Overtraining Syndrome (OTS) Biomarkers: Monitoring Indicators for Cortisol, LH, and White Blood Cells

Overtraining Syndrome (OTS) is a decline in performance and systemic dysregulation caused by long-term training load exceeding recovery capacity. Early detection of OTS is a major challenge in athlete health management, and researchers continue to search for reliable biomarkers.

Based on research from leading international academic journals, this article systematically analyzes the scientific underpinnings of overtraining biomarkers. Starting from the methods and findings of key papers, we will delve into the underlying physiological mechanisms, quantify the relationship between training dose and effect, compare differences across populations, and ultimately translate these academic findings into actionable training recommendations for Taiwanese endurance athletes. This is not merely a compilation of knowledge, but a practical map leading from the laboratory to the training ground. In an era where it is difficult to distinguish truth from falsehood, returning to rigorous scientific evidence is the most worthwhile investment for any athlete who takes their training seriously.

Academic Research Review

The most effective way to understand this topic is to directly examine representative studies from leading international journals. Below is a compilation of several landmark or methodologically rigorous papers that, from different perspectives, collectively construct our current scientific understanding.

1. Meeusen et al. (2013, MSSE)

This study employed the European and American consensus statement on OTS. OTS diagnosis requires the exclusion of other diseases; there is no single marker. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions, and allowing us to move beyond the ambiguity of rule-of-thumb practices.

2. Urhausen and Kindermann (2002, Sports Medicine)

This study employed a comprehensive review of overtraining markers. It uses a combined assessment of hormonal and performance indicators. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions, and allowing us to move beyond the ambiguity of rule-of-thumb practices.

3. Lehmann et al. (1998, MSSE)

This study employed training load and hormonal analysis. It focuses on hypothalamic-pituitary axis dysregulation. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions, and allowing us to move beyond the ambiguity of rule-of-thumb practices.

4. Cadegiani and Kater (2017, BMC)

This study employed hormonal research on OTS. It is characterized by blunted multi-hormonal responses. The value of this study lies in its systematic approach to testing hypotheses, providing a quantifiable basis for subsequent training prescriptions, and allowing us to move beyond the ambiguity of rule-of-thumb practices.

Looking across the literature above, a common trend emerges: contemporary sports science increasingly emphasizes replacing intuition with objective data and rigorous experimental design. These studies echo and reinforce each other, collectively pointing to consistent core conclusions, giving us greater confidence when formulating training strategies. The next section will delve into the physiological mechanisms behind these phenomena.

Synthesis of Core Findings

OTS has no single reliable diagnostic marker and requires comprehensive assessment. Common indicators include: blunted exercise-induced hormonal responses (weakened cortisol, growth hormone, LH, etc. responses to exercise stimuli), abnormal resting and exercise heart rates, decreased HRV, performance decline, and mood disturbances. The most practical early warning signs are often a “decoupling of performance and heart rate during submaximal exercise” and persistent fatigue.

It is worth emphasizing that these findings are not isolated laboratory numbers, but robust conclusions repeatedly validated across different populations and study designs. Precisely because of this, they can serve as the scientific cornerstone for training prescriptions. However, between “research findings” and “training application,” there lies a layer of mechanistic understanding—only by figuring out the “why” can we make correct adjustments when facing individual differences and on-the-ground variables, rather than rigidly applying numbers. This is also the key dividing line between “an executor who follows the plan mechanically” and “an athlete who truly understands training”—the former merely replicates the schedule, while the latter can flexibly adjust every training decision based on their own condition, environmental changes, and race demands, maximizing the benefit of limited time and energy.

Core Physiological Mechanisms

Behind any training adaptation, a cascade of physiological changes operates from the molecular and cellular levels to the organ system level. Understanding these mechanisms helps us determine which training methods truly address the limiting factors of performance and which merely add fatigue with limited benefit. The table below summarizes the key physiological mechanisms closely related to this topic and their effects:

Mechanism/Adaptation	Physiological Change	Impact on Performance
HPA axis dysregulation	Blunted hormonal response	Impaired adaptation
Autonomic dysregulation	HRV↓, abnormal heart rate	Insufficient recovery
Performance decline	Unexplained regression	Core symptom

These mechanisms do not operate independently but are interwoven and mutually influential within an overall network. For example, without a simultaneous improvement in peripheral muscular metabolic capacity, the increased oxygen delivery from central cardiovascular adaptations cannot be effectively utilized, and vice versa. This “barrel effect” reminds us that comprehensive and balanced training stimuli often yield more lasting progress than extreme focus on a single point.

More importantly, the “timing” of these adaptations varies. Some changes (such as plasma volume expansion, neural coordination) can manifest within days to weeks, while others (such as cardiac structural remodeling, bone adaptation) require months or even years of accumulation. Understanding this temporal dimension helps us maintain reasonable expectations for training outcomes, avoiding the premature conclusion that a method is ineffective before giving it sufficient time—a key reason why many people give up halfway.

Training Dose-Response Relationship

“How much should I train?” is the most pressing question for every athlete. Sports science answers this using the concept of “dose-response”—a quantifiable relationship exists between training variables (intensity, frequency, duration, volume) and the magnitude of adaptation, but this relationship is almost never simply linear. Understanding the shape of the dose-response curve helps us find the “sweet spot” with the highest return on investment, avoiding both undertraining and overtraining.

The table below summarizes dose recommendations and expected effects under different scenarios as a reference for practical planning:

Subject/Scenario	Recommended Dose	Expected Effect
Load > Recovery	Long-term accumulation	OTS risk
Monitoring	HRV + heart rate + performance	Early detection
Management	Extended rest	Only solution

Several general principles can be derived from the table. First, diminishing marginal returns: as fitness levels rise, the training stimulus required to achieve the same magnitude of improvement increases, which is why elite athletes often measure progress in “fractions of a percent.” Second, ceiling effect: beyond a certain threshold, additional training volume not only yields sharply diminishing returns but may even be counterproductive due to fatigue accumulation. Third, individual threshold: the minimum effective dose required to trigger adaptation differs for each person, explaining why the same training plan produces vastly different results in different individuals.

Therefore, the smartest training strategy is not blindly pursuing “more,” but pursuing “just right”—providing sufficient stimulus to trigger adaptation, paired with adequate recovery to allow the adaptation to actually occur. Periodization is designed precisely to achieve this goal: through planned fluctuations in load, avoiding linear fatigue accumulation and allowing the body to peak at critical moments.

Differences Across Populations

A recurring and undeniable theme in research on overtraining biomarkers is “individual and population differences.” Applying the same conclusions indiscriminately to everyone is one of the most common errors in training prescription. Below, we analyze these differences from several key dimensions.

Beginners vs. Advanced Athletes: Beginners, being far from their physiological ceiling, respond significantly to almost any regular stimulus—this is the so-called “beginner’s bonus.” Highly trained athletes, however, have limited adaptive capacity and require more precise, higher-intensity, or more varied stimuli to continue progressing. This means the optimal training strategies for the two groups are fundamentally different; advanced athletes especially need to prioritize training “quality” and “specificity” over simply accumulating “quantity.”

Males vs. Females: In absolute values (such as absolute VO2max, muscle mass, hemoglobin concentration), males are generally higher than females, primarily due to differences in body size, hormones, and body composition. However, in “relative training responses” (percentage improvements), sex differences are often insignificant, and females benefit fully from various types of training. Notably, female menstrual cycles, hormonal fluctuations, and energy availability (RED-S risk) need special consideration in training planning.

Age Differences: With advancing age, maximal heart rate, muscle mass, recovery speed, and the hormonal environment all change. However, extensive research confirms that even middle-aged and older populations retain the capacity to adapt to training, though adaptation may be slower and require more recovery. In other words, “it’s useless to train when you’re old” is a complete myth. Older adults, in fact, need regular training even more to combat sarcopenia, bone loss, and cardiorespiratory decline.

Genetic Factors: Don’t forget the “responder–non-responder” phenomenon. Large family studies indicate that a considerable proportion of training response can be explained by genetics. This means that facing the same training plan, some improve dramatically while others progress slowly—often not due to lack of effort, but inherent differences in response potential. Recognizing this helps athletes maintain a healthier perspective on their own and others’ progress rates and encourages them to experiment with adjusting training modes to find stimuli that suit them.

Practical Training Application

The value of theory lies in guiding practice. Translating research findings on overtraining biomarkers into daily executable training requires grasping three key principles: “Specificity,” “Progression,” and “Monitorability.”

Specificity Principle: Training must target the energy systems and physiological adaptations required for the goal. If the goal is long-distance endurance, substantial aerobic base training is needed; to break through VO2max limits, targeted high-intensity interval stimuli are required. The most common problem with indiscriminate training is falling into the “moderate-intensity black hole”—every session is somewhat breathless but not hard enough, failing to effectively build the aerobic base while also missing the key high-intensity stimulus, ultimately leading to stagnation.

Progression Principle: The body only adapts when faced with loads slightly exceeding current capacity, but load increases must be gradual. A practical guideline is to “keep weekly training volume increases within approximately 10%” and schedule a deload week every 3–4 weeks to allow accumulated fatigue to dissipate and adaptations to consolidate. Rushing progress is the number one cause of injury and overtraining in amateur athletes.

Monitorability Principle: Replacing subjective feelings with objective data is the core of modern training. It is recommended to establish the following monitoring habits:

• Morning resting heart rate and heart rate variability (HRV): Reflects recovery status and autonomic nervous system balance; abnormally elevated resting heart rate or a sudden drop in HRV are warning signs of fatigue.
• Power or pace: Tracking output at the same intensity under standardized conditions is the most objective way to assess fitness progress.
• Subjective fatigue and sleep quality: Simple daily self-assessments can capture overall status beyond the numbers.
• Periodic testing: Conduct a standardized test (e.g., threshold power, time trial) every 6–12 weeks to objectively evaluate training effectiveness and adjust accordingly.

Integrating these principles, a mature training plan should be “building the base with high volume at low intensity, raising the ceiling with small amounts of high intensity, consolidating adaptations with adequate recovery, and navigating direction with objective data.” Rather than blindly chasing mileage numbers every day, it is better to rigorously execute 1–2 high-quality sessions per week and truly relax the rest of the time—this is the essence of quality over quantity.

Local Application in Taiwan

Taiwanese amateur athletes often suffer from insufficient recovery due to the叠加 of work and family stress on top of training, compounded by the high summer temperatures, making the risk of OTS non-negligible. It is recommended to establish simple monitoring (morning pulse, HRV, subjective fatigue and mood, submaximal pace-heart rate), and decisively reduce training volume when persistent decline and fatigue appear. The only solution for OTS is adequate rest.

Taiwan’s unique geographical and climatic conditions necessitate local adaptation when applying conclusions from international research. The hot, humid summers, mountainous terrain, and dense, diverse race culture are both challenges and advantages. By knowing how to leverage high-altitude resources like Hehuan Mountain and Wuling for altitude training, how to acclimatize to heat and manage hydration and electrolyte replacement in hot, humid environments, and how to adjust training focus based on the characteristics of Taiwanese races (such as a high proportion of climbing), Taiwanese endurance athletes can turn local conditions into a competitive advantage. Remember, any data from laboratories in temperate countries needs to be interpreted and applied against the reality of Taiwan’s training environment—this is the final mile for scientific training to take root locally.

Debunking Common Myths

There is often a significant gap between scientific findings and popular beliefs. Many “common sense” notions widely circulated in the sports community do not hold up to empirical scrutiny. Below, we debunk common myths related to this topic:

Myth 1: Overtraining can be overcome through willpower.

In reality, OTS requires reduced training and rest; pushing through makes it worse. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 2: There is a single test that can diagnose OTS.

In reality, OTS requires a comprehensive exclusionary diagnosis. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 3: Only elites get OTS.

In reality, amateurs combined with life stress are equally at high risk. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

The key to debunking myths lies in cultivating the habit of “demanding evidence.” Whenever you hear any training claim, ask yourself, “What research supports this? Which population does it apply to?” Only by relying on empirical evidence can we avoid plausible-sounding but false traps in the age of information overload and make truly beneficial training decisions.

Conclusion: From Evidence to Action

Looking across the academic research on overtraining biomarkers, several clear conclusions emerge. First, endurance performance is the result of synergistic action across multiple physiological systems; no single indicator or training method holds the key to success. Second, the essence of training is “precise stress plus adequate recovery,” not merely the accumulation of effort. Third, individual differences are ubiquitous; the best training plan is always “one tailored for yourself and continuously adjusted based on data.”

Looking ahead, sports science is rapidly advancing toward “precision individualization.” Advances in genomics, metabolomics, and wearable devices will eventually allow us to predict an individual’s response potential before training and fine-tune each session in real-time based on physiological data. For Taiwanese athletes and coaches, building a local physiological database and developing training models adapted to the local climate and races are crucial tasks for narrowing the gap with the world’s elite.

For every reader, the most important action recommendation remains the same: First, understand your physiological baseline through objective testing; then design training based on scientific principles; pair it with disciplined recovery and continuous monitoring; and be patient with progress. There are no shortcuts to building endurance, but there is a right direction. May this science-based analysis serve as a reliable guide on your training journey, accompanying you in pursuing your limits while also enjoying the purest joy of sport.

Related Reading

• Early Indicators of Non-Functional Overreaching: Biomarker Diagnostic Research
• Overtraining Syndrome (OTS): A Complete Scientific Guide to Identification, Prevention, and Recovery
• Overtraining Syndrome Detection Guide: Recognizing Warning Signs to Avoid Training Breakdown
• Identifying, Preventing, and Fully Recovering from Overtraining Syndrome (OTS)