Does running on trails require substantially more energy than running on roads?

Question

I've been running on trails for almost five years now. On my high school cross country team, we had a historic rule of thumb: Running at X-minutes per mile pace on trails requires the same amount of energy as running at (X-1)-minute pace on roads, for most reasonable paces (6:00-9:00 pace, in general).

I've read quite a few articles, and all seem to support the idea that trail running requires more energy. It makes sense; uneven surfaces are a lot more challenging to run on than flatter, even surfaces. However, I haven't found anything to support our rule of thumb - that is, that the difference in energy usage is so drastic. Have studies shown that running on trails consumes as much energy as running a minute faster per mile on roads, or is the difference less drastic?

My primary motivation for asking is that I've continued to run trails in college; as in high school, I run in a relatively hilly area. We run quite a bit more on roads than I did in high school, and so as I run higher mileage, I'm trying to figure out if I should run this much slower on trails in order to maintain a constant of effort in my training.

Answer 1

While this is a very limited study (i.e. n=1), it is the only actual quasi-scientific case study that shows trail running versus normal running, and it indicates that there is about a 12% increase in energy expenditure when running trails versus flat terrain.

Indirect calorimetry during ultradistance running

Now, I would consider this an interesting data point, but nothing more. They examined one person, and compared it against non competitive running on normal terrain for that same person, so there isn't really a way to quantify how much of the energy difference is due to race pace versus training.

However, the good thing about knowing this is that yes, there is more energy expenditure during trail running. This can easily be offset by using Gu gels or other similar energy gel/chew/drink while doing workouts on trails. This isn't really needed for workouts less than an hour, though, as long as your body stores are available and replenished after (in other words, eat right).

This chart gives a simplistic breakdown of the energy sources for various lengths of running, and claims that a gel of 2:1 glucose to fructose at 90 cals/hour is desired. (The link only goes to a bio, the only study I could find related to it was this one, which is just the abstract).

So in short, as long as you are fueled properly before, take some extra supplemental along on longer trail runs and rest/recover after, you shouldn't need to adjust your pace much to compensate for terrain.