This article originally appeared on Trail Runner
I absolutely love "longitudinal case studies" in exercise physiology. Usually, these types of studies gather a ton of information on training practices across years without trying to influence those practices, thus determining how real-world approaches translate to outcomes over time.
Because traditional control studies have difficulty measuring long-term interventions and isolating variables over years, there can sometimes feel like there is a chasm between training studies and training theory. Longitudinal case studies help bring the two together, applying rigorous data gathering and analysis to a whole boatload of variables to help determine what actually drives elite performance, within the context of the field more generally.
And today, we have a whopper of a longitudinal case study that was just published in the Frontiers of Physiology journal–one world-class male cross-country skier's training and racing data over ten years! What makes this study extra titillating is that it included two seasons of a steep performance decline relative to expectations, followed by a return to world-class levels. What caused the decline? And the rebound? Those are the questions the study sought to answer, and it could have major implications for how we think about training and adaptation across a career of pushing it to the limits.
Cross-country skiing is the frontier of applied exercise science for two reasons (see this article from last year). First, studies are being published constantly on elite training practices, which is much rarer in running. For example, a 2021 study in the Frontiers of Sports and Active Living journal analyzed the training of 12 world-class male skiers during their best seasons, finding that the athletes averaged around 800 annual hours of endurance training, with 88.7% easy, 6.4% moderate, and 4.8% harder. A 2017 case study in Frontiers of Physiology that is similar to the one we are looking at today examined the training of the best female cross-country skier ever, finding 849 hours of annual endurance training, with 92.3% easy, 2.9% moderate, and 4.8% harder. Cross-country skiers let physiologists into their training logs and camps, and a wealth of data is made public.
Second, cross-country skiing is–and this is a technical term–hard as balls. A 2015 review article in the Scandinavian Journal of Medicine and Science in Sports describes the sport as one of the most demanding activities humanly possible, combining upper and lower-body effort in a way that strains the aerobic system to its absolute limit. "Over the years," the authors say, "this unique sport has helped physiologists gain novel insights into the limits of human performance and regulatory capacity." Honestly, that seems like a lot of innuendo to indicate that it really hurts and kinda sucks, but to each their own.
The study we are looking at today built off the voluminous literature in two important ways: it provided a longitudinal approach that indicates how training changed to reach world-class levels, and it described potential pitfalls athletes face when pushing their bodies to the training limits.
Methods and Results
The methods were simple (or as simple as 10 years of detailed training analysis can be). A 31-year-old Norwegian male athlete provided training data that included heart rate and blood lactate measurements, along with multiple interviews with the athlete and coaches to gather non-training data.
Over 10 seasons, the athlete increased endurance training volume from 691 hours a year to 926 hours a year, consisting of relatively similar intensity distribution over time (~91-93% easy, ~4-5% moderate, and ~3-4% harder). Strength training stayed constant, and speed training increased by 5 times (from 3 hours per year to 20 hours per year) as the athlete progressed to world-class levels.
But then the athlete hit the wall. The authors laid it out: "The participant started to experience periods of glycogen depletion during training and competitions, as well as a feeling of low energy availability, particularly during the nights. This was coincided by increased CHO oxidation during rest."
Now is when things get really interesting. When the athlete started underperforming, training volume and general intensity approach didn't change, but the specific training and nutritional methods did. While it's impossible in a case study to be certain that Intervention A caused Outcome B, we can gain confidence if it overlaps with our understanding of exercise physiology and training theory generally. And here, the overlap was striking.
Let's outline the interventions that coincided with underperformance:
Training with low carbohydrate availability during most easy sessions
Performing AM sessions in a fasted state
Including easy activities longer than 4 hours in a fasted state
Days with multiple moderate/threshold workouts on a single day
"A lack of systematic technique training and follow-up by coaches on a day-to-day basis outside training camps"
After multiple underperforming seasons, the athlete and coaches did a holistic intervention to reverse the damage. Intensity distribution was similar, but endurance training volume increased (due to not having to take long breaks with fatigue) and there was a higher periodization index (a greater spread between hard weeks and easier weeks in 3-week cycles), along with more fueling during and around training sessions.
Excess Stress During Underperformance
WOW! That is some fun data to dig into. The first very cool finding has nothing to do with the years of underperformance. Instead, it's the sheer volume of training the athlete completed over time to reach a world class level in the first place! Interestingly, the increase almost all came from higher volumes of low-intensity specific endurance training, with almost no change in supplementary work like strength. That backs up the findings of other studies–there is no substitute for aerobic base. However, that base was combined with speed development. Even though pure speed work only increased by 17 hours (from 3 to 20 hours per year), that change helped the athlete "close the gap between the sport-specific demands and the participant's limitation in 'high-speed capacities.'" The aerobic system is paramount, but building up aerobic base is best when it's done in a speed context.
The underperformance window coinciding with underfueling makes total sense to anyone who has read the literature on low energy availability and within-day deficits. As the authors say, the interventions "included a rather 'extreme' regime of training with low CHO availability and days with two MIT sessions without sufficient intensity control." Fasted training may have some minor benefits for some male athletes given how it may improve fat oxidation (with possible improvements in some adaptation markers as well), but in athletes that are doing high training volumes, fat oxidation will already be relatively optimized. For female athletes, the pitfalls of fasted training are even worse, but without the potential benefits, so it should usually be avoided at all costs. Any small benefits a male athlete may be able to achieve with fasted training is likely countered by an absolute hormonal shitstorm that may be unleashed from excessive deficits. Even if the athlete fuels enough the rest of the day, the depletion likely destroys adaptation capacities, particularly at the world-class level where every sliver of a percent matters.
And that was backed up in how training unfolded during the underperforming window. The authors say: "The micro-cycle load structures during the seasons of underperformance were characterized by accumulation of high stress-loads until 'forced' easy-load cycles were needed." The old saying applies: Listen to the body when it whispers so you don't have to hear it when it screams. Those screams of forced rest probably coincided with less capacity to adapt to the workload, which starts as small signals in performance metrics before it becomes large signals of injury, illness, or burnout.
The complex part of the equation is that this situation may not be a simple diagnosis of RED-S or overtraining syndrome. In fact, "the participant was not diagnosed with RED-S and blood markers of RED-S were considered within normal ranges." However, the stress levels of the training program seemed too high to buffer any excess stress from inadequate fueling, even if that depletion fell short of clinical diagnosis.
That's the most important realization that all athletes need to have. Hard training is HARD, filling up the stress pot to the brim. Inadequate fueling puts two key ingredients into a shit stew: adding stress to the pot, and shrinking the pot. Put it together, and hard training without big fueling eventually leaves the whole house covered in shit.
Stress Management in Training
Perhaps the athlete could have weathered the storm of occasional underfueling and new training methods if they weren't already pushing their body to world-class levels. "However," the authors say, "the introduction of such methods in a training process already characterized by high stress-loads without careful periodization, monitoring, and intensity control are likely contributing factors." Those new methods included double-threshold workouts (a la the Norwegian training approach), but those types of workouts without tons of carbohydrates can become ticking time bombs for athletic growth.
In bouncing back, the athlete started eating more during and around training, consisting of 8-12 grams per kilogram a day, depending on training levels. That is A LOT of carbs, akin to some of the studies on runners in the middle of pre-ultra carb loading. The lesson is that pushing the body to the stress max is often indicative of a need to load up on carbs almost like you're approaching race day.
The athlete also took out the double-threshold sessions, had more coach feedback, and started periodizing training more intentionally. Whereas before it was push-push-push until the body gave a major signal of a setback, it turned into a micro-cycle periodization of easy, moderate, and heavy-load weeks (easy weeks still totaled 15 hours, so it was a question of controlling the extremes). In addition, the athlete was more open to changes after the underperformance, especially given the increased presence of the coach. As the authors say, "adaptations to training are not solely dependent on the physiological/mechanical stimulus, but also associated psycho-emotional considerations such as the athletes understanding and belief in the training plan, as well as a sense of purpose and 'ownership' of the training process."
A 2020 study in the International Journal of Sports Physiology and Performance did a similar analysis of the world's best female skier after a period of underperformance (the same athlete from the 2017 study cited above), finding that a holistic approach focused on whole-life stress management was needed, preventing the push-push-push cycles that can cause regression.
The authors had four practical pieces of wisdom that I think are relevant to all athletes. First, treat training and underperformance with a holistic approach, with an understanding of the physical and mental contexts, a finding echoed by the 2020 study. Second, when training hard, periodize weekly cycles to avoid excessively pushing into stress holes where the body stops responding. Third, monitor the body to detect adaptations or maladaptations (with or without a coach).
But this final one is where I really want you to pay attention. The authors say: "A training philosophy based on mitigating risks (reducing the risk-benefit ratio) by performing the majority of training sessions with 'control' seems beneficial." The body adapts when there is stress room to spare, since filling the stress pot to the maximum almost always results in it boiling over, even if that process takes a few years.
If we had unlimited resources and could do daily blood tests or other physiological monitoring, we'd probably see the pot boiling over before it happens. In the real world, though, athletes need to make decisions that allow them to keep stacking little bricks in a really big wall, without taking a sledgehammer to the wall through acute overstress, or weakening the soil the wall rests on through chronic overstress. That includes eating enough to fuel the work and avoiding excessive intensity within individual sessions and across training blocks. I love this mic drop line from the study: "This may be important not only for underperforming endurance athletes, but endurance athletes in general." The hardest part is that many motivated athletes respond to underperformance by thinking they are not doing enough work, when the reverse is often true.
Train big and train lots and believe in the process most of all, because that's what it takes to see what the body can accomplish. But also train to feel good, because long-term adaptation relies on a healthy stress balance. The body adapts in the empty spaces, especially when those empty spaces are full of food.
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 they answer training questions in a bonus podcast and newsletter on their Patreon page starting at $5 a month.
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