Honestly I didn't know what to make the topic, but my question is this, if the majority of your races like HMs or FMs are on roads, would it hurt or help you to have the majority of your weekly runs on trails? 

  For example, if you run 4 days a week with 2 easy runs, 1 tempo and a long run, would it help or hurt if your 2 easy runs were on trails or if occasionally you replaced your tempo run for a trail run?

Only reason I ask is because someday I hope to run the majority of my mileage on trails, I love trails and they're just freaking awesome. But for the time being, 98% of my races are on the road, and there are only 2 HMs in Southern Indiana on trails and I believe only 1 FM (it will be quite a few years before I do that one). The first one was last Saturday, on pretty even terrain with no real hills, the 2nd one is June 8, 2013 in Hoosier National Forest called the Indian/Celina Challenge which is 3 choices, 26.2 miles, 13.1 miles or 8 miles. If I do sign up this year, it will be just for the 8 miles. The loop is 13.1 miles so you'd have to run it twice for 26.2, for the Half the elevation gain is 4,470 feet so I know there is no way I would be ready for that this year but I do plan on using that trail this summer for training. You can actually google the course buy typing Two Lakes Loop (either click on Indiana, or trail or Hoosier National Forest) to read up on it.

I think other than playing around on the trail this summer, I might start training for that Half this coming winter after my last Half for the year. Heck, I don't expect to run all of it, but it would be a cool experience . Anyways, my question is in the first or 2nd sentence.

I think trail running is a great way to train for a road race.

If you're running a weekly tempo run now, I would keep it and replace your easy runs or long run with trail.

I ran my first trail half in January, and have switched almost exclusively to running my long runs on trails.  Love, love it.  I have three more trail halfs I'm signed up for this year, all part of a series here in San Diego.  Not sure when I'll run another road race, but when I do, I'm certain all my trail training will benefit me in that race.

Yeah, I thought Audubon in Henderson was the only one with decent or crazy roller coaster hills around here, sadly there are demon horseflies out there during the summer. But I found that USI has some pretty crazy hills, not sure about horseflies yet..... they don't come out until temps reach 70+. Hoosier is a good 45 minutes away, so maybe after my May HM, I'll start heading there for my long runs. Then there are some nice, flattish trails around here for the runs where I might want to avoid a lot of elevation changes.

And right now my easy runs will have to stay on road until the sun starts staying up longer, because I am not able to get my weekly runs in until after 5 p.m.

Long Term Goal

• to be running ultras within 5-10 years
• a sub 8 min/mile for 5ks
• a sub 10 min/mile for Half Marathons

Short term goals

• to be running 30-35 mpw by the end of this year
• to have my long runs ranging between 12-14 miles or at least being able to run 13.1 miles with no real effort.
• a sub 9 min/mile for 10ks

I might have a lot I want to do at the same time, so it will take learning and being patient. This year I am aiming for 4 HM's, just because and next year I think I am going to train for that Half Marathon trail race at Hoosier National Forest.

Trails will help with agility and range of motion, not to mention strength on hills. If you run roads all the time, then you may have to do other exercises to get the same benefits of trails. At least that's my story and I'm stickin' to it.

Hey now Luke, there ain't nothing easy about roads!!

I am a strictly road racer, but I enjoy a good trail run every so often.  I think if you're looking to improve your times on roads, I would mostly train on roads (especially for quality workouts like tempo runs), however, I agree with lots of the other posters about the benefits you can get from trail running.  It does teach me some more agility, and step-for-step it is a little bit harder, effort-wise.  I am always a little bit more tired than usual after a trail run.  The biggest benefit to me is just having a nice change of scenery, sometimes it's good for the soul.  I like to drive out to local state parks to do my long runs in the summer.  Which makes me think of another benefit, we had a few days in the summertime that were over 90 degrees outside--going to the trails to run, the temperatures back there in the trees and shade are MUCH more tolerable.  It was at least 10 degrees cooler, which was a lifesaver at the time. Like somebody else said, it's a balance.  And if you enjoy them, they're certainly not bad for you.

Nice post from Jamezilla.

If most of your races are currently on roads, then you should do the vast majority of your speedwork on roads or on the track.  In my one ultra, another runner told me I had the long, loping stride of a road racer.  Of course, I am always a proponent of mixing things up.  Get out and run on some trails when you have the chance - especially for easy runs or for long runs.  Be cautious about going on a run with a bunch of elevation change and then calling it an easy run.  Those can put just as much fatigue in your legs as a hard track workout.

I would absolutely not replace my road tempo run with a trail run.  The point of a tempo run is to improve your body's ability to burn lactate as a fuel.  To do that, you need to stress that system and the best way to stress that system is through 20-50 minutes of constant effort.  That's nearly impossible to  do on many trails with all of the ups and downs.  Replacing your road long run with a long trail run would work as long as you adjust for time on feet and don't get focused on mileage.  An 8 mile trail run might keep you on your feet just as long as a 10 mile road run.

I like to vary it up and get some trail miles in as much as I can. Especially an LSD. Most of my races have been on roads, but I've been looking into doing more trails races as time goes by. It's just a totally different experience running on dirt, grass, gravel, etc. amongst the trees and alongside nature. I also love the challenges some trails provide along the way.