In this episode, we take a deep dive with Manuel Sola Arjona — former professional cyclist, coach, and author of The Nature of Training — into how complexity science applies to endurance training. He discusses the human body as a complex system, an evolutionary perspective on training, and the dangers of reductionism, sharing his insights on RPE-based training, the importance of recovery, and the role of AI and big data. The central message is the importance of a holistic approach to training and learning to listen to your body's own signals.

1. Manuel Sola Arjona's Background and The Nature of Training

Manuel Sola Arjona started cycling competitively at age 14 and raced through every category, becoming a professional cyclist before transitioning into coaching. 🎓 He studied sports science at the University of Granada and pursued a master's in nutrition, devoting eighteen years as both athlete and coach to continuous learning and training. That passion led him to host the popular Spanish podcast Rendimiento Evolutivo and to write The Nature of Training, a book capturing his insights on training and performance.

1.1. The Meaning Behind the Title: Nature

Manuel explains that "Nature" in the title does not simply mean forests — it means everything that exists in the universe, a concept he likens to the Buddhist notion of style.

"When I say Nature, I don't just mean forests. I mean everything that exists in the universe. It's similar to the Buddhist concept of style. Complex systems are nested at many levels, and we are all interdependent — from molecules to cells, from organisms to communities, ecosystems, and planets. In the end, as the book says, there is one single complex system I call Nature."

He emphasizes that humans have long been studied as though separate from their environment, yet the same laws and properties that govern all systems apply to us as well. Understanding the laws of complexity, he argues, allows us to approach health far more effectively.

2. Complexity Science and the Dangers of Reductionism ⚠️

2.1. What Is Complexity Science?

Complexity science is an emerging field that fuses insights from many disciplines to study how specific behaviors and patterns emerge from systems made up of countless interacting parts. The word "complex" derives from the Latin complexus, meaning "intertwined" or "woven together," reflecting how the relationships within a system function as an integrated whole.

Manuel notes that thermodynamics can explain how a living system breaks down into dust, but cannot explain how dust becomes a living organism — and that understanding this transformation requires complexity science. The human body is arguably the most complex system of all, and adaptive complexity — a branch of complexity science — focuses on systems capable of adapting to their environment. A hurricane is a complex system but cannot adapt; humans, by contrast, can adjust and change their behavior in response to a wide range of influences.

"Thermodynamics can explain how a living system breaks down into dust, but it cannot explain how dust becomes a living organism. Understanding that transformation requires complexity science."

He describes how we have long tried to understand and improve the human body through isolated, reductionist approaches — like studying only one species of tree in order to understand how a forest works.

2.2. Reductionism in Endurance Sports

Reductionism is the scientific approach of breaking a complex system down into smaller, more manageable parts, solving each in isolation, and then attempting to understand the whole. This approach has achieved great success in technology, but it has clear limitations when applied to complex systems like human physiology or training.

Manuel warns that reductionism, when misapplied in training, can lead to false conclusions. Recommendations for athletes are often based on research that measures the effect of isolated variables far removed from real-world scenarios. Molecular physiology — proposing training methods solely because a specific protein is activated or a particular hormone level rises — is a prime example.

"I remember a study arguing that caffeine increases glycogen resynthesis rates and is therefore suitable after exercise. That is a reductionist approach, because the goal isn't simply to increase glycogen resynthesis — it's to recover faster. Focusing on a single parameter can degrade other parameters that matter for entering an anabolic state, such as sleep and rest."

We must understand that we are not merely mitochondria, dopamine, muscle mass, or blood-glucose spikes — we are beings in whom all these elements interact within our unique environments and personal histories. He also cautions that the concept of "marginal gains" can be misunderstood: improving one metric may sacrifice another, producing a net negative effect.

3. Properties of Complex Systems 🔄

Among the many properties of complex systems, Manuel places special emphasis on emergence. Emergence refers to the phenomenon whereby new properties appear at the system level that could not have been imagined from the behavior of individual parts alone.

• Emergence: Just as consciousness emerges from the electrochemical interactions of millions of neurons, cellular function arises from the combined action of organelles and proteins. These emergent properties result from synergies among the parts and therefore cannot be observed or predicted by studying each part in isolation.
  • Example: Pedaling technique, running form, and cadence. As the organism's state changes, cadence and technique may shift accordingly.
• Circular Causality: The entire system interacts in an endless loop. A change in a part changes the whole; a change in the whole changes the parts. There is no simple cause-and-effect in the body — one cause can produce many effects, and those effects become causes of still other effects. These mutual relationships keep the system in a state of dynamic stability.
• Nonlinear Behavior: There is no stable relationship between the size of a perturbation and the magnitude of its impact.
  • Example: An athlete can accumulate training load and microscopic muscle damage with no apparent decline in performance or injury. Muscles and the organism can maintain activity despite some damage through compensation and synergy, yet at a certain point that accumulated damage can exceed what the body can manage, resulting in injury or serious harm.
• Function Shaped by System Goals: A distinctive property of dynamic, flexible systems is that the system's goal determines its function. The system can modify its internal operations to achieve that goal.
  • Example: Cortisol levels and blood pressure look very different in a person who is relaxed and meditating versus one who is anxious and ready to run.

4. The Link Between Evolution and Training 🏃‍♀️💨

Manuel explains that organisms, including humans, were not designed by a creator but evolved through ecological and evolutionary processes to adapt to their environments. Our form and physiological function are driven by the necessities of survival, not intentional design.

"Organisms were not designed by a creator; they evolved through ecological and evolutionary processes to adapt to their environments. Our form and physiological function are governed by the necessities of survival, not intentional design."

In his book he argues that function is more important than form, and that by understanding the stimuli humans evolved to respond to, we can provide those stimuli without needing detailed knowledge of individual physiology. Hunter-gatherers needed no scientific research to strike the optimal balance of stress, rest, food, safety, and synchronization — their bodies naturally adapted to thrive in their environment.

Today, despite all our technological advances, we carry the same genes and physiology as our hunter-gatherer ancestors. Our bodies are optimized to respond well to these evolutionary stimuli. Humans are not particularly fast, strong, or agile compared to other animals, but we excel at endurance — especially in hot environments, thanks to our ability to sweat and our efficient upright posture, which minimizes exposure to solar radiation. This is precisely why low-intensity exercise over long durations was dominant in our evolution and why our bodies are so well adapted to it.

This evolutionary background explains why successful endurance athletes often train with large volumes of low-intensity work. It also highlights the growing importance of contextualized strength training when we consider our ancestors: the strength work they performed was explosive, involving natural movements — throwing, fighting, climbing, jumping, and sprinting. Sprinting demands maximal force output, making it a powerful stimulus. Manuel stresses that evolutionary stimuli should form the foundation of all training, conferring health benefits and remaining sustainable for life without causing injury or imbalance.

5. Manuel's Training Methodology 🧑‍🏫

Manuel defines his training approach as "a delicate balance between stimuli that keep the body healthy and stimuli that help improve performance in competitive sport." Focusing solely on general health may prevent athletes from achieving the standout results they aim for, while focusing too narrowly on specific performance can yield short-term gains but ultimately lead to imbalance, injury, or illness. 🤕

He moves away from traditional training models that emphasize intensity alone, believing instead in co-directed training between coach and athlete. The coach provides theoretical and practical knowledge of human physiology, the training process, and emotion-influenced decision-making; the athlete contributes insight into their own feelings, preferences, and motivation — and the synergy between the two should exceed the sum of their individual contributions.

"Good synergy is greater than the sum of both parties' contributions. The coach provides theoretical and practical knowledge of human physiology, the training process, and emotion-influenced decision-making. The athlete, in turn, provides insight into their own feelings, preferences, and motivation."

Because the training process is dynamic, it begins with the athlete's current state and sets short-, medium-, and long-term goals. The path to those goals is uncertain and requires adjustment along the way. He describes it as "dancing with the system," emphasizing that what works to improve performance today may not work tomorrow.

5.1. RPE-Based Training Prescription

Manuel explains that RPE (Rate of Perceived Exertion), sensations, and other evolutionary tools help athletes make the right decisions. The instincts to sense hunger, thirst, and fatigue, and to recognize emotions such as fear, anger, and sadness, helped our ancestors survive. He compares the perception of effort to an advanced processor that monitors stress data affecting the whole body in real time and weights it accordingly.

RPE is useful in training precisely because it is influenced by fatigue, mood, and stress. He warns, however, that over-relying on data from devices like Garmin can cause athletes to miss these subjective signals. Data may provide peace of mind, but it measures only part of the system within a margin of error. A drop in lactate, for instance, may mean reduced effort due to fatigue or improved fat-burning efficiency — the number alone does not tell you which.

"We are not merely mitochondria, dopamine, muscle mass, or blood-glucose spikes. We are beings in whom all these elements interact within our unique environments and personal histories."

Rather than fixating on a single parameter, it is essential to consider the whole system. Simply relying on a device to tell you when to train is a mistake — we must reconnect with our bodies and learn to listen to ourselves.

5.2. Prescribing Exercise Through RPE Metrics

Manuel clarifies a common misconception in training: we can control the stimulus we apply, but predicting how the body will adapt afterward is difficult. Training stimuli vary along three dimensions — type, magnitude, and frequency — and these dimensions interact with one another.

1. Type of stimulus: Refers primarily to which physiological structures are targeted. For example, high-intensity stimuli lasting under 10 seconds focus on fast-twitch fibers, while low-intensity stimuli such as endurance cycling mainly activate slow-twitch fibers and improve aerobic capacity.
2. Magnitude of the stimulus: Even the same low-intensity stimulus differs enormously between 30 minutes of cycling and 6 hours of cycling. Greater magnitude produces greater physiological stress.
3. Frequency: Determines how often high-intensity stimulus sessions can be repeated. Greater magnitude requires longer recovery periods to allow adequate adaptation and prevent overtraining.

When designing training, he focuses on creating specific types of stimuli at varying magnitudes — aerobic capacity sessions lasting over an hour, aerobic power sessions lasting 3–6 minutes, aerobic capacity-intensity sessions lasting 30 seconds to 3 minutes, and neuromuscular power sessions. For low-intensity training, he uses heart rate or perceived effort as a guide, providing internal load feedback that helps manage accumulated fatigue and adjust training intensity accordingly.

5.3. Intensity Prescription Based on Peak Perceived Effort

There are two ways to measure training intensity. The first is the average RPE for the entire session — for example, rating a 4-hour ride an overall 5 or 6 out of 10. The second is the peak RPE within a specific set or interval.

"For example, during aerobic power training with three sets of 1-minute efforts at close to maximum sustainable power, the final set might see RPE climb to 7, 8, or even 9 — indicating a high stimulus magnitude of 9 out of 10."

Determining the appropriate magnitude of a training stimulus is critical. It requires careful consideration of the athlete's recovery capacity from the previous week or session. Balancing intensity and recovery is challenging, but Manuel says that during phases focused on maintaining health, he aims to avoid sessions that cause excessive fatigue and targets full recovery within 48 hours. Typically RPE targets fall between 7 and 9, with roughly one session per week reaching 9.

Conversely, during race-specific training phases, the goal shifts to pushing limits and achieving maximum adaptation. In these periods he prescribes harder intervals reaching RPE 9 or even 10 two to three times per week. These sessions are strategically interspersed with easier recovery days to create a polarized training approach. On other weeks, training load remains more balanced and stable to prevent overtraining.

6. Recovery and Adaptation in Training 😴💪

In designing a training program, Manuel emphasizes a smooth, easy-to-follow flow. The key is to train hard when the body is ready and to ease off when fatigue accumulates. 📉 Occasionally training when tired or unmotivated is fine, but it should be rare. Understanding the body's signals and respecting the need for rest and recovery is essential.

Many people rely heavily on training metrics and assume more training means more progress. But the relationship between training load and improvement is not linear. Metrics like CTL (Chronic Training Load) or Strava's fitness score may indicate increasing training volume without necessarily reflecting actual performance gains.

"Many people rely heavily on training metrics and assume more training means more progress. But the relationship between training load and improvement is not linear."

For less experienced individuals, increasing training load may initially produce improvement simply because they are transitioning from no training at all to regular training. For experienced athletes, however, there is a subtler balance where excessive training can actually degrade performance. As a coach, he frequently sees athletes fall into the overtraining trap because of the mistaken belief that "more is always better."

Training is stress imposed on the body, and too much stress without adequate recovery leads to negative outcomes such as injury or stagnation. Cyclists in particular may experience rapid early improvement by pushing harder, but this often leads to a cycle of stagnation or regression caused by fatigue or injury. 😥

Patience matters in training. The goal is not to chase gains that disappear — it is to achieve long-term, sustainable adaptation. Listening to the body's signals and finding the balance between knowing when to push and when to back off is paramount. This approach not only improves performance but also helps athletes stay healthy and avoid burnout.

7. Training Zones and Thresholds 📊

In exercise physiology, we often discuss the concept of steady states, typically characterized by models such as critical power or FTP (Functional Threshold Power), which are based on a hyperbolic function. MFTP (Modeled Functional Threshold Power), for example, uses a power curve similar to the critical power model to estimate FTP. These models define the highest power output generally sustainable for about an hour without significant fatigue.

Manuel argues in his book that the power-duration relationship does not reveal a clear threshold. Analyzing world records from 1500m to the marathon on a logarithmic scale shows a consistent loss in power or speed, which contradicts the existence of a distinct threshold. In practice, he observes that every time sustainable duration doubles, the power an athlete can maintain drops by approximately 10%.

"For example, someone who can sustain 400 watts for 5 minutes can hold roughly 360 watts for 15 minutes and 324 watts for 45 minutes. This pattern challenges the notion of a stable plateau of power or speed."

As for physiological markers such as lactate threshold and oxygen consumption, while these provide valuable insight, the body's complex interactions mean thresholds fluctuate continuously. He cautions against treating zones or thresholds as fixed physiological limits.

"I caution against treating zones or thresholds as fixed physiological limits. They serve as useful training tools, but they should be understood as artificial constructs rather than absolute boundaries."

Understanding these concepts can enhance training strategy and shift the emphasis toward adaptability and long-term performance improvement, rather than fixating on rigid physiological interpretations.

8. The Influence of Psychology on Training 🧠

Slowing down in a race or a training session is not simply a matter of physical markers like lactate levels or heart rate. It happens when the effort becomes unbearable — regardless of what those markers read. Understanding this distinction is important, because endurance is not purely physical; it is the management of involuntary perceived effort, which is strongly influenced by motivation and mindset.

Endurance training encompasses three main domains:

1. Physical conditioning: Aimed at reducing physical burden.
2. Emotional component: Setting compelling goals that excite us, raising motivation and minimizing perceived effort.
3. Rational dimension: Building the willpower to continue exerting effort even when facing challenging circumstances.

Motivation depends on personal activation and our attitude toward the task. A compelling goal can reduce perceived effort, while an unappealing task can increase it. Goals should be ambitious yet achievable — enough to sustain motivation without becoming overwhelming.

The third component, mindset, concerns the ongoing negotiation between the perceived benefits and costs of effort. This dynamic process influences whether we keep pushing or pull back at the most intense moments of competition. What seemed manageable at the start can feel overwhelming as effort accumulates, affecting performance.

Competitive experience reveals how our perception of effort evolves throughout a race. Managing these dynamics requires mental skills honed through training and race experience, not quick fixes. Building endurance involves setting clear goals and gradually adapting to varying effort levels over time, so that the athlete is prepared for critical moments on race day.

9. The Importance of Training Environment 🏞️

The connection between an athlete and their environment plays a decisive role in performance and well-being. Manuel recalls his own racing career — particularly the transitions from a busy summer race schedule to high-altitude training camps. During those times, he would long for the comfort of home, familiar faces, and his regular routine.

"Back then, being at altitude felt like a struggle, and it noticeably affected my performance."

That experience made him realize the profound influence environmental factors have on athletic adaptation and success. It was not just about physical training — his emotional state, stress levels, and overall well-being significantly shaped his body's response to training stimuli. Research supports this: elevated stress levels, particularly raised cortisol, can interfere with the body's ability to adapt and recover optimally from training.

The training camp analogy is instructive. When athletes are immersed in a supportive, low-stress environment, removed from the demands of everyday life, they often find they can push training further. The relaxed atmosphere — combined with camaraderie and ideal training conditions — can produce results far more positive than a typical training week at home.

Fundamentally, humans are not closed systems; we constantly interact with and respond to our surroundings. Our physiological processes — including those critical to athletic performance — are intricately linked to our emotional and social contexts. Understanding and managing these environmental influences may therefore be just as important as fine-tuning training programs and nutrition strategies.

10. Thoughts on AI, Big Data, and New Device Trends 🤖📈

Manuel observes that we appear to be entering an era where more data is not necessarily the advantage — having the right framework to interpret and apply that data effectively is what matters. AI and machine learning can identify correlations among variables, but applying those insights to specific individuals requires understanding causal relationships, not merely associations.

When you factor in physiology, genetics, training history, motivation, emotional state, cultural influences, and countless other variables, determining what a given individual needs at a specific moment — and why — is enormously difficult. These factors interact and affect each person so differently that generalizing or building an "average elite" template is inherently complex.

Despite technological advances in data collection and analysis such as real-time monitoring, we often find that the promise of complete control over training outcomes falls short. Even with sophisticated tools like continuous glucose monitors or cycling power meters, the actual impact on training outcomes is limited. These technologies help with pacing and performance management but do not fundamentally change the process of becoming stronger or healthier.

"There is also concern that AI may reinforce biases or confine our thinking to predefined patterns, constraining innovation and progress. Language models, for example, reflect back what we put in — potentially entrenching existing ways of thinking."

Looking back at history, not every technological innovation in sports training has revolutionized performance in the way it was initially promoted. Each advance contributes incrementally rather than dramatically transforming results. Technology clearly enhances training, but we must maintain a realistic perspective on its actual impact and continue searching for genuinely innovative approaches beyond what current tools provide.

11. Common Mistakes Made by Athletes and Coaches 🤦‍♀️

Athletes who work with multiple coaches simultaneously can run into problems when those coaches fail to communicate with one another. This lack of communication can lead to conflicting or redundant training sessions, creating confusion and impeding progress. 🗣️ It is important for coaches to collaborate, or at minimum to access each other's training plans and athlete data through platforms like TrainingPeaks. That way, they can coordinate their efforts and ensure a coherent training approach that optimally supports the athlete's goals.

When communication among coaches is not possible, athletes must take responsibility for managing their own training intensity effectively. This means keeping the overall training load in mind and adjusting sessions as needed to avoid overtraining or undertraining. Group sessions can be motivating and practical, but they may not always align perfectly with an individual's long-term training plan. Athletes should consider adjusting their level of participation or effort in such sessions based on their fatigue and training objectives.

The balance between quality and quantity in training sessions is especially important for athletes who have experienced overtraining in the past. It is important not to push too hard in every session a group coach labels as hard. Instead, the occasional easier session provides the recovery needed and helps prevent burnout. This approach prioritizes the athlete's long-term health and performance sustainability over short-term gains.

Athletes should also focus on gradually rebuilding confidence in their training and overall health following a history of overtraining. This means listening to their bodies, making informed decisions about session intensity, and being willing to modify the training plan when necessary. By adopting a flexible, individualized approach to training, athletes can avoid the overtraining trap and maintain consistent progress toward their athletic goals.

12. Advice for Endurance Athletes 💡

Manuel's foremost advice to endurance athletes is to enjoy the training process. There are countless ways to reach success, and it is not always necessary to focus exclusively on hitting specific intervals or metrics. Sometimes a steady, comfortable run or ride can be equally beneficial, and mixing things up provides variety and the flexibility to train with friends. 🤝

Champions are built through years of consistent, uninterrupted training. Reaching the elite level requires finding satisfaction in the training process and the lifestyle that accompanies it. It is important not to obsess over too many metrics — while they can offer valuable insight, excessive focus on them can lead to training errors. Listening to your body's signals and daily sense of well-being is equally as important as relying on predefined fitness scores.

Viewing training through a holistic lens and avoiding excessive optimization is key. Performance is influenced by many factors that must work smoothly together. For example, the occasional social activity — sharing a glass of wine with a friend or a partner, or simply enjoying intimacy — can contribute positively to overall well-being. ❤️

Conclusion

The conversation with Manuel Sola Arjona delivers an important message: training should not be viewed as merely the sum of physiological markers. Instead, it calls for understanding humans as complex systems, approaching training from an evolutionary perspective, and holistically considering individual body signals, emotions, and environmental factors. Recognizing the dangers of reductionism, actively incorporating subjective measures of effort like RPE, and prioritizing recovery and sustainable progress are all essential. Technology advances training, but it does not solve everything — communication between coach and athlete, a personalized approach, and above all a genuine enjoyment of the training process are the keys to long-term success. 🌟