I'm always surprised just how much of a difference running outside is versus on the treadmill. The standard rule of thumb is that in order to more accurately mimic the outside environment on the treadmill, factoring in the amount of air resistance you'd meet, you should put the treadmill at a grade o 1.5%. Yet it still seems to me that even with this incline running on the treadmill is easier; I find myself able to go at a faster pace with less of an effort when compared to outdoors.

This could be attributed to a few reasons: 1- on a treadmill you're always going to be landing in exactly the same position. There are no variances in terrain, your footfalls are pretty much repetitions of the last because you aren't stepping on a rock, curb, or any other number of things. 2- you are always at the same cadence that you program into the treadmill. Outside you will inevitably always be running at a different speed as you naturally speed up or slow down whether you are making a turn, trying to make a light before it turns red, or getting chased by a rabid dog. Outside there are variable that will not allow you to be running dead on a specific pace like you can on a treadmill. 3- you do use different muscles on a treadmill because of the way the belt works. You're quads are taken completely out of the equation because the belt runs in a way that it will pull your leg backwards and then you will be heavily relying on your hamstrings to do all of the work. Outside you use both your hamstrings and your quads.

And so it seems that while convenient, running on a treadmill is not going to necessarily equate to the same times you would run outside. I'm not saying this is the case for everyone, there are those that swear by treadmill training and there was the woman from Alaska who won the US marathon trials a few years back after having to do all of her runs inside due to the weather. I guess the point is that if you are actively training and planning to race outside, a few runs on the treadmill isn't going to hurt, and it can prevent an injury if the outside conditions are much too icy or hazardous. Yet at the same time bear in mind that there is a difference, even if it is more subtle to some people; and when you do get back outside you want to keep that in mind. Usually after prolonged bouts of treadmill only running the first few times outside will leave you a bit sore because of the different muscles you use.