Living in WI - Winter can be rough. Runs up to 1 hour are fine in any conditions outside. > 1 hour and if it is windy - I opt for TM and other times I just don't wan't to deal with the ice and snow.
I have run > 30 miles on the TM 12-15 times - 20+ more than I can remember.
My transition from TM to Road takes about 2 weeks to get used to the difference in how you run.
I made have run marathons (Houston 2006) with 2-3 total short runs outside and the rest mostly on TM. I set a PR at the time 2:47 at Houston that year.
Every runner is different - Some runners the right TM will be softer on joints and prevent inuries.
TMs water / bathroom are always close.
It just depends on how you can deal with the mental aspect. I would suggest:
1) Use at least a 1% to simulate outside. 2) Vary speeds and inclines to break up the run 3) Mix in outside running when ever possible.
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