Scientific Definitions of Lactate Threshold LT1 vs LT2: Key Updates from the MSSE 2023 Consensus Statement

Lactate threshold is a key indicator distinguishing the transition between aerobic and anaerobic metabolism, yet the definitions of LT1 (first threshold) and LT2 (second threshold) have long been inconsistent, with different laboratories employing different methods, leading to divergent training zone classifications. Clarifying the physiological significance of both is the cornerstone of scientific training.

This article, grounded in research from leading international academic journals, systematically dissects the scientific内涵 of the definitions of lactate thresholds LT1 and LT2. We will start from the methods and findings of key papers, 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 information authenticity is hard to discern, returning to rigorous scientific evidence is the most worthwhile investment for any athlete who takes their training seriously.

Academic Research Review

To understand this topic, the most effective approach 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. Poole et al. (2021, JAP)

This study integrates the concepts of critical power and lactate threshold. It clearly distinguishes LT1 as the first rise point of lactate and LT2 as the point corresponding to maximal lactate steady state. The value of this research 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 empirical rules.

2. Faude, Kindermann, and Meyer (2009, Sports Medicine)

This study employs a systematic review of lactate threshold concepts. It compiles 25 threshold definitions and offers standardization recommendations. The value of this research 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 empirical rules.

3. Jamnick et al. (2020, Sports Medicine)

This study offers a methodological critique of training intensity zones. It points out that using only % HRmax to delineate zones can result in errors of up to ±10%. The value of this research 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 empirical rules.

4. Binder et al. (2008, EJCPR)

This study focuses on threshold determination in exercise testing. It recommends a dual interpretation using both the 4 mmol/L value and the individual lactate curve inflection point. The value of this research 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 empirical rules.

Looking across the aforementioned literature, 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 towards consistent core conclusions, giving us greater confidence when formulating training strategies. The next section will delve deeper into the physiological mechanisms behind these phenomena.

Synthesis of Core Findings

LT1 roughly corresponds to a blood lactate level of 2 mmol/L, marking the transition from fat to carbohydrate metabolism, and represents the upper limit of the basic aerobic zone; LT2 roughly corresponds to the maximal lactate steady state (MLSS), representing the upper limit of sustainable high-intensity effort. The three-zone model (below LT1, LT1–LT2, above LT2) demonstrates greater physiological validity than the traditional five-zone heart rate model.

It is worth emphasizing that these findings are not isolated laboratory numbers, but robust conclusions repeatedly validated across different populations and research designs. Precisely because of this, they can serve as the scientific foundation 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 faced with individual differences and on-site variables, rather than rigidly applying numbers. This is also the critical dividing line between “an executor who blindly follows a plan” and “an athlete who truly understands training”—the former merely replicates workouts, while the latter can flexibly modify 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 lies a cascade of physiological changes operating from the molecular and cellular levels up to the organ system level. Understanding these mechanisms helps us judge which training methods truly target the limiting factors of performance and which merely add fatigue with limited benefit. The table below organizes the key physiological mechanisms closely related to this topic and their functions:

Mechanism/Adaptation	Physiological Change	Impact on Performance
LT1 (Aerobic Threshold)	Lactate production ≈ clearance, ~2 mmol/L	Upper limit of basic endurance zone
LT2 (Anaerobic Threshold/MLSS)	Lactate production slightly exceeds clearance limit	Upper limit of tempo/threshold zone
VO2max Zone	Rapid lactate accumulation	Intervals and sprints

These mechanisms do not operate independently but are interwoven into a holistic network that influences each other. For example, without a simultaneous improvement in peripheral muscle 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 lead to 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, skeletal adaptations) require months or even years of accumulation. Understanding this temporal dimension helps us maintain reasonable expectations for training outcomes, avoiding the mistake of declaring a method 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 concerning 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 organizes dose recommendations and expected effects under different scenarios as a reference for practical planning:

Population/Scenario	Recommended Dose	Expected Effect
Zone 1 <LT1	65–80% of training volume	Build aerobic base
Zone 2 LT1–LT2	~10%	Threshold tempo
Zone 3 >LT2	~10–15%	VO2max stimulus

Several general principles can be derived from the table. First, diminishing marginal returns: as fitness levels improve, the training stimulus required to achieve the same degree of progress becomes increasingly larger, which is why elite athletes’ improvements are often measured in “fractions of a percent.” Second, ceiling effect: beyond a certain threshold, additional training volume not only yields sharply diminishing benefits but may even backfire due to fatigue accumulation. Third, individual threshold: the minimum effective dose required to trigger adaptation varies from person to person, explaining why the same training plan yields 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

Regarding research on the definitions of lactate thresholds LT1 and LT2, one recurring and unavoidable theme 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.” Advanced athletes, however, have limited adaptive capacity and require more precise, higher-intensity, or more varied stimuli to keep progressing. This means the optimal training strategies for the two groups are fundamentally different. Advanced athletes especially need to prioritize training “quality” and “specificity” rather than simply stacking “volume.”

Male vs. Female: In absolute values (such as absolute VO₂max, muscle mass, and hemoglobin concentration), males generally exceed females, primarily due to differences in body size, hormones, and body composition. However, in “relative training response” (percentage-based improvements), the differences between sexes are often insignificant—females benefit fully from all types of training as well. Notably, the menstrual cycle, hormonal fluctuations, and energy availability (RED-S risk) in females need special consideration in training planning.

Age Differences: With advancing age, maximal heart rate, muscle mass, recovery speed, and the hormonal environment all change. Yet extensive research confirms that even middle-aged and older populations retain the capacity to adapt to training—adaptation may simply be slower and require more adequate 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 cardiopulmonary 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, given the same training plan, some improve dramatically while others progress slowly—often not due to insufficient effort but to innate differences in response potential. Recognizing this helps athletes maintain a healthier mindset about their own and others’ rate of progress, and makes them more willing to experiment with different training modes to find the stimulus that works for them.

Practical Training Application

The value of theory lies in guiding practice. Translating research findings on the definitions of lactate thresholds LT1 and LT2 into executable daily training requires grasping three core principles: “specificity,” “progression,” and “monitorability.”

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

Progression Principle: The body adapts only when faced with loads slightly above current capacity, but load increases must be gradual. A practical guideline is to keep weekly training volume increases within about 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. We recommend establishing the following monitoring habits:

• Morning resting heart rate and heart rate variability (HRV): These reflect recovery status and autonomic nervous system balance. An abnormally elevated resting heart rate or a sudden drop in HRV is an early warning sign of fatigue.
• Power or pace: Tracking output at the same intensity under standardized conditions is the most objective way to assess fitness progression.
• Subjective fatigue and sleep quality: Simple daily self-assessments capture overall status beyond the numbers.
• Periodic testing: Every 6–12 weeks, perform a standardized test (such as threshold power or a time trial) to objectively evaluate training effectiveness and adjust accordingly.

Integrating these principles, a mature training plan should be “building the base with large volumes of low intensity, raising the ceiling with small volumes 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 execute 1–2 high-quality sessions per week with discipline and truly relax the rest of the time—this is the essence of quality over quantity.

Local Application in Taiwan

Taiwanese gyms and sports centers have gradually introduced portable lactate analyzers. Cyclists can perform step tests on the track or on a trainer to establish their individual LT1/LT2, avoiding the direct application of formulas. In high temperatures, lactate clearance efficiency decreases, so threshold pace in summer should be slightly adjusted downward.

Taiwan’s unique geographical and climatic conditions mean that conclusions from international research must be localized before domestic application. The hot, humid summers, mountainous terrain, and dense, diverse racing culture are both challenges and advantages. By knowing how to leverage high-altitude resources such as Hehuan Mountain and Wuling for altitude stimulus, how to manage heat adaptation and hydration/electrolyte replacement in hot, humid conditions, 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 must be interpreted and applied against Taiwan’s real training environment—this is the final mile for scientific training to take root locally.

Debunking Common Myths

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

Myth 1: Lactic acid is the culprit behind fatigue.

In reality, lactate is an important fuel; fatigue is primarily caused by the accumulation of hydrogen ions and metabolic byproducts. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 2: 4 mmol/L is the threshold for everyone.

In reality, a fixed 4 mmol/L ignores individual differences; thresholds must be interpreted via the inflection point of the lactate curve. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

Myth 3: The anaerobic threshold is the limit of exercise.

In reality, effort above LT2 can still be maintained for short periods; the limit is determined by multiple factors. Blindly believing such myths wastes training time and energy at best, and leads to fatigue, stagnation, or even injury at worst.

The key to breaking myths lies in cultivating the habit of “asking for evidence.” Whenever you hear any training claim, ask yourself, “What research supports this? Which population does it apply to?” Only by grounding decisions in evidence can we avoid plausible-but-wrong traps in an age of information overload and make truly beneficial training decisions.

Conclusion: From Evidence to Action

Looking across the academic research on the definitions of lactate thresholds LT1 and LT2, we can draw several clear conclusions. First, endurance performance is the result of multiple physiological systems working in concert—no single metric or training method holds the exclusive key to success. Second, the essence of training is “precise stress plus adequate recovery,” not merely the accumulation of effort. Third, individual differences are everywhere; the best training plan is always the one “tailored to yourself and continuously adjusted based on data.”

Looking ahead, sports science is rapidly moving toward “precision individualization.” Advances in genomics, metabolomics, and wearable devices will eventually allow us to predict an individual’s response potential before training even begins, and to 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 race conditions are crucial steps toward closing the gap with the world’s best.

Returning to each 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 is no shortcut 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

• The Science of Lactate Threshold Training: Physiological Mechanisms and Training Applications of LT1 and LT2
• The Science of Lactate Threshold Runs: Training Zones for LT1 and LT2
• Maximal Lactate Steady State and Power Meter Training: Standardization Research on MLSS Testing Methods
• Lactate Threshold Testing Methods: Accuracy Comparison Between Laboratory and Field Tests