Treadmill Running

Running on a treadmill is a great way to build endurance while avoiding inclement weather and/or treacherous footing. Be aware that running inside is easier than running outside due to the lack of wind resistence and other weather conditions. Often your pace time inside will not translate outdoors so you might need to adjust your RPE level.
 

RPE stands for Rate of Perceived Exertion and is based on a 10-point scale.

10 = extreme exertion -- conversation is impossible

8 = high effort -- conversation is extremely labored

6 = optimum effort -- conversation is difficult, but possible

4 = medium effort -- conversation is easy to maintain

2 = warm up