Walking a mile and getting the best workout in that mile will be different for different people. There are three key factors in a workout designed to reduce fat and increase fitness. These factors are pace (in miles per hour), angle of climb (from flat to various inclines) and duration of the total walk.
Walking each mile in 30 minutes
Two miles per hour is a slow treadmill workout, but is still quite valuable. At this pace, a mile is covered in 30 minutes. Of course, an hour workout at this pace would complete 2 miles. While estimating calories burned without knowing a person’s lean body mass and heart rate during the workout is imprecise, a 150 pound person might be expected to burn 290 calories on a level treadmill at 2 miles an hour over the course an hour.
Combined with a careful diet, even 3 or 4 days a week at an hour a day on the treadmill at 2 miles an hour should make a good contribution to weight reduction and overall fitness.
Also, the number of calories burned can be increased without walking farther or faster simply by changing the elevation of the treadmill. For example, increasing the elevation to 5% should increase the calorie burn for that same 150 pound individual from about 290 to about 340.
Walking each mile in 20 minutes
If you feel comfortable and safe going a bit faster, a better workout is available in the same one-hour time period. By increasing the treadmill rate to 3 miles per hour, that 150 pound person would burn about 400 calories per hour on a level treadmill. Increasing the angle of the treadmill to 5 degrees increases the calorie burn to about 474 calories.
Since a pound of fat can be lost by burning 500 calories a day for a week, all but 26 calories of that objective can be achieved each day just on the treadmill if it is operated at the foregoing rate, duration and elevation.
An even faster treadmill walk is established by some training organizations. Their rate is 4 miles per hour or a mile every 15 minutes. At the same 5% elevation, this higher pace dramatically increases the benefit: 400 calories for a 100 pound person, 608 calories for the 150 pound example used early, and 811 for a 200 pound person. This level of workout should only be undertaken by those already physically fit.
Walking a mile and stopping
Conversely, walking a single mile at any pace without continuing the workout reduces its cardiovascular benefit. The reason is that each person, depending on their lean body mass and heart rate, needs a warm-up period of walking between 15 to 30 minutes before they experience more efficient aerobic exercise.
As a result, most of a one-mile treadmill walk will be inefficient. A full one-hour workout will be much more efficient because most of the aerobic gains take place after the warm-up period.