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I am training for my first full marathon using your Novice 2 plan. I enjoy trail running and am lucky enough to have several trail systems to train on in beautiful, Southern (but hilly) Indiana. I am wondering, though, if I happen to schedule a trail race on a Saturday and the miles are a bit short for the planned long run (maybe only 2 or 3 miles short at most), do I need to worry about the lost miles? I figure the long run is about endurance and time on my feet. I know for a fact, that my trail pace is considerably slower than my road pace, but my level of physical exertion is higher. It will likely take me slightly longer to cover the fewer trail miles than it would the longer road miles. Is it okay to write off the extra few miles or should I make them up before or after the race?
I dunno. It's really up to you. Are trail miles more difficult than road miles? Some trails can be very fast: for example, the Prairie Path in the western suburbs of Chicago. Other trails that might be uneven or hilly or have logs to jump across, yes, they require more energy.
But I don't like to quibble and say that a trail 1.0-mile equals a road 1.136-mile. Too many variables. One measurement might be time. If it takes you 30 minutes to run 3.0 miles on a flat road, then 30 minutes of running would be its equal no matter the difficulty and distance of the trail. Inevitably in any training program, it is consistency that counts more than any other training variable. I like the fact that you are both training and racing on trails, so keep it up.