I have been running outdoors but today was pouring rain and barely above freezing, plus the wind was howling. So, I ran my 4 mile short run inside on the treadmill. It turned out to be a very good workout! I found that if I feel tired, the treamill belt just keeps right on going. Not quite as easy to slow down and relax like I get tempted to do when outside running. So, I think alternating between outside and the treadmill might not be such a bad idea. The weather up here on the North Slope of Alaska will force me to run indoors sometimes so I guess it is a good thing!