Lactate Metabolism Changes Under High Temperatures: Research on the Effects of Heat Stress on Anaerobic Threshold

Based on the Journal of Applied Physiology, Medicine & Science in Sports & Exercise, Sports Medicine, and other international peer-reviewed journals, this article provides an in-depth analysis of the environmental physiological mechanisms behind “the effects of heat on lactate threshold,” and combines Taiwan’s subtropical climate, mountainous terrain, and local race scenarios to offer evidence-based training and race preparation strategies.

In the field of environmental physiology, “the effects of heat on lactate threshold” is one of the key variables that determines whether endurance athletes can perform at their best on a real race course. Many amateur and elite athletes focus their training on power output, pacing, and equipment, yet underestimate the enormous physiological impact of the environment—heat, cold, high altitude, humidity, and air quality. In fact, when two athletes have similar fitness and equipment, the one who better understands how to adjust strategies in response to the environment is often the one who can maintain pace in the latter stages of a race and avoid collapse or unexpected mishaps. Taiwan’s geographical environment is particularly unique: hot and humid summers, cold and damp winters, extreme elevation changes from sea level to Wuling at 3,275 meters, plus urban air pollution and typhoon season—all of which make environmental physiology especially valuable in practical terms for the local sports community. This article will take you from cellular and systemic physiological mechanisms, through empirical research published in top international journals, quantitative dose-response relationships, differences in responses across populations, and then to directly applicable training strategies and Taiwan-specific scenarios. Finally, we will debunk long-standing myths circulating in the community, so that your understanding of “the effects of heat on lactate threshold” is truly built on science rather than hearsay.

Academic Research Review

Regarding the scientific exploration of “the effects of heat on lactate threshold,” the field of environmental physiology has accumulated rigorous and rich evidence. Below are several representative studies selected for their value in methodological design, subject populations, and strength of conclusions, which together form our current understanding:

1. Febbraio et al. (1994). Journal of Applied Physiology confirmed that heat accelerates muscle glycogenolysis and lactate production.

2. Lu, Cheng & Chuang (2014). Journal of Thermal Biology examined the effects of heat stress on lactate kinetics.

3. González-Alonso et al. (1999). Journal of Applied Physiology analyzed the interaction between heat-induced dehydration and metabolism and circulation.

4. Nybo (2008). Journal of Applied Physiology reviewed central and metabolic fatigue mechanisms under heat stress.

Taken together, these studies show that the scientific picture of “the effects of heat on lactate threshold” has been continuously refined as measurement techniques have advanced. Early studies typically manipulated temperature, humidity, or partial pressure of oxygen in environmental chambers and observed changes in VO₂max, time to exhaustion, or time-trial performance; subsequent research introduced ingestible core temperature capsules, near-infrared spectroscopy, stable isotope tracers, muscle biopsies, and molecular markers, allowing us to move from “phenomenological observation” to “mechanistic explanation.” It is worth noting that most high-quality studies employed randomized crossover designs, where each subject served under both experimental and control conditions, greatly reducing the noise of individual differences. However, extrapolation of research conclusions still requires caution: a single environmental variable controlled in the laboratory does not necessarily equate to the complex combination of heat, humidity, wind, radiation, and fatigue encountered on a real race course; likewise, responses from well-trained subjects may not apply to the general amateur population. When interpreting “statistical significance” and “effect size,” we must also distinguish between average trends in the laboratory and practical meaning for an individual on race day—a 3% performance difference may determine placing in elite competition, while its significance for a recreational rider is relatively limited. It is precisely this careful consideration of evidence quality and applicability that forms the foundation of scientific training.

Core Mechanisms

Heat alters metabolic pathways during exercise, causing lactate to accumulate at lower intensities. The mechanisms include: heat increases sympathetic nervous system activity and epinephrine, stimulating muscle glycogenolysis and glycolysis, thereby increasing lactate production; simultaneously, dehydration and reduced plasma volume decrease blood flow perfusion to muscles and the liver, slowing lactate clearance; elevated core temperature also raises overall metabolic rate and carbohydrate dependence. The result is that the power or speed corresponding to the “lactate threshold” often shifts downward under heat—the same intensity produces higher blood lactate on hot days, and the sustainable threshold pace decreases. This means that threshold power or pace measured in cool conditions will be overestimated in hot, humid environments and should not be applied directly. In practice, threshold training and race pacing in hot environments must be adjusted downward, using power combined with perceived exertion to avoid early lactate accumulation and late-race collapse.

To truly understand how “the effects of heat on lactate threshold” influence athletic performance, one must return to the systemic integration of thermoregulation, cardiovascular, respiratory, metabolic, and central nervous systems. Environmental factors translate into measurable performance differences precisely because they act on one or more key links in this physiological chain—whether by limiting oxygen and fuel delivery, disrupting heat dissipation and fluid balance, or altering central perceptions of fatigue and motor drive. The table below summarizes the key effects of this topic at different physiological levels, helping you build a complete mechanistic picture:

| Physiological Level | Key Mechanisms | Implications for Athletic Performance |

|—|—|—|

| Cardiovascular System | Affects blood flow distribution, stroke volume, and circulatory capacity | Determines oxygen delivery and stability during prolonged exercise |

| Thermoregulation/Fluid Balance | Regulates heat dissipation pathways, sweat rate, and electrolyte balance | Affects rate of core temperature rise and dehydration risk |

| Muscle and Metabolism | Alters substrate utilization, enzyme activity, and contractile function | Determines sustainable power output and timing of fatigue onset |

| Central Nervous System | Modulates perceived fatigue, motor drive, and cognitive decision-making | Affects “how tired it feels” and the ability to persist and make safe judgments |

Particular emphasis should be placed on the two dimensions of “dose-response” and “temporal dynamics.” The same environmental exposure, under different intensities, durations, and acclimatization states, can produce vastly different or even opposite effects—this is precisely why many popular recommendations are one-sided. The limiting factors of athletic performance also shift dynamically with context: for short-duration, high-intensity efforts, limitations come primarily from anaerobic energy supply and local metabolism; for multi-hour endurance events, the focus shifts to the combined effects of rising core temperature, fluid imbalance, glycogen depletion, and central fatigue. “The effects of heat on lactate threshold” deserves in-depth exploration precisely because it can specifically target some of these limiting factors. Only by understanding the mechanisms can we determine “what adjustments to make in which environment, how much to adjust, and when to adjust,” rather than being led by the environment on race day. The more thoroughly you understand the mechanisms, the more flexibly you can respond across different situations such as heat, cold, high altitude, or pollution—this ability to adapt to context is precisely the dividing line between those who understand environmental physiology and those who train blindly.

Dose-Response Relationship

In environmental physiology, “dose determines effect” is a core principle. Environmental stimuli that are too low fail to reach the physiological threshold, producing no adaptation or impact; excessive exposure may exceed the body’s compensatory capacity, triggering risks such as heat injury, hypothermia, and altitude sickness. The table below summarizes the dose-response correspondence for “the effect of heat on lactate threshold,” serving as the most important quantitative reference when designing training and race preparation plans:

| Dose / Condition | Physiological State | Effect and Key Points |

|—|—|—|

| Cool environment | Lactate threshold baseline | Standard pace |

| Heat | Accelerated glycolysis | Higher lactate at same intensity |

| Dehydration叠加 | Slower clearance | Threshold shifts downward |

| Using cool-weather pace in heat | Earlier accumulation | Late-race collapse |

As shown in the table above, the effects of environmental exposure often follow a threshold-type or inverted U-shaped curve: before reaching the effective dose, adaptation or impact increases with dose; but beyond a certain critical point, there are not only no additional benefits—risk and cost rise sharply instead. This means that “finding your own optimal exposure” matters far more than “relentlessly pursuing extremes.” Whether it’s the daily heat dose for heat adaptation, the altitude and duration of altitude training, or exposure time in cold environments, there exists a sweet spot that balances benefit and safety. It is recommended to progressively test responses under different environmental conditions during training (not on race day), recording core temperature or heart rate, perceived exertion, power data, and recovery status to build your own environmental response profile. Remember: the laboratory average is a starting point, not an endpoint; everyone’s body type, sweat rate, adaptation level, and genetic background cause the optimal dose to shift individually—only by calibrating with your own data can you translate population science into a personal prescription.

Differences Across Populations

The impact of “the effect of heat on lactate threshold” is not equal for everyone. Age, sex, training status, body type, adaptation state, and genetic background all significantly modulate an individual’s response magnitude to the environment. Ignoring these differences and applying a one-size-fits-all recommendation is one of the most common errors in applied environmental physiology.

| Population Dimension | Response Characteristics | Practical Recommendations |

|—|—|—|

| Beginners vs. Advanced | Advanced athletes have more mature environmental adaptation and better tolerance, but less marginal adaptation capacity | Beginners should be conservative and progressive, building baseline tolerance before increasing load |

| Male vs. Female | Body surface area-to-weight ratio, hormonal cycles, and sweat composition differ | Females should receive individualized assessment of heat dissipation and hydration, and monitor energy availability |

| Young vs. Older | Older individuals have declining thermoregulation, sweat gland function, and compensatory capacity | Older individuals are more sensitive to extreme environments and need greater caution and longer adaptation periods |

| Body Type Differences | Body surface area, body fat, and muscle mass affect heat dissipation and heat production | Larger individuals dissipate heat less efficiently; smaller individuals cool down faster—each carries its own risks |

When interpreting individual differences, one must also be wary of a statistical trap: studies mostly report “group average responses,” but beneath the average often lies enormous individual variability. In the same environmental intervention, some may be strong responders, some barely respond, and some may even respond in the opposite direction. This is why even when a study shows “effective on average,” you still need to confirm through your own experimentation which category you fall into. It is recommended to conduct personalized controlled tests: across two training sessions under similar conditions, with and without a given environmental strategy (e.g., pre-cooling, heat adaptation), compare power, core temperature, heart rate, and subjective perception, repeating several times before drawing conclusions.

Taking Taiwan’s common amateur endurance population as an example, many are masters athletes over 35 who train around work commitments. This group’s thermoregulation and recovery capacity are already somewhat inferior to young elites; when facing the humid summer heat and high-altitude challenges, correct environmental strategies (heat adaptation, individualized hydration, gradual ascent) can yield relatively greater safety and performance benefits. Female athletes, meanwhile, need to pay attention to the effects of the menstrual cycle on baseline core temperature and fluid regulation, as well as whether energy availability is sufficient. After understanding population differences, you will realize: truly professional environmental physiology advice is always an individualized prescription that “varies from person to person,” never a one-size-fits-all slogan.

Practical Training Application

Theory must ultimately translate to training plans and race courses. Below is a practical framework for converting “the effect of heat on lactate threshold” into concrete training and race-day operations:

• Pre-race environmental rehearsal: All environmental strategies must first be rehearsed in training—“never try anything new on race day” is an iron rule. Whether heat adaptation, pre-cooling, or hydration pacing, the body needs time to build tolerance and proficiency.

• Periodization mindset: Align environmental adaptation with the training cycle—build tolerance during the base phase, and conduct sport-specific environmental adaptation during the pre-race phase targeting the temperature, humidity, or altitude of the goal event.

• Progressive exposure: Start with mild environmental stimuli and gradually increase load based on bodily responses, building a personalized exposure dose and timing profile to avoid injury from a single excessive exposure.

• Objective data monitoring: Combine core temperature (or heart rate drift), power, rating of perceived exertion (RPE), and urine/body weight changes to objectively assess whether environmental strategies are truly effective.

• Holistic context: Environmental adaptation is one component of training, sleep, recovery, and nutrition; no single strategy can compensate for sleep deprivation, dehydration, or flawed training design.

Using a one-week training schedule as an example, different environmental scenarios can be rehearsed across key midweek sessions and weekend long rides: high-intensity days focus on maintaining power quality in the target environment and testing heat dissipation or insulation gear; long-distance days focus on hydration and sodium pacing, thermoregulation, and long-duration gear tolerance. Through repeated rehearsal, the body can respond to the environment in a near-automatic manner on race day, freeing mental resources for pacing and tactical decisions. The most common mistake many people make is “taking the environment seriously only on race day while treating daily training casually”—this is precisely putting the cart before the horse. Daily training is the ideal laboratory for building heat tolerance, testing hydration doses, familiarizing yourself with gear, and cultivating environmental response rhythms.

It is recommended to integrate an environmental log with your training log, recording temperature, humidity, altitude, wind conditions, environmental strategies employed, bodily responses, and performance data for each key session. Over weeks to months of accumulation, the value of this personalized database will far exceed any generic guide. Furthermore, don’t overlook the often-underestimated aspect of “recovery under environmental stress”—heat or altitude slows recovery and exacerbates fatigue accumulation. The quality of recovery between consecutive training days often determines whether you can steadily accumulate training volume without injury, and training volume is the most fundamental engine of long-term progress. Treat environmental management as a serious part of training rather than a last-minute accessory before race day, and both your progress and safety will be markedly different.

Local Application in Taiwan

Taiwan’s unique climate, terrain, and race culture add a distinctly local flavor to the application of “the effect of heat on lactate threshold.” Summer heat and humidity are extreme—apparent temperatures often exceed 35°C and relative humidity frequently surpasses 80%—making evaporative cooling inefficient and sweat and electrolyte losses far greater than the research scenarios of temperate countries. This means recommendations from foreign literature often need upward adjustment. In winter, the northeast monsoon brings damp cold and strong winds, and mountainous areas carry risks of low temperatures and hypothermia. And the extreme elevation gain from sea level to Wuling at 3,275 meters puts high-altitude physiological challenges right at your doorstep.

Taking events such as the Westbound Wuling Challenge, Tour of East Taiwan, Sun Moon Lake Loop, Taroko Marathon, various triathlons, and island-wide cycling challenges as examples, athletes should factor local and seasonal environmental conditions into their planning: summer events should start earlier to avoid high afternoon WBGT, and take advantage of the dense convenience store network along routes to strengthen fluid and sodium replenishment; high-altitude sections should allow for gradual acclimatization, with attention to cold protection and signs of altitude sickness; winter damp-cold events require reinforced windproofing, insulation, and hypothermia protection. By making good use of the Central Weather Administration’s forecasts for apparent temperature, humidity, wind speed, and air quality—converting them into daily environmental risk assessments and strategies—you can balance safety and peak performance in Taiwan’s varied and demanding environment.

Common Myth-Busting

Myth: “Threshold power is fixed; weather doesn’t affect it.” High temperatures accelerate glycolysis and slow lactate clearance, so the same power output produces higher lactate in hot conditions, shifting the actual sustainable threshold downward; threshold pacing in hot environments must be adjusted downward and cannot simply follow data from cooler days.

These myths spread widely because they “sound reasonable,” are easy to pass along by word of mouth, or are amplified by marketing and anecdotal experience. Yet the value of science lies precisely in testing intuition with rigorous evidence: many seemingly obvious environmental beliefs fall apart under controlled environmental-chamber experiments and epidemiological investigations. Environmental physiology is especially full of oversimplified claims that compress complex dose, timing, individual variation, and risk into a single slogan. The next time you hear a categorical environmental recommendation, it’s worth asking: “What is the level of evidence for this claim? Who is it intended for? Are the dose, timing, and safety margins clearly defined?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for athletes toward a more scientific approach and avoiding environmental harm.

Conclusion

“The effect of heat on lactate threshold” is a topic in environmental physiology that combines theoretical depth with practical value. From the international journal evidence reviewed in this article, it is clear that the environment’s impact on athletic performance is real and profound—but by no means unmanageable—the key lies in understanding the mechanisms, mastering the dose, individualizing adjustments, and coordinating with overall training, recovery, and nutrition. For endurance sports enthusiasts in Taiwan, while grasping the scientific principles, it is equally important to integrate the local hot-humid climate, extreme altitudes, and variable weather, transforming general rules into personalized prescriptions suited to oneself. May every cyclist and runner sweating on Wuling, in the rift valleys, and along the island-circumnavigation route protect themselves through the wisdom of environmental physiology—against heat, cold, high altitude, and various challenges—push their limits, and enjoy the purest joy of sport. Before you next step onto the course, don’t forget—your true opponent is not just the timer, but the entire environment beneath your feet and all around you.

Related Reading

• Carbohydrate Metabolism Changes at High Altitude: The Impact of Hypoxia on Energy Utilization
• Physiological Mechanisms of Heat Acclimation: A Longitudinal Study of Plasma Volume Expansion and Sweat Rate Increase
• Cognitive Function Impairment in Hot Environments: The Impact of Heat Stress on Decision-Making Ability
• The Impact of Climate Change on Taiwanese Cycling Events: A Physiological Prediction Study of Rising Temperatures