Understanding Allostatic Load in Athletes: The Unwanted Energy Thief

In the high-stakes world of competitive sports, the pursuit of peak performance often comes at a cost. A cost that isn't always visible. Imagine a professional cyclist meticulously preparing for the Tour de France, ticking every box from executing their training, weighing out every single food they eat, sleeping 8h per night and managing their public persona. However, athletes are not robots. External or internal expectations, fear of failure, conflicts in personal relationships, the high training demands, negative press or other stressors can derail even the most finely-tuned athlete.
This article delves into the concept of allostatic load – a hidden energy thief that can undermine both health and performance. We will explore how physical and psychological stressors interact, how they can lead to conditions like Unexplained Underperformance Syndrome (UUPS), and why it is crucial not to underestimate mental stress. By understanding how much mental “stress” can cost us from an energy-perspective, we can develop better awareness for unwanted energy leaks, mitigate its impact, and pave the way not just for optimal performance but more sustainable athletic careers.

Allostasis, Allostatic Load and the Stress-Disease Cascade

We all operate within a finite energy budget. In endurance sports like cycling, it is fairly straightforward to quantify the energy burned through physical exertion (exercise energy expenditure). However, the energy drain from psychological and social stressors is much more elusive and challenging to measure.

Humans have an innate ability to anticipate, regulate and adapt to stress – a process known as allostasis – which helps maintain stability and energy balance. This adaptive process is highly efficient but also energy-intensive, as the brain consumes significant resources to manage stress responses^[i].

When we push our physiological and psychological limits for too long and stress becomes chronic, the body’s allostatic systems – such as the hypothalamic-pituary-adrenal (HPA) axis, sympathetic nervous system, and various metabolic pathways – are constantly activated. In other words, the temporary allostatic responses of the body, which are essential for survival and also help us to improve performance, shift into persistent allostatic states.

The constant activation of allostatic states incurs additional energetic costs and can disrupt the balance between energy production and consumption within cells and the organism. This disruption can for instance occur through permanent cellular and physiological recalibrations such as hyperglycaemia, increased blood lipids and elevated levels of circulating stress mediators. Over time, these prolonged states of stress and increased energy consumption can lead to a state known as allostatic load.

As allostatic load persists over time, the body continues to make significant efforts to cope, but these (mal-)adaptations can result in serious health issues. For example, arteries may stiffen to manage high blood pressure, hormone receptors may become less responsive to prevent overstimulation, and the brain's structure and wiring may change due to chronic stress.

This cascade of stress-related damage, from initially adaptive (and wanted) allostatic responses to maladaptive states, can eventually cause communication breakdowns within the body's systems. These breakdowns not only impair (and possibly shut down) performance and recovery, but also pose significant health risks through allostatic overload. This relentless energy demand can overwhelm the body’s systems, leading to detrimental effects such as cognitive decline, hypermetabolism, and potentially accelerated aging, along with an increased risk of chronic disease^[ii].

Figure 1: The allostatic load model explains how stress can lead to disease and accelerated aging. Stressors, whether real or perceived, trigger an energy-dependent process that progresses from adaptive allostasis to allostatic load, and eventually to allostatic overload, along with an increasing disease risk. The body's physiological network, involving constant communication between cells, tissues, and organs, is disrupted by stress, leading to dysfunction and impaired system communication. These changes, illustrated by altered biomarkers, eventually manifest as clinical symptoms. This model is adapted from McEwen's allostatic load time-course^[iii]. Figure taken from Bobba-Alves et al ^[ii].

The Link between Health and Performance

Chronic disease doesn’t develop suddenly, but early signs of allostatic load – such as declining performance, chronic fatigue, or frequent injuries and illnesses – can affect even the most dedicated athletes. This connection underscores the intricate relationship between health and performance. Striving for peak performance does not always align with optimal health, yet physical and mental well-being are essential foundations for sustained success in endurance training and performance^[1].

Despite their relevance, terms like allostasis, allostatic systems and allostatic load are not commonly discussed in sports and exercise physiology, even though they are closely related to how athletes adapt to training. What is it about the allostatic load’s primary mediators (e.g., stress hormones, cytokines, metabolites) that disrupt health-sustaining biological and physiological functions? When does adaptive allostasis become allostatic load and overload? Although researching these concepts is challenging, it is crucial to explore and find ways to monitor, understand and manage those concepts and their consequences for athletes effectively.

Expectation versus Reality: The Dual Burden of Physical and Psychological Stress in Athletes

Training stress is a normal part of an athlete’s life. But mental stress such as competition anxiety, media scrutiny, or personal issues can significantly add to an athlete’s overall stress level – and this too costs energy!  The problem is that we don’t have psychological markers (analogous to e.g., physiological thresholds) or scales such as psychological intensity zones to measure the intensity and type of stress or determine how much energy it really costs.

The theoretical framework of the “free energy principle”^([iv]) states that dynamic physical systems pursue paths of “least surprise”^[2]. Thereby, stress can be understood as the brain’s attempt to minimize "free energy," which is a balance between accuracy—our ability to predict sensations—and complexity—the allostatic resources needed to make these predictions. Stress arises when there is a mismatch between our expectations and reality, whether due to unexpected performance outcomes, disruptions in routine, interpersonal conflicts or other unforeseen events.

For example, an athlete might expect to perform at a certain level and experiences stress when that expectation isn't met. Even minor disruptions, like having dinner an hour later than usual, can generate stress because they challenge the brain’s predictions. This stress reflects the brain's effort to reconcile these discrepancies, which increases energy consumption and affects overall performance. Allostasis, hence is inherently anticipatory, preparing us for upcoming challenges—whether they materialize or not.

The human mind is a powerful source of unnecessary stress, what we might call "wasteful allostasis." Overthinking is a prime example of such an "energy leak," where mental stress can strain the body similarly to continuous high energy expenditures from intense training. This happens when we start losing our predictive grip on what’s happening around us: we lose our “normal”. For instance, when we’re not performing optimally over a long period or have skewed expectations and ambitions. Our mind, in its attempt to reconcile this disconnect, searches for the smallest evidence to support its internal model, often leading to overthinking and worry. This triggers energy-draining stress responses that don’t contribute to physical adaptation. Instead, they deplete our energy reserves, hinder recovery, and ultimately limit our ability to perform at our best.

In Summer 2023 I went through a period of “Unexplained” Underperformance. A topic for a different blog post ;-)

When non-training-related stressors take up too much energy, athletes may develop Unexplained Underperformance Syndrome (UUPS), where they suddenly start underperforming in training or competition without any clear physical cause. UUPS often arises not from training overload alone but from the cumulative effect of non-training stressors, which are frequently overlooked in athlete monitoring systems. To prevent this, it is crucial to check in with athletes on a regular basis and integrate the monitoring of external stressors (e.g. travel, exams, finances) and psychological assessments (e.g., POMS)^[v] into holistic athlete management systems, allowing for proactive interventions and ensuring training continuity.

At the core of this issue is the fundamental role of energy in the body’s overall functioning and ability to adapt to stressors or challenges. Being mindful where your energy “goes” is key to avoid performance declines like UUPS. Thereby, the challenge lies in balancing stress: either by ensuring your expectations are consistently met – a perfectionist approach that demands immense, if not impossible, control over your environment – or by becoming more flexible and less rigid in your expectations. This flexibility lowers the brain’s energy demands, preventing it from overwhelming your system and facilitating more sustainable performance.

The Mystery of Maximal Sustainable Energy Expenditure

Professional endurance athletes are known to train many hours, which is often positively correlated with performance. High training volumes consequently lead to high energy expenditures. It has been speculated that the maximal sustainable energy expenditure is approximately 2.5 x the basal metabolic rate^[vi], a constraint imposed by our ability to transform energy^[vii]. However, some athletes and coaches have reported consistently higher workloads and significantly higher energy intakes (especially carbohydrates) than previously known.

In a complex system like the human body, we rely on the adaptability of our allostatic systems to make sure that we stay in “balance” even under extreme circumstances. Adequate energy intakes might allow these athletes to become resilient to the higher demands (workloads), either by 1) metabolic compensation (efficiency-induced resilience)^[3], allocating energy to fuel adaptive processes, or 2) by increasing the total energy budget. At the moment, this is still pretty much a blackbox and might even vary depending on the individual case.

In any case, the ability to sustain a much higher workload has certainly contributed to significant performance improvements in recent years. Nevertheless, we have yet to gain a comprehensible understanding of the “costs” of constantly altered regulatory set-points (e.g., much higher energy budgets due to much higher energy intakes), but also the potential consequences of energy being allocated away from health- and longevity-promoting functions such as maintenance and repair or growth, reproduction and cognition.

Impact of nutrition and Hydration

Proper nutrition and hydration are essential not just to sustain high workloads but also for managing stress effectively. A balanced diet that provides the necessary macro- and micronutrients supports the body’s energy balance and recovery processes.

High training volumes lead to high energy expenditure, necessitating high energy intake. A better understanding of nutritional strategies, such as optimizing carbohydrate intake (daily, during training and competition), has played a significant role in enhancing performance and increasing load tolerance in recent years^[viii]. However, it is important to recognize that simply consuming more and more carbohydrates does not enable athletes to train infinitely more. There will come a point when “more” doesn’t give you any additional performance benefit, as other factors like digestion, absorption or the feeling of fullness might become a constraint.

It is also crucial to remember that nutrient intake is not the same as nutrient uptake. The body needs to process food, and the more you train, the less time there is for digestion and absorption. However, adaptations to long-term exercise can make our bodies more biochemically efficient. This means, we can probably absorb more of the nutrients we take in and use fuel more efficiently, such as utilizing more fat at lower intensities while maintaining the ability to oxidize carbs at a high rate when needed.

Adequate hydration is equally important for maintaining optimal physiological functions. Additionally, small molecules like antioxidants^[ix] and adaptogens^[x] can help mitigate oxidative stress and may enhance the body's resilience to stress, although too high dosage may prevent performance-enhancing and health promoting adaptations^[xi].

Given the variability in daily energy expenditure and the challenge of estimating it precisely, it is vital to also listen to the body’s signals of energy deficiency (or surplus) and not fighting against your “natural self”. Being aware of your natural physique, the type of athlete you are and your nutritional habits, can help you understand your tendencies and guide your combined approach to training and nutrition. Hereby, athletes can also benefit from working with nutritionists to create individualized plans that cater to their specific needs, considering their training demands, natural physique, past and current eating behaviors and overall lifestyle. Certainly however, adequate nutritional input and high quality foods can be a game changer and enhance the capacity to handle more stress (mental and physical) and are therefore an important factor in performance improvement and sustainability.

The Role of Technology in Monitoring Allostatic Load

Advances in wearable technology have revolutionized the way athletes monitor their physiological states. Devices that measure resting heart rate, heart rate variability, breathing rates and sleep quality enable athletes and coaches to make more informed decisions about training and recovery. Moreover, the integration of big data and machine learning increasingly allows to get predictive analytics, potentially helping to identify early signs of allostatic overload or underperformance, enabling proactive stress management and preventing long-term detrimental effects.

However, we are still lacking direct measurements that indicate overall stress load. While a lot of wearable devices use algorithms to predict “stress levels” using a variety of data inputs, these are not direct measurements. You can’t prick your finger or spit into a tube and get a concentration of your stress levels – yet. But even if we could, for instance, measure biomarkers like hormones in real-time, they are most likely only facilitators and not the reason of chronic effects.

Perhaps in the (near) future we will be able to measure stress-induced (e.g., neurotransmitter-related) brain changes, gain real-time insight on neurogenesis or neurodegeneration, or measure cellular energy fluxes which will provide a more direct understanding? Methodologies like electroencephalography (EEG) have already been used to suggest that exhaustive exercise temporarily reduces brain network efficiency and using EEG for resting state network assessments could be one way to facilitate the evaluation of readiness and efficiency of the central nervous system in different training situations.^[xii] However, it remains speculation whether these assessments are on the same temporal scale than our thoughts, perceptions and feelings, or whether we can only ever measure “delayed allostatic load”.

Cultural Factors and Gender Differences

Cultural and gender differences can also significantly influence how athletes experience and manage stress. Some athletes might naturally have more relaxed dispositions, which can buffer the impact of stress, while others have to be very conscious that the energy they spend on mental stress doesn’t cause physical shutdowns.

Additionally, hormonal variations can influence stress responses and recovery, with women potentially experiencing different stress impacts (and energy modulations) due to menstrual cycles. Social expectations and pressures can also vary widely across cultures, affecting how athletes perceive and cope with stress. With the current use of smartphones and social media, it is also becoming increasingly important that athletes are taught how to properly “switch off” from an early age. Hereby, educational programs that teach (young) athletes about stress management and recovery can be beneficial, helping them to develop strategies to balance their training with other life demands.

Coping Strategies to manage Allostatic Load

From an evolutionary standpoint, we’re wired to seek out things that conserve or replenish our energy, like enjoyable activities or comfortable environments, and to avoid situations that drain it, such as uncomfortable conditions or stressful tasks. This instinct helps us minimize the energetic costs of life. To manage stress, we need to develop an awareness of our most prevalent stress sources. Also, where do we want to and where do we actually spend our energy? In other words: Use your energy wisely, channel it into activities that you enjoy, that enhance your capacity to tolerate stress or promote recovery. On the flipside, don’t try to be perfect (nobody is!), stay relaxed and maybe lower your expectations a little bit to avoid unnecessary stress. This approach allows us to reduce our overall stress levels and be a much more pleasant and healthy person, while improving our adaptability and resilience.

Other useful strategies to manage allostatic load include:

• Low-stress physical activity: Engaging in activities like walking or hiking in nature, technical/skill sessions, or light gym and plyometric sessions without focusing too much on data or metrics can help to stay active while reducing stress.

• Support Systems and Human connection: Seeking support from a sports psychologist, coaches, and family can help manage stress. Good coaches are able to monitor and manage athletes' stress and recovery. Social connections can help to distract yourself and remind you that there are also other things in life.

• Mindfulness and Relaxation Techniques: Practicing mindfulness, meditation, and biofeedback techniques can reduce anxiety levels.

• Balanced Lifestyle: Ensuring adequate rest, high-quality sleep, natural light exposure, good nutrition, and time for friends, joyful activities and relaxation to maintain overall well-being.

• Goal Setting: Setting realistic, achievable goals to maintain motivation and a sense of accomplishment.

• Positive Self-Talk: Encouraging a positive mindset and focusing on strengths and past successes.

Conclusion

Understanding and managing allostatic load is not just a matter of optimizing performance in the short term – it is about safeguarding an athlete's long-term health and career longevity. While the physical demands of training are meticulously calculated, the psychological and social stressors often go unmeasured and unmanaged, and can quietly erode an athlete's capacity to perform and recover. These stressors, when left unmanaged, can lead to unexplained underperformance and even chronic health issues, undermining an athlete’s career and overall well-being.

By integrating strategies that address both the mind and body athletes can build a robust defense against the cumulative effects of allostatic load. Furthermore, in the future we may develop a better ability to predict and monitor (hidden) stressors through advanced biomarkers and wearable technology, allowing for more immediate or proactive adjustments to training and recovery protocols.

Moreover, it is important to recognize – and better understand – the variability in how different athletes respond to stress. For instance, considering the influence of factors like genetic and epigenetic predispositions, the impact of traumatic experiences, and the complex interplay between physical, psychological and environmental stressors. Additionally, cultural differences and gender-specific stress responses may play significant roles. While scientific evidence on these factors is still lacking, experienced coaches may already have an intuitive grasp of these subtleties, allowing them to craft training programs that push the limits of human performance without compromising the athlete’s overall well-being.

If you have made it this far, it is clear that there is a thirst for case studies and practical evidence to support these concepts. Unfortunately, longitudinal studies in this area, extending beyond athletes’ careers are lacking – at least to my knowledge. Given the complexity and importance of this topic, I believe it warrants a thorough scientific exploration. If not through an experimental study perhaps in the form of a conceptual paper that synthesizes existing knowledge and sparks further discussion. I would be very interested to hear if I have missed any existing research, or if someone is interested in conducting such a study. I would be happy to help connect and support efforts to gather more insight on this important topic and I’m open to discuss any additional inputs or critics.

Thank you to Matěj Nekoranec, Øyvind Sandbakk, Trond Nystad and Benjamin Lain for constructive feedback and inputs to this article.

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^[1] A statement often emphasized by Stephen Seiler, for instance here: The Norwegian Mindful Talent Development Pyramid | NRW Kongress 2024

^[2] Wikipedia: Free Energy Principle

^[3] Not just metabolic efficiency, also biochemical and mechanical efficiency play a role.

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^[ii] Bobba-Alves N, Juster RP, Picard M. The energetic cost of allostasis and allostatic load. Psychoneuroendocrinology. 2022 Dec;146:105951. doi: 10.1016/j.psyneuen.2022.105951. Epub 2022 Oct 8. PMID: 36302295; PMCID: PMC10082134.

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^[iv] Friston, K. The free-energy principle: a unified brain theory?. Nat Rev Neurosci 11, 127–138 (2010). https://doi.org/10.1038/nrn2787

^[v]   Berger BG, Motl RW. Exercise and mood: A selective review and synthesis of research employing the profile of mood states. J Appl Sport Psychol. 2000;12(1):69–92.

^[vi] Thurber C, Dugas LR, Ocobock C, Carlson B, Speakman JR, Pontzer H. Extreme events reveal an alimentary limit on sustained maximal human energy expenditure. Sci Adv. 2019 Jun 5;5(6):eaaw0341. doi: 10.1126/sciadv.aaw0341. PMID: 31183404; PMCID: PMC6551185.

^[vii] Yang X, Heinemann M, Howard J, Huber G, Iyer-Biswas S, Le Treut G, Lynch M, Montooth KL, Needleman DJ, Pigolotti S, et al. , 2021. Physical bioenergetics: energy fluxes, budgets, and constraints in cells. Proc. Natl. Acad. Sci. USA 118.

^[viii] Thomas DT, Erdman KA, Burke LM. Position of the academy of nutrition and dietetics, dietitians of Canada, and the American college of sports medicine: nutrition and athletic performance. J Acad NutrDiet. 2016;116(3):501–528. doi:10.1016/j.jand.2015.12.006

^[ix] Clemente-Suárez VJ, Bustamante-Sanchez Á, Mielgo-Ayuso J, Martínez-Guardado I, Martín-Rodríguez A, Tornero-Aguilera JF. Antioxidants and Sports Performance. Nutrients. 2023 May 18;15(10):2371. doi: 10.3390/nu15102371. PMID: 37242253; PMCID: PMC10220679.

^[x] TrainingPeaks Article about Adaptogens for Athletes

^[xi] Li S, Fasipe B, Laher I. Potential harms of supplementation with high doses of antioxidants in athletes. J Exerc Sci Fit. 2022 Oct;20(4):269-275. doi: 10.1016/j.jesf.2022.06.001. Epub 2022 Jun 11. PMID: 35812825; PMCID: PMC9241084.

^[xii] Büchel D, Sandbakk Ø, Baumeister J. Exploring intensity-dependent modulations in EEG resting-state network efficiency induced by exercise. Eur J Appl Physiol. 2021 Sep;121(9):2423-2435. doi: 10.1007/s00421-021-04712-6. Epub 2021 May 18. PMID: 34003363; PMCID: PMC8357751.