Treadmill vs. Running Outdoors

I am often asked these questions with regards to running and treadmills:-

1) Is running on a treadmill equivalent to running outdoors?
2) If i can run on the treadmill for 20 minutes, will i be able to run for 20 minuted outdoors?
3) Which is more effective to burn calories, running on a treadmill or running outdoors.

So i thought, its best that i clarify this topic properly so everyone understands why running on a treadmill is different than running outdoors. At first glance, the 2 may seem similar, but actually, there are quite a few differences.

Here are the answers to the questions:
1) Very similar, but not 100% similar
2) Not necessarily. Running outdoors is more challenging than running on a treadmill
3) Running outdoors at 6km/h for 20 minutes burns more calories than running 6km/h for 20 minutes on a treadmill.

OK, let me explain in more detail so all the answers make sense. Though the treadmill allows us to mimic a very similar movement of running, it is actually quite different. Running on a treadmill is actually easier than running outdoors. Why is it easier to run on a treadmill compared to outdoors?

For several reasons such as:-
a) There is no wind resistance when running on a treadmill. Because your body is stationary, you don't experience any wind resistance, which makes it easier.
b) The terrain is always uniform on a treadmill, where else running outside is never uniform. Because of this, your body is constantly working to adjust and balance itself to ensure that you can keep running and not fall down. Even this takes up extra energy... a little, but if your body is doing this constantly for 20 minutes, the little bit adds up.
c) Treadmill helps to propel you forward. In a treadmill, moving forward is assisted by the belt of the treadmill. Because of this, there is almost no energy used to propel you forward. Only energy being used is to keep your feet moving. When running outside, you have to move your feet and propel yourself forward, which makes it that much more taxing. Running on a treadmill is equivalent to running on the spot. I have read that adjusting the treadmill to a 1% incline will make it just as challenging as running outdoors.

Because of the reasons above, running outdoors is more challenging and burns more calories that running on a treadmill. Now, with that being said, it doesn't mean that all treadmills should be junked away immediately. There are some pro's that a treadmill has:

1) its not weather sensitive. Rain or shine, you can have a run at any time you want.
2) If you are a beginner to running, the treadmill provides you a safe and comfortable environment for you to build up your endurance / skill.

If you are training to be an outdoor runner (eg. running a marathon), then as far as possible, your training should be more outdoors than on the treadmill. Treadmill is a great place to get in a workout when the weather is not favourable, but overall, you should spend more time running outdoors.

So there you have it. The verdict on treadmill vs running outdoors. I still do the treadmill once a week, and i usually play with the incline and speed to make it more challenging and less boring. If you are a more serious athlete or fitness buff, than running flat on a treadmill for 20 minutes might put you to sleep. So feel free to play with the adjustments available to keep your workout challenging and effective for your fitness level. As usual, look forward to hearing your comments.