I think people underestimate the extreme scientific sexiness of downhill running. When I started coaching, I used to think that downhills were a secondary consideration, something to focus on only after checking all of the other boxes. Now, it’s a pillar of how I think about success in the sport.
I’m going to start this article with some controversially confident statements. Time to bring the hottest heat.
Give me a track 5K star to coach, and I’ll show you a climbing monster in anywhere from 2 days to 2 weeks, depending on their biomechanics. The fastest runners will usually be the best climbers, with some exceptions that can usually be explained by lack of practice at wildly steep grades for a fast runner, or athletes who aren’t super fast who have incredibly high VO2 maxes (often coming from other sports like nordic skiing). A Vertical K race is some mix of a running economy test and a VO2 max test.
Give me a fast road marathoner, and I’ll show you an athlete that can excel in longer, non-mountainous ultras due to their aerobic and metabolic efficiency. That ability to push output around aerobic threshold as high as possible translates well to almost all distances above a couple hours. This one might take a bit longer, or it can be an instant crossover, depending on physiology.
But give me a beast from the track or road squad, and I have no freaking clue how their bodies will respond to repeated downhills on the trails. The form is hard to learn, the muscles contract in different ways, and there is uncertainty about how adaptations accumulate over time. During repeated downhill bouts, physiology gets thrown into the wood chipper. Sometimes, it can take months or years to build up the physiological resilience and biomechanics to excel.
What the heck is happening?
An incredible webinar on July 7 hosted by world-famous researchers Guillame Millet, Frederic Sabater Pastor, and Thibault Besson aimed to provide some answers about how to train for the difficulty of downhill running, gathering four of the world’s top scientists. I was also invited to give a coach’s presentation at the end.
Given how much I admire the organizers and panelists, it was a bit like one of those dreams where you show up to your final exam and you forgot to wear pants. Fortunately, it was a remote presentation, so pants were optional.
I learned so much in the webinar, and I want to share some of the takeaways with you all! This is such a sexy topic because we generally know what is happening to the body on downhills, but we don’t actually have agreement on how to train for it. That offset is an immense opportunity for every athlete and coach to learn the science and develop solutions that work for them.
Uphills reward speed and running economy development, until the grades get very steep. Endurance is endurance, with some small variations for very long events. But downhills can take what seems like perfect training, with what seems like perfect physiology, and leave you holding a trash bag of wood chips. I became a better coach in two hours on this webinar, and I’ll try to distill it here, but watch the whole thing to learn from the best.
Lesson One: The repeated bout effect can lead to rapid adaptations.
Arash Khassetarash reviewed how the repeated bout effect leads to astonishing adaptations to downhill running in a short period (starting at 3:40). As a primer, during downhill running, muscles undergo eccentric muscle contractions that can cause mechanical breakdown, peripheral fatigue, and central (nervous system) fatigue. As stated by a 2016 review in the European Journal of Applied Physiology: “Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers.” Downhills can turn legs into hamburger meat.
The presentation showed that these inflammation and breakdown processes can lead to adaptations of the muscle-tendon complex and the neuromuscular system. His 2022 study in the European Journal of Sports Science had athletes conduct 2 x 30 minute downhill runs 3 weeks apart in the lab. The second bout resulted in significantly less neuromuscular fatigue (measured as maximum voluntary contractions) and less quadricep pain. Just one session led to major adaptations!
Fascinatingly, biomechanics changed due to the repeated bout effect, too. In the first session, over the course of 30 minutes, ground contact time increased massively, while flight time decreased. Both of those intra-session changes were less pronounced on the second bout. There was attenuated strength loss due to better preservation of neural drive, along with better preservation of biomechanics due to increased leg stiffness (likely due to less muscle damage).
The big lesson here: these adaptations can happen shockingly fast, touching on everything from form to muscle strength to the nervous system. WOW! In coaching, I will try to keep athletes reinforcing these background adaptations as close to year-round as possible, with the 3-week timeline as a general guide for bigger stimuli outside of specific training.
Lesson Two: Field studies of downhill running show the super cool reasons why different athletes respond in different ways.
Marlene Giandolini is a sports scientist for Salomon, which has to be one of the coolest jobs on Earth. And that makes sense because she is a total badass. Her presentation (starting at 23:00) included some golden pieces of wisdom, and mostly from field studies that had athletes run down actual mountains!
For context, a 2007 study in the Journal of Sport Sciences found that a downhill running bout reduces subsequent running economy on level ground by 7%, with a 21% loss in knee extensor strength. Those are huge changes, and that was just from 30 minutes of downhill running! Now imagine what happens over the course of an ultra, when an athlete can feel like they pace well and still everything goes to shit and it gets impossible to run much at all.
Buffering that fatigue is not just about doing enough downhill running. Dr. Giandolini’s research pointed in some directions I have never written about. Her 2017 study in the Scandinavian Journal of Medicine and Science in Sports showed that foot strike pattern variability was associated with reduced neuromuscular fatigue and smaller performance reductions after downhill running bouts. In addition, a 2019 study in the European Journal of Sport Sciences showed that shoes with very low stack heights or very high heel-to-toe drops may correspond with worse downhill running. And a 2018 study in Frontiers of Physiology found that high-pressure compression gear ”was associated with beneficial effects on soft-tissue vibrations, acute and delayed neuromuscular function, and perceived muscle soreness.” On top of all of that, cognitive skills and risk-taking mentality can correspond with better downhills.
We generally know what is happening to the body on downhills, but we don’t actually have agreement on how to train for it. That offset is an immense opportunity for every athlete and coach to learn the science and develop solutions that work for them.
For downhill running, speed and practice matter, but there are plenty of other variables that can influence the process of performance and recovery too. In coaching, I am going to think more about how to encourage athletes to be flexible and loose with their downhill forms depending on the specific demands of the terrain, while recommending the right shoes, embracing a free-spirited and joyous outlook toward risk-taking, and getting those Euro-style compression shorts to move into the US trail scene. Prepare your thighs for a spandex embrace!
Lesson Three: Runnable downhills have different considerations than steep downhills.
Wouter Hoogkamer was the next speaker (starting at 51:00), talking about how pacing changes on runnable downhills. Now, I understand that these names might not mean much to you if you aren’t in this field, but I was this close to asking for their autographs (on my quadriceps, of course, to provide downhill superpowers).
I have admired Wouter’s work for a long time, so it was extra fun to get to see him present. A 2002 study in the Journal of Applied Physiology laid out the problem: the cost of running (energy it takes to go a given pace) can be very different as grades change. However, there is limited data on how those costs change at smaller grade changes between 0 and 5% downhills.
A 2020 study in the Journal of Sports Sciences used more refined calculations to help understand the quest for the sub-2 hour marathon. But my favorite part of the presentation was hearing about a soon-to-be-published study that aimed to quantify the metabolic rate while running downhill at moderate slopes between 0 and 5%. Across the study, the cost of running was reduced by 3.2% to 5.2% per 1% grade downhill.
In other words, to maintain the same metabolic rate, you need to go significantly faster on slight downs. This relationship (and the equation derived from this 2019 study in Frontiers of Physiology) will give me new coaching tools to help quantify what I mean by aiming for “purposeful flow” on downhills, particularly on long runs. It doesn’t mean you increase effort, it means you maintain effort at a faster pace, in order to prevent downhills from getting slower over time.
Lesson Four: Downhill performance stresses different parts of physiology, and knowing how those differences can help anyone improve.
The final scientific presentation was from Marcel Lemire, on the physiological factors that go into downhill performance. I often say something along the lines of “speed is speed.” He helped illuminate when that simple statement breaks down, and how those cracks can be filled with smart training.
A 2021 study in the Journal of Science and Medicine in Sport involved 10 highly-trained athletes doing an uphill and downhill 5k time trial, with physiological tests before, during, and after. That led to my favorite figure of all time (1:16:14). Yes, I’m going to print it and hang it up above the bed that my co-coach Megan and I share. It’ll get us in the mood for performance.
The figure details what variables determine uphill and downhill performance. Only one variable overlapped: velocity at VO2 max. This is the classic metric for “running economy,” showing yet again that running economy matters in trail running.
But that needs to be interpreted together with some other fascinating findings. For only uphill running, velocity at VT2 was important, usually corresponding to what we traditionally call lactate threshold, or ~1-hour effort. And for only downhill running, velocity at VT1 was important, usually corresponding to an effort an athlete could hold for a couple hours. Why would speed/vVO2 matter for both ups and downs, but tempo matter more for ups, and aerobic endurance matter more for downs?
While the exact reason is uncertain (and the results need to be repeated), my guess is that the ability to clear lactate is extremely important on uphills, when every little respite in the trail necessitates recovery, and the entire spectrum of high-end aerobic capacity matters. Specific longer-distance running endurance (vVT1) is less important because there is reduced impact, possibly explaining how skiers who wouldn’t run fast marathons can excel on uphill time trials. Meanwhile, downhills involve higher demands related to impact, so athletes need to have more miles and experience in their legs, with vVT1 being a proxy for that. That’s all conjecture though, based on coaching biases.
On top of those findings, on downhills, relative lower limb maximal strength and musculo-tendon stiffness mattered–likely because you need to be strong enough to absorb that impact and transmit the power back. General strength and stiffness might matter less on ups, when VO2 max and specific strength are more relevant. However, these results might be different at a different grade.
Bonus: Don’t get excessively stoked.
My presentation was supposed to be 12 minutes (starting at 1:31:30), and I’m now realizing that it was about two times longer than that. Just say no to tantric powerpoints.
One of the most exciting things about this sport is seeing how science and training theory interact over time. Trail running is wild because physiology is pushed to its absolute limits. And at the limits, we can find answers about what makes us all tick, far off the trails. I can’t wait to see what scientists and researchers learn next.
David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and you can find more of their work (AND PLAY) on their Patreon page starting at $5 a month.