There’s nothing wrong with doing steady, moderate-intensity base runs on a treadmill, and in fact if you run indoors frequently over the winter, most of those runs should take this form. But you’ll also want to mix in some more interesting workouts, such as these three, if you want to become a better runner come spring.
In an interesting study, researchers placed subjects on a treadmill and asked them to walk or run and then gradually increased the incline. They found that at very steep inclines, the biomechanics of walking and running become indistinguishable. Essentially, walking at high intensity on a steep gradient is running, except that the impact forces are much lower than they are in level-ground running. For this reason, steep uphill walking makes a great recovery run. By walking for 20 to 40 minutes at a comfortable intensity on a 12-15 percent treadmill gradient, you get neuromuscular running practice without much impact, so that your muscles and joins can recover from previous running. Try it.
Runners and triathletes are often taught to obey the “hard-easy rule” in training. This rule stipulates that run workouts should either be very hard (say, 5 x 1000m at 5K race pace with 2:00 jog recoveries) or very easy (say, six miles at a pace that allows you to hold a normal conversation without getting winded). It’s true that this rule is helpful to the many runners and triathletes who, without it, fall into the trap of monotonous gray-zone training, where they feel compelled to make every run count, so they never go easy—yet precisely because they never go easy, they are also never able to go very hard.
But there is a place for moderately hard workouts, and the marathon-pace run is a good one. Warm up with one mile of easy jogging and then run anywhere from four to 12 miles (depending on where you are in the training process) at your ideal marathon pace. Doing this workout on a treadmill enables you to lock right on to that pace and stay there.
The workout format the exercise physiologists commonly use to determine VO2max is also useful as a powerful (if painful) fitness-boosting workout. Start by hopping on the treadmill and running easy for five to 10 minutes. Next, increase the belt speed by 0.5 mph and run for one minute at that speed. Now increase the belt speed by another 0.5 mph, hold the new speed for another minute, and continue in this fashion until you feel unable to run any faster. Reduce the belt speed and cool down. Note the maximum speed you attained and try to beat it when you repeat the workout in three or four weeks.