Running on a treadmill may look identical to running outside on a flat surface, but there are some significant differences between the two exercises that can have an effect on your body over time. If you want to simulate an outdoor run on a flat surface when exercising on a treadmill, you need to run at a slight incline.
Steeper inclines cause greater muscle activation in your lower body, and the greater the muscle activation, the more effective your workout will be. According to Lon Wilson, director of the Healthwalking program for the New York Road Runners Club, setting your treadmill to a 1 percent incline is ideal for simulating outdoor conditions.
An oft-cited study conducted by researchers at the Chelsea School Research Centre compared the oxygen consumption among subjects who ran outdoors and on various incline settings. According to their findings, a 1 percent incline most accurately reflected the energy costs of an average outdoor run over an extended period of time. Decreasing the incline reduced the energy cost of treadmill running compared to outdoor running, while increasing the incline above 1 percent resulted in significant increases in effort.
Even if you think you're running on a flat surface outside, it isn't going to be as consistently flat as a treadmill. Slight bumps and dips in the road, track or trail increase effort over time. Additionally, added factors such as wind resistance, friction from pavement, gravel or dirt and changes in direction can increase your effort.
The fast-moving belt on the treadmill actually reduces your effort slightly, since it pulls your feet out from under you rather than forcing you to push off the ground to create distance for your next stride. This pulling motion also changes the impact on your joints slightly by modifying your running form. In addition to setting a slight incline, you can compensate for these factors by paying attention to your running form on the treadmill. Try to keep your body upright and land with your feet directly under your center of gravity to keep a consistent impact force.
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