In my opinion, using a 1-2 percent incline
to simulate the "wind resistance" created by your body moving forward through the air when running outside is one of the most
overblown "theories" in running. There are several other variables between road and treadmill running that are much more significant
than wind resistance. I think the three biggest ones are treadmill calibration, climate and terrain.
(1) Treadmill calibration. It can range
all over the place and make a particular 'mill easier or harder than running outside. The first 'mill I owned was a bargain
basement model that was very noticeably harder to run on when set at zero percent incline than running outdoors under comparable
climatic conditions. I had to adjust training paces to about 30 sec/mile slower than outside for an equivalent workout. Adding
a 1-2% incline would have just made it even more difficult than road running. OTOH, my current 'mill, that has a minimum incline
setting of 1%, and the 'mills I mostly use at the gym, when set to their minimum incline of zero percent, feel about the same
as running outdoors.
(2) Terrain. Unless you run on a track,
terrain outdoors is seldom dead flat, or zero percent. It's usually undulating. The undulations can range from subtle to mountainous.
Thus, either intensity varies throughout a run or pace has to be varied to maintain a constant intensity. Except for when
running hill repeats on a 'mill, how often do most people vary incline and pace to simulate variable outdoor terrains?
(3) Climate. It can be almost anything
outside. In most indoor settings, climatic control systems almost always maintain conditions at 70-72 degrees, 50-60% humidity
and no wind....and they are the same day after day. But, what if climatic conditions outside are ideal for running.....50
dry, windless degrees? Running in 50 degree temperature outside would be much "easier" than running the same pace in 70-72
degrees inside on a mill. So, should one jack up the back of the mill to simulate running downhill in that case to compensate
for not having the great outdoor conditions? OTOH, if it is 96 degrees with 90% humidity on a hot summer day, should one crank
the incline up to 5-6 percent to make running as difficult as outside? Actually, the 70-72 degree indoor environment really
doesn't make for good running conditions, especially for long distances or speedwork.
The "compensating for the lack of wind
resistance" theory implies that the lack of relative movement between your body and the surrounding air makes running easier.
However, I think that the lack of relative air movement over the body indoors can be a disadvantage, rather than a benefit,
which can make running harder. Air flow aids dissipation of body heat generated by running. If there is no air flow over the
body, cooling is reduced. And we all know that cooling is a significant factor in determining the ease or difficulty of running.
So, just what combination of outdoor
conditions is the incline adjustment intended to compensate for? And why? Very few days have ideal outdoor running conditions.
If most days outdoors are different, what's wrong with an indoor run on a 'mill being different than some set of "standard,
but undefined" outdoor conditions? Why cherrypick one relatively minor indoor/outdoor variable and recommend an incline adjustment
What do we do when outdoor conditions
vary? We adjust pace. What's wrong with doing the same on a 'mill to "compensate" for whatever the differences are between
indoors and outdoors? Making an incline adjustment to compensate for the lack wind resistance is simply adding one more factor
in selecting pace.
Bottom line....I think that using a 1-2
percent incline on a 'mill to specifically "simulate the wind resistance of running outdoors" is a meaningless thing to do.
I think that adjusting pace to get the training intensity that you want under the environmental conditions that you face,
whether on the road or the treadmill is more practical. And running indoors on a 'mill is simply another environmental factor
in choosing paces.
The problem with blindly following studies
that "prove" that running on a mill is easier than outdoors because of the lack of wind resistance and that adding 1-2% incline
to the mill will make them equal is that such studies are conducted under precisely controlled, lab-type conditions. However,
we run in the real world where conditions vary widely. I prefer to keep my mind open and adjust both incline and pace to achieve
the training effect that I desire for each specific treadmill run.
Physiology is another matter. Many people
experience foot or lower leg discomfort while or after running on a 'mill at zero percent incline. In such cases, using a
slight incline is smart. That just becomes an additional factor to consider in selecting treadmill pace.