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I've found that by running comfortably on a treadmill for 30 minutes, I average 9 km/h, and I've tested this on several different treadmills.

When I go running outside, RunKeeper or some other tracking device tell me my pace is closer to 11 km/h , 12 km/h.

I'm wondering what the likely reason for this? Perceived difficulty is different between the two, device(s) are not accurate, having to propel yourself forwards means you naturally go faster??

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  • Your most likely culprit is heat. A lot of people run slower due to heat buildup, because you don't have the breeze of running to cool you off. I don't run slower, but I find that I can't run as long on a treadmill (or on a bike trainer for that matter) for that reason. – JohnP♦ Mar 24 '14 at 15:58
  • Maybe you are not running straight? If you are zigzagging, no treadmill will notice that, but a device you are carrying might just get it. – A-K Mar 24 '14 at 20:36
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Given that outside running utilizes different terrains, some steeper than others, it's possible that your terrain slopes downhill or you usually run with the wind, thus making your speed faster.

It could also be that the mechanics by which each device measures speed varies slightly (due to the materials used).

Lastly, given that on a treadmill, you are actually exerting more speed to counteract the backward movement of the belt (running outdoors doesn't have that), it's possible that your net speed is reduced, thus the values shown on the treadmills.

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  • No, you aren't running faster to counteract the belt. I forget where I saw it, but there were a bunch of physicists debating it and that was debunked. (If anything, the belt would make it easier, not harder). – JohnP♦ Mar 24 '14 at 15:57
  • @JohnP I haven't checked the articles on the subject; however, explain how the belt moving backwards will increase (and not decrease) a runner's speed. Thanks. – Kneel-Before-ZOD Mar 24 '14 at 16:10
  • Because the belt theoretically "pulls" the foot back faster, which makes it easier to maintain a higher speed. All of that was basically disproven, running on a treadmill is only very marginally different than running outside. – JohnP♦ Mar 24 '14 at 16:18
  • If the belt's moving backward while your feet's moving forward, how does that enable you to maintain a higher speed? To maintain the same speed, won't you need to go at a higher speed in order to counteract the backward pull? Basic Physics (and experience on treadmills) supports this theory; hopefully, you have an advanced Physics theory to disprove it. – Kneel-Before-ZOD Mar 24 '14 at 16:26
  • Your feet move forward in the air, not on the ground. Your feet move backward (in the same direction as the belt) to propel you forward. I don't have physics and never understood the argument, I just read it (Wish I could remember where). – JohnP♦ Mar 24 '14 at 16:51
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Treadmill running is much easier, unless it it one of the running road, and would be the reason for the difference in pace. The reason I say this, is because the treadmill does all of the work. All you are doing is keeping up with it.

The other reason, is outside the gradient naturally changes even under foot. Your body has to work more to move in a forward direction than on a treadmill. (ouside is like working on an unstable base in the gym - its harder) you also have the weather to contend with. Even a flat route outside would greatly use more muscles and effort.

Personally, I would only use a treadmill to warm up, or for a run when the outside option was not available.

  • running road treadmills are manually propelled ie you do the work. I think this could be more closely compared to outside running
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  • I agree with your answer, but in OP's case he ran faster outdoors, which goes against this explanation. I can only think that he might want to try a higher treadmill setting; do you have any other ideas for the reversed case? – meanderingmoose Jul 9 '14 at 18:46

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