Some find running or walking on a treadmill boring, but it has a number advantageous over an outdoor workout, among them protection from the elements, the ability to control your speed absolutely, and a soft, low impact surface. Perhaps the greatest edge the treadmill has over training outside is that you can run up a "hill" without having to pound your muscles and joints coming back down. But what is "percent grade" in terms a non-nerd can understand?
Finding Your Ideal Hill
Walk briskly or jog easily on a treadmill set to a 0 percent grade for five to 10 minutes to warm up. Depending on your fitness level, this could be anywhere from about 4 mph to about 6 mph.
Elevate the belt gradually to a walking or jogging pace that feels challenging, but not so difficult that you couldn't maintain it for at least 10 minutes if you want to. This should feel similar to your "favorite" hill outside, ideally one that takes you at least a couple of minutes to climb.
Note the percent grade on the treadmill console and stop the treadmill. Most treadmills go up to 10 percent; a few specialty treadmills reach 15 percent, but these are largely confined to pro-football training camps and the like.
Calculations and Comparisons
Turn on your calculator and input the percent grade. In geometry, this number is the slope -- "rise over run" -- multiplied by 100 to convert from a decimal to a percent. For example, if you climb an 8 percent grade, for every 100 feet you walk or jog, you gain 8 feet of elevation. 8/100 = 0.08, and 100*0.08 = 8 percent.
Calculate the angle in degrees corresponding to your selected grade. In trigonometry, the slope is the same thing as the tangent of this angle -- the length of the side of a right triangle opposite this angle divided by the side next to it. Do this by dividing the percent grade you punched in by by 100, then hitting the "inverse" button on your calculator followed by the "tangent" button.
Recognize that the percent grade and the angle are not the same thing -- many treadmill users are not aware of this. Using the example of an 8 percent grade, you would calculate an angle of 4.6 degrees. Even this feels quite steep; a 100-percent grade is not a climb straight up, but a climb of 45 degrees, too steep to run or walk up.
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.