In terms of security, using a treadmill running indoors only caveat is to balance, some people ran out after the treadmill, there will be a feeling of dizziness. In addition, because the treadmill running belt width 40CM,45CM width and 47CM, even 47CM wide running belt, people run, they also have to really pay attention to your body's balance, if your foot stepped outside of the running belt, it is possible as a result of instability of gravity falls. Running outside, most people rarely can be found running the stadium, usually running up and down the road, and road train more people, there may be accidents. Runners need to inhale large amounts of oxygen, while outdoor automobile exhaust fumes in humans after inhalation is very harmful to the human body.
The weather was a factor in deciding whether running outside of, like fog, rain and snow are not suited to running outside, and a treadmill is not the limit. Best way is to run in the outdoors when the weather is good, the weather is bad when using a treadmill run in the indoor.