run all or most of your 40- to 45-minute session, which in weeks to come you should strive to increase to an hour in five-minute increments.
So that's it. After less than three months, you'll be doing anywhere from 100 to 165 minutes a week of serious cardio -- and both seeing and feeling the results.
L.T. Davidson has been a professional writer and editor since 1994. He has been published in "Triathlete," "Men's Fitness" and "Competitor." A former elite cyclist with a Master of Science in exercise physiology from the University of Miami, Davidson is now in the broadcast news business.