In reply to Rampikino:
Just my two cents on this subject, -coming from a fairly solid running background:
3:41 - 1500m
14:19 - 5000m
30:12 10K
currently aiming for a sub 2:30 marathon in my old age..
I do use treadmills occasionally, but there has to be a specific reason to use them. The overall effect your body gets from running outdoors is superior, particulalry the muscles - they get used to running on uneven surfaces, even a flat road has uneveness about it and wind resistance! However, there are some times when a treadmill makes sense. For example, if you are in a flat area and you want to run long hills or if outside it is icy and the risk of running outdoors doesn't make sense. I probably do a treadmill run once a fortnight as a tempo/threshold run for 30-40 which is run at a "comfortably hard pace" - roughly marathon pace cutting down to half marathon pace.
I actually find the pace on a treadmill harder work than say if I run the same session at the same pace on flat park roads/on the track. There are a few reasons for this from my perspective...
- It is boring..
- My feet tend to get sore on a treadmill for too long
- The air is stuffy
- The gym is warm
However, I do find there are some benefits. It makes you run economically, during a tempo/threshold run you do tire, however the treadmill stays constant, in fact I usually increase the pace towards the end. It makes you focus on running form and stay strong. Helps improve rhythm etc. I also work in London and will struggle to find somewhere to run at lunch where I can run 40mins uninterrupted at this pace - this I can do on the treadmill.
Like everything in life, moderation is the key... Don't do too much on the treadmill, but in my opinion it is not an easy option...