There is a long-running (no pun intended) debate over whether runners should train on a treadmill or outside. In truth, you're capable of getting nearly the same exercise either way, so it may come down to your reason for running or your personal preferences. Some people simply don't like the "hamster wheel" feeling of running on a treadmill while others would rather not deal with weather conditions, pests, and uncertain terrain outdoors.
Of course, if it's all the same to you, there are several reasons you might choose one over the other. Here are just a few factors to consider when it comes to running on a treadmill versus running outside.
The time of day you have available for running could make a difference in where you choose to exercise. If you're running during your lunch hour or you have time during the day, then running outside may be feasible. In fact, you might have trouble finding machines at peak hours during the day such as before or after the average work day or during the lunch hour.
If, on the other hand, you have to schedule workouts during times of the day when it's dark outside, you'll probably feel safer running indoors, where you don't have to worry about running alone down a dark street, getting hit by a car, or turning your ankle on loose footing.
Both hot and cold climates can be detrimental to your running routine. When the temperature soars, you can easily overheat or get dehydrated, especially on long runs. If you live in a wintry climate, you have to be especially careful about dressing for the weather (so as to avoid hypothermia), and running carefully in slippery conditions.
In such instances, it's certainly easier and safer to run in a temperature-controlled environment like a gym or the comfort of your home. With proper planning and appropriate running apparel you can run outdoors in all kinds of conditions, and depending on the race you're training for, it may behoove you to train in similar conditions. However, it's easy to see why using a treadmill would be preferable.
There is some contention about whether a treadmill is or is not comparable to a "real" running experience, but with all the options for inclines, speeds, and resistance, you can almost certainly replicate running conditions on a treadmill, aside from weather conditions and loose terrain.
This generally comes down to personal preference. For some people, the time flies by when running on a treadmill, listening to a favorite playlist or watching a program on TV. Others feel satisfaction from breathing fresh air and watching the landscape go by. If you're not sure which you'll like better, simply try both and see what each experience has to offer.
You might feel like a major benefit of running on a treadmill is that you have complete control of your running experience. You can either run preset courses built into the machine or you can set your own course as you go, changing speed, incline, and overall difficulty to simulate outdoor conditions in a safe way.
Others find this to be detrimental to making progress in training. In nature, you might not get the exact number of hills or the level of incline you prefer - you have to work with the terrain in your area. That said, if you're training for a race, you're going to be in the same situation, subject to conditions beyond your control.
Some runners prefer to train in conditions in which they have no choice but to adapt to the terrain and weather they come up against. If you're just looking for an uninterrupted workout, perhaps the control afforded by a treadmill is right for you. If you'd rather test yourself in unpredictable conditions, running outside is more likely to deliver.
Although many treadmills offer settings that allow you to create your own course, simulating your preferred training challenges and potentially specific race courses, truly training for a race means running on pavement or trail conditions, preparing for the feel of the terrain and the weather you'll have to deal with outdoors.