How much does road running fitness translate to trail performance, and vice versa?
In the last few years I have heard coaches and athletes throw around an idea that "trail running is a completely different sport than road running". I tend to think it might be a mis-interpretation of another statement: "ultrarunning is a completely different sport from traditional road running events". The latter has some merit to it, but I fear the former statement is leading to large misconceptions of who trail running is for and what it takes to succeed in trail running events, whether ultramarathon length, or more traditional distance events of 10K to trail marathon.
It's important to remember that at a certain level, running is running. This post is a quick explanation of how much road running and trail running fitness translate to one another, as well as the specific concerns that remain to be addressed for trail runners.
4 Ways Road and Trail Training Overlap
Aerobic (Cardiorespiratory) Fitness Development
At the end of the day, the largest component of performance in any endurance sport (except, perhaps, for elites) is aerobic energy metabolism. Large volumes of low intensity endurance exercise over months and years hone our body's aerobic fitness, meaning our ability to transport and use oxygen and efficiently produce energy. Perhaps the most important gain is increased fat oxidation rate (i.e. burning fat as fuel).
Regardless of whether we do our workouts on road or trail, if we're accumulating a volume of steady low intensity exercise, we're improving our cardiorespiratory fitness. Aerobic fitness is a component that trail runners can develop on the road, just as road runners can develop it on trails.
Running Economy
Economy is movement-specific efficiency that's separate from cardio respiratory fitness, but that also enables us to perform better. Road running lends itself to rapid development of economy because road running is much more repetitive and consistent in it's motion pattern, as we typically experience mild changes in incline/decline and there's rarely any technical elements, such as rocks or roots, to disrupt a smooth, stable, and efficient stride.
By making similar strides over and over in rapid succession as we do with road running, trail runners can develop flat running economy quickly on the road that will translate well to performance on the trail in two ways. The first is that trail runners may be able to run faster and easier through flatter, non-technical sections of trail. The second is that, following highly technical trail or steep hills, well-developed flat running economy enables trail runners to recover rapidly on the go where the trail does become flatter and less technical.
Road runners training on the trail sacrifice running economy but open themselves up to additional opportunities for their performance: resilience.
Resilience
Resilience is a loaded term, but what I mean here is essentially durability, or resistance to injury. Resilience in itself isn't a metric of performance, but what it enables is peace of mind and consistent training over the long-term due to lower incidences of injury, which could potentially disrupt training. Those two things are hard to quantify but nevertheless have substantial benefits for all athletes.
"Resilience in itself isn't a metric of performance, but what it enables is peace of mind and consistent training over the long-term due to lower incidences of injury"
A common technique employed by runners to develop resilience is strength training. There's lots to gain there, but the limit of most strength training is that we can only practice a few movement patterns and muscle groups in a strength session. By contrast, road runners who turn to the trail for occasional workouts will sacrifice some running economy but introduce their body to dynamic and varied running movements where they will activate muscles in novel ways compared to the repetitiveness of a road running workout. Improved muscle activation of balance and stability-focused muscle groups can play a significant role in the long-term injury resistance of road running athletes.
Trail runners turning to the road develop improved running economy as we already touched on, but if they are running trail a couple times per week on average, they don't stand to lose much in terms of their resilience.
Steady-Effort Practice
On varied and technical trail, the trail terrain is often more in control of the runner's effort than the runner themselves. Even if the effort level is consistent, the type of effort is often changing. Hiking a steep hill is a different sort of effort than running a descent, for example. In flatter, road running training, the opposite is typically true; runners have fine control over their effort as the terrain is pretty consistent.
For trail runners, tuning into a steady effort is an important skill that can get rusty when we're used to adjusting to varied terrain. In trail races, there's still a decent possibility of encountering longer stretches where we want to be able to lock into a steady effort. Races like the JFK 50 Mile demand that runners learn how to run technical trail to navigate the first 15 miles of the race, but they also need to be able to settle into a stride for the nearly 20 miles of level gravel path through the middle of the race.
Road runners don't have much to gain from swapping over to trail here. One could try to argue that learning how to increase effort for steep hills and then recover on the move is a benefit, but the type of hills we encounter on the trail tend to be too different in nature for much of a performance bump on the road.
4 Ways They Don't (For Trail Runners Only)
The benefits to trail runners of training on the road are significant, but they're not sufficient to lead to an athlete's best possible performance in trail environments. Below are the added complexities that trail runners need to prepare for that aren't necessarily addressed on the road. They're issues specific to trail running alone and that road runners typically need not think about.
Uphill Movement Economy
Running uphill recruits the leg muscles in a way that is substantially different from the muscle recruitment of flatter running events, but uphill movement economy can be developed by a similar method to running economy. In other words, the best way to get better at something is to practice it. The calf, quad, and glute muscles must respond in a much slower, but more powerful, contraction than the snappy, fast-contracting nature of a road running stride. Practicing uphill running in training will be important to enduring a race with significant uphill training, especially if that event is at high altitude.
Overall Uphill Speed
Uphill speed is multi-faceted, so road running training may translate to uphill speed in some ways, but not others. Part of overall uphill speed is aerobic fitness, which we've already established can be very well developed via road running. The grade of the incline matters a lot here. Research shows the energy cost of running uphill increases exponentially in relation to the steepness of the hill, as energy expenditure becomes less about moving us forward and more about opposing gravity. As mentioned in the Uphill Movement Economy point, at a certain incline the muscle recruitment changes dramatically, and road running alone could lead to insufficient muscular endurance in the glutes, quads, and calves as they're taxed in an increasing proportion. In other words, our aerobic fitness could be more than sufficient. We're breathing easy! Yet, we can't move any faster because of the cramps and burning in these overly taxed muscle groups. For this, uphill running workouts on trail or treadmill, or muscular endurance-oriented strength sessions at the gym for the legs, are almost a necessity.
"Uphill running workouts on trail or treadmill, or muscular endurance-oriented strength sessions at the gym for the legs, are almost a necessity."
Hiking Fitness
Hiking fitness requires a radically different movement pattern from road running, and it lends itself to energy efficiency and finer effort control. The hip flexors, calf, and tibialis anterior muscle (which runs along the shin) move through a larger range of motion in hiking movements than in running. With proper training, many trail runners can learn to hike at speeds that others must switch to a running gait to achieve. Benefits of hiking quickly can be a lower heart rate and less jostling of the body. The end goal as runners is to run in our races, but it's important to prepare for the reality that there will be points in most trail races where nearly all competitors are forced to hiking because of either steep grades or very technical trail. It's part of what makes trail running such a dynamic sport.
Downhill Pounding
Steep and extended descending is a completely unique aspect of trail running, and is a fitness that's hard to develop by any method other than exactly that; descending steeply on foot. The quads and calves face what's called eccentric muscle contraction, or the loading of a muscle while it is lengthening rather than shortening. This type of contraction is highly strenuous and damaging to muscle tissue, and triggers unique muscle fiber membrane adaptations to resist the damages of that high strain in the future. Gym-based lifting can help prepare for this, but at least small quantities of steep descending on a weekly basis are critical to our best performances in long and steep trail events.
Closing Thought
Where does that leave us? Trail running offers sport-specific cross training to road runners, which should be enough to convince road runners to get our on the trail once in a while both for the fun of it and for the benefit of greater resilience. Road running offering unique opportunities for both fitness and skill development to trail runners that are challenging to find training on the trail. So why limit ourselves to one type of fun?
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