Does treadmill training hurt your run fitness?

I don't think it does.  During the winter months I spend a lot of time on the treadmills at the gym, and I don't see any decrease in my ability to do certain mileage or pace efforts.  

One thing I would recommend is that if your treadmill has adjustable incline, set it to 1-2.5% incline which helps mimic normal, flat outdoor conditions.  

For me, the treadmill changes my running gait and I find it much more difficult. My feet, knees and shins hurt, and the 0% incline feels like 2% to me. When I go 2 or 3 miles it feels like I've gone 6 or 7. I guess I'm the opposite of most of you who've replied. But for me, yes, I feel like it certainly does not HELP my fitness.

I prefer 9.9 times out of 10 to get outside, as it's simply more natural and is less painful on my body. The only time you'll find me on one of those is when the there is an ice storm outside and have too many miles to do the indoor track, which is anywhere from 8-12 laps equaling one mile.

I'm not sure about your fitness but I'm sure it puts soft spots on your brain.

BOOOOOORRRRRING!!

Worse than the trainer

Very interesting.  As for your question: treadmill running is running.  It helps your run fitness!

Caveats: treadmills vary quite a bit in quality and design.  Some can be easier than 'real' running, but most are harder...like running in grass (their 'suspension' saps energy).

I'm very curious as to what really changed from your treadmill to outdoor running that you experienced.  Did you suddenly begin running outside when the temp was 90+?

Relative to what?  relative to not running? 

i.e. you're better off running on the 'mill than not running.  That said, unlike the above poster, I find 'mill running much easier than outdoors.  There are no hills, no curbs, the terrain is always perfectly even, the weather always perfect.  No wind, blistering heat, numbing cold or rain, sleet, hail or lightning.  To approximate running outside, I find that about a 1.5% grade makes my t-mill pace equivalent to my outdoor pace, but depending on your outdoor conditions, that would vary.  Also - you can run next to a friend at a completely different pace, and they always stay right with out.

Treadmills are terrific for some things- especially speed work and intervals.  You set that pace on the machine and it forces you to hit it exactly, which is terrific and controlled.  What they're the worst for IMHO is replacing a long slow distance run.  Just way too boring.

But- if you do all your training on a machine and venture outside for a race- you could be in for a big surprise.

That's what I would have thought too.  I remember worrying about a friend of mine who does 100% of his running on the treadmill all year.  In the 50+ age group, he tends to win half of the local sprint tris overall.  He runs about 6:00 pace in the tris on very rolling terrain.  I thought he was probably leaving a lot of performance on the table by not running outside.

Then last year I did 90% of all my running on the t-mill.  Not only do I run 1 min/mile faster at the same effort when I get on a flat outdoor surface, but I ran great this year and even so on hills.

Everyone seems to have a different experience with treadmill running.  Some people need a 1% incline to approximate running outside on flat ground.  I find that no incline is harder than running off the treadmill and I'm pretty sure it's because the treadmill surface is spongy.  But I like that because it protects my legs.

Maybe it's highly variable with the brand and model of treadmill?

I'm with Lisa on treadmills - no fun at all...

When you said you could barely do 3 miles, what was giving out?  Your legs or your heart?

If it was your heart/lungs, then I would venture a guess that you weren't working hard enough on the treadmill.   This winter make sure you monitor your heart rate.     While I think that running inside is the pits, I hear others say it's easier.  Make sure it's not too easy.

My other thought was pacing.  When you got outside, did you run too fast?  Do you have a tool to track your pace (Garmin, watch time with measured miles, etc)?  If not, you might have just run too fast without the benefit of the treadmill pacing you.

Just my two cents.  I think it's weird that you'd have that extreme of a reaction to outside.     I can see needing to get used to the difference, but wow.  

Running outside is so cool in the winter, I hope you can try it.  I mostly run inside when it's icey only, although occasionally just as a time saver too.  I live in Minnesota, so I could guess my winter is no better than yours.

Get a good headlamp and get out there. I just did a 10.5 mile run this evening in the dark. As long as you can find a trail there will be few other runners, and the temperature is great for running this time of year.

I'll run outside in the winter down into the single digits - the only issue arrives when there are big snow banks and I'm forced into the road. Only then will I revert to the treadmill at the gym.

I started out running on a treadmill several years ago then took it outside as much as possible.  One thing starting off on the treadmill did for me was help me learn to pace myself.  The belt moved at the speed I set it to and I quickly learned how I could run at X pace.  My last half marathon was an early Feb one so I did most of my midweek runs on a tready for safety sake since it would have been really dark and somewhat icy to run before/ after work. That was a PR race because I really followed the plan from RW to the points of when & where to do speed work. It didn't hurt to do it (though it was mind numbing BORING to do 9 miles on it one snowy day)

Since my return to running post injury I have been cautioned to not run on them as much.  Tried a couple months ago and my legs didn't like it much, used one the other day with a longer warm up and gradual increases in speed every 2 min without problems. 

Some comments in this thread notwithstanding, what I've seen on the subject notes that--biomechanically speaking--a treadmill actually requires slightly less work to cover the same "distance" at the same "pace" as running on a static surface...if I recall the analysis correctly, to get the equivalent work for the "same" workout requires adding 1% of incline to the treadmill.

That said, the difference is pretty trivial and road and treadmill running are essentially the same.  Main difference is the boredom factor on the treadmill as far as I'm concerned.

It does seem to vary by person, and the type of treadmill matters.  I can feel it between the LA Fitness treadmills and the and the ones in the workplace gym.  Star Trak vs Life Fitness I believe.  I like the Life Fitness ones at work better.  Less spongy so I keep some of the outdoor feel.  They can be boring, but it's up to you to make it more interesting.  I change the grade and/or pace every few minutes.  Most of the time it's a pattern and it's made a significant difference.  Still not quite as enjoyable as outside, but it's not awful.  Doing this also helps to avoid getting stuck in a rut.  I see too many people just set it to one speed (possibly warm-up first) and just go the rest of the time.

I find them to be a very useful tool for some things.  One, I live in Illinois, so the hills aren't very substantial.  I can bike to Wisconsin, but I can't run 20 miles out and then do hills.  There is a half mile hill right near me with 3% grade, but that's it.  Everything else is far shorter. I've set the treadmill to 3% for at least 45 min straight in the run.  Putting in 4-5% sections a few minutes long at times.  This helped out significantly in my ability to manage hills.  Pocono 70.3 had two sections of uphill at the far end of the out and back totalling at least a mile together at at least 5% each.  They didn't bother me much.  Adapting pace was easy.

I also tend to do speedwork on them. The surface is very consistent and controlled. I don't have to adjust for all the dinky ups and downs all the time.  I'll typically do all this at 0% (usually I run at 1% for easy ones) to maximize my speed.  Not to get the most distance, but to help with maintaining form at the higher pace when getting tired.  I need to get used to my legs moving that fast and being able to control it.

Treadmill does not hurt your running fitness.  It can actually help.  Doing intervals on the treadmill is a lot easier.  You can control the length and time pretty easily.

Depends on the person but I like running on the treadmill and watching a football game.  This allows me to get more training hours in.  (I would watch the game anyway )

I do run with the treadmill with a 1% incline.  I also believe the speed on the new treadmill we purchased to not be accurate.  So running 8 minute miles on the treadmill is much harder than running 8 minute miles outside.  This was not true with my old treadmill so I believe that is some issue with the treadmill speed.  I would imagine there are people with the opposite problem.

I also work on cadence and on the treadmill it is a lot easier.  I have the Garmin foot pod that works great on the treadmill.  

I don't think it can hurt your fitness, but for me there is nothing worse than a long run on the treadmill. The only time I was really injured running is when I was doing an 18-miler two winters ago on the treadmill. I lost concentration and fell off. If I'd been outdoors running and lost concentration I'd only slow down, on the treadmill you go flying.

I do find it useful to do intervals on the treadmill, mainly because access to a track around here is unpredictable.

You're going to get a hodgepodge (sp?) of answers on this one.  I started my return to fun fitness on a treadmill, mainly to give a softer impact to my joints etc.  I didn't have knee problems to begin with, just did it as preventative etc.  Over half my miles were on the treadie going into my first HM.  Ended up top 7% OA out of 4,500 people, not bad for indoor training.

I like doing intervals on the treadie, I basically ensure myself of holding a 6 minute mile for a quarter or half mile each time.  Also I can adjust the incline and get a little "hill" work in.  At the fitness club where I work out they have good machines, and not all treadmills are created equally.

I agree with running is running.  I try to have the same gait whether I'm outside or inside.  I'm sure it's not exact.  I think some people just have a hard time applying the same gait on the belt versus asphalt, trails etc.  Again, that might have something to do with the machine itself.

Agree with others, running is running.

OP:  You say that you cannot make it 3 miles after moving from t-mill to the road.  What is stopping you?  Fatigue?  Pain?  Do you eventually gain the ability, outdoors, to get beyond 3?  If so, how long does this take?

Of course the t-mill helps fitness (though I hate them and have sworn that I'll never run on one again...).  The issue here is just figuring out what is causing you problems moving back to the road.