The Science of Trail Running Biomechanics

This article originally appeared on Trail Runner

The human body is a system in motion. Each muscle, tendon, bone, and ligament aims to function most efficiently. Biomechanics is an area of study in the larger practice of Kinesiology. According to Dr. Alena Graboski, an Associate Professor of Biomechanics at the University of Colorado in Boulder and an avid trail runner and skier, "Biomechanics is the meshing of physics and physiology to understand better why we move the way we do." She explains that in running, this science can determine how much energy is required versus how much is available. The trail is not as predictable as the road, so there are obstacles in efficiency; by creating a more substantial base through running economy and resilience through unbreakable form, an athlete can improve endurance and avoid injuries.

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Running Economy and Trail Running

In training, the goal is to make running at a higher or longer effort feel more effortless. Running Economy examines how much oxygen athletes use while running at a particular intensity. Continuing to look at the human body like a machine, oxygen is the fuel source, and a runner wants to be as sustainable as possible. With more efficient runners, less oxygen will be used for a more extended period, making them more efficient and fatiguing later. Using the body most efficiently creates less resistance and improves the overall economy of the athlete.

The issue arises on trails or in ultramarathons when obstacles or distances make the running economy less predictable. Dr. Sammie Lewis, a physical therapist who has studied biomedical engineering and teaches a biometrics course at the University of Colorado, explains that running economy might not be as good of an indicator of efficiency on the trail as it is on the roads. When you think about a flat trail or a fast 50k, it will matter, but when there is more transitioning from hiking or an obstacle that changes the pace, there will be less economy needed." Lewis says that running economy plays less of a role in most ultra distances than consistent fueling and strength. In a study conducted by the University of Colorado Sports Science program in 2021, looking at the changes in the walking-to-running transition at different hill grades, at a 10-12% grade, it becomes more efficient for a runner to switch to a practiced and efficient power-hike.

That is not to say that improving fitness has no role in longer distances. Focusing on low-output training can help a runner feel stronger and have more endurance on the trails. While running economy might not be a measurable device on technical or long runs, heart rate, and perceived effort are still good fitness indicators.

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Running Form for Trail Running

Inadequate running form can be a big reason for inefficient running or the potential for injury. The problem with evaluating and changing form is that minor adjustments can fix one problem but bring to light other weaknesses. Says Graboski, "The ideal form has a lot to do with the individual; there is no telling what the perfect biomedical form is for every person." Graboski, who works with the Veterans Association to design lower body prosthetics that mimic the human leg most accurately, does believe that there are adjustments that can be made that can reduce impact and help a runner experience more longevity in the sport.

How To Fix Running Form

Often, idiosyncrasies or imbalances in a running gait go unaltered, especially if the athlete is not Andrew Simmons, and Lydiard certified running coach who specializes in running form, says, "People often get their form evaluated because running is getting uncomfortable, or they keep finding themselves sidelined with injury." Simmons says that an obstacle in evaluating form on the trail is the lack of a continuously consistent surface. "Often, problems in the form are intensified at long distances or while running downhill, which is why trail runners need to get an evaluation," he says. There are some more common issues in running form that trail runners face, as well as productive ways to deal with the issue.

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Common Issues In Running Form

Hip Drop: Hip, or pelvic drops, occur when the leg is weighted (the standing phase of the stride.) It is caused by a lateral instability that causes the weight to shift medially into the leg that is off the ground. A hip struggling to stabilize will only be weakened by uneven terrain, where the entire body works to correct itself. Frequently, this issue is caused by weakness in the gluteus medius and hips, also called "dead butt syndrome," and can cause pain in the hips, knees, and ankles. It is best dealt with by strengthening and stretching the glutes and hips

Cadence: The stride rate, or steps per minute, measured as cadence. In a perfect world, an athlete on a controlled surface (such as a road) would aim for each foot to hit the ground 85-95 times per minute, making an ideal range of 170-190 strides per minute (SPM.) Simmons explains, "The more time your foot is making contact with the ground, the more impact it is taking, and the more likely you are to get injured." A faster cadence means that the foot is spending less time on the earth and more time relieved from stress. Things get tricky when the terrain gets technical and hills are involved.

Obstacles, such as roots, rocks, or uneven trails, can prevent an otherwise perfect cadence. Lewis recommends improving foot speed through agility drills. "It can be helpful to use a latter or utilize jumping exercises to improve foot speed and foot and ankle strength," she says.

The University of Colorado Study from 2021 that looked at trail running economy determined that a fairly consistent cadence can be held up until approximately 10% grade, after which a more focused hike will be more efficient. Downhills, however, present more of an adjustment from the body's natural inclination. "We tend to want to lean back and stride out," explains Lewis, "but we should try to move our body forward and shorten the stride." By adjusting form in this way, it will put less impact on the legs and give the runner more control.

Cross-over: If the body were to be divided perfectly down the middle, each foot would land on its respective side, but with cross-over, the landing pattern takes place while crossing the midline. This is often observed by the opposite side shoe connecting with the grounded ankle or foot during the swing phase and can lead to hip, knee, ankle, or back injuries. On single tracks, there is a required crossover, which can begin to feel like the norm. "It is not always an option to avoid a cross-over step," explains Lewis, "but you need to build up the resilience in your body to deal with it." This will involve lateral and single-leg strength and balance activities, ensuring that the ligaments in the body are strong.

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Posture: "When the body fatigues, it collapses in on itself," says Lewis. Working to build resilience and core and upper body strength can create a more upright posture that will promote airflow and endurance. Engaging the gluteous muscles can also relieve the hip flexors, which can cause issues with hinging or hunching at the waist.

Arm Swing: Ideally, with an arm swing, the elbows are at ninety degrees with a swing that does not cross or move away from the body, alternating with the swing of the legs. As poles are introduced, efficiency gets more important. The best use of poles is what is going to prevent the athlete from slowing or stumbling too much, though the best practice is to plant poles individually, with the opposite foot up to a thirty-degree incline, then double planting poles. Simmons also recommends keeping arms at 50-75% of a full extension while running with poles and avoiding a straight arm lock.

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Interventions To Fix Running Form

Biomechanics, while not a perfect science, can be adjusted and altered to improve efficiency with updated gear and changes in training.

Super shoes

Lightweight, high performance is growing in popularity, both on the road and the trail. With some shoes showing to improve running up to 4% on the road, performance could benefit from this intervention. Built with a carbon plate and super foam, the shoes are resilient and compliant; according to Graboski, who has helped work on some projects involving the shoes and relating them to her work with prosthetics, "they absorb impact without losing any additional energy," she says.

Strength and Engagement

Strength training has been shown to help both with improving running form as well as running economy. With asymmetry in the body, strength training can help engage both sides and discourage injury. Strong muscles are often tight, while weak muscles are over-stretched, so a combination of mobility and resistance can help create balance.

With Running economy, a 2019 study found resistance training can improve running economy anywhere from 2-8%. Specifically, the study indicated that higher weight with lower repetitions made the most impact.

According to Simmons, who has a series of strength training routines to help support correct running form, one of the biggest impacts a runner can make is adding a warm-up routine to their training. " I would rather see people do a dynamic warm-up and be mobile when they go out to run more than anything else. It won't make you faster neuromuscular, it will prime your brain to run efficiently." Running warm-ups have been shown to improve an athlete’s VO2 Max and improve muscular coordination.

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Road Running

Though road running might not be the most appealing place for a trail runner to train, improving speed and efficiency on a controllable surface can help improve biomechanics. "A lot of trail runners race in the summer and fall, so the winter can be a great time to get on the road and just focus on running economy and improving speed." Speed on the roads often translates to speed on the trails and can help trail runners feel better prepared when they move to their more specific race training.

If road running is feeling too daunting and form is still in need of improvement, Simmons recommends spending some time on a soft, flat surface after a training run. "Just practicing good form on a soccer field can make changes. If done barefoot, you can get more in tune with your body and start understanding what good form feels like." Simmons adds that one day or week of practicing does not make changes; it has to be a task that an athlete is present and persistent with, best done during the off-season.

There is still room for understanding in biomechanics for trail runners. That said, efficiency can be improved through improving form and running economy, creating more longevity and health in the sport.

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