You hop on the treadmill, set your pace, and easily knock out a couple of kilometres.

Then a few days later you head outside to run the same distance. You try and to keep the same speed you did at the gym, but it destroys you.

What’s going on? Is it the weather? Your mood? Or is running outside genuinely harder?

The conditions are different outside

There are a couple of key reasons why running outside might feel harder than on a treadmill.

First, when you run outside, you push into the ground to propel yourself forward. But when you are running on a treadmill, the belt moves under your feet, helping with this propulsion (albeit very slightly). Basically, the machine does a small amount of the work for you.

Second, there’s air resistance outside. Research has suggested running on a treadmill is slightly easier because there is no air resistance caused by wind or even a slight breeze.

Studies show setting the treadmill to a 1% incline makes it more similar to running outside, by mimicking the difficulty added by air resistance.

Finally, the undulating terrain........

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