Acute Effects of Air Pollution (PM2.5) Exposure on Endurance Cycling Performance: A Research Review

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 physiology mechanisms behind “the impact of PM2.5 exposure on endurance performance.” It also integrates Taiwan’s subtropical climate, mountainous terrain, and local race scenarios to offer evidence-based training and race preparation strategies.

In the realm of environmental physiology, “the impact of PM2.5 exposure on endurance performance” is one of the key variables that determines whether an endurance athlete can perform at their true potential 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 according to the environment is often the one who can maintain pace in the latter stages of a race, avoiding collapse and mishaps. Taiwan’s geography is particularly unique: hot and humid summers, cold and damp winters, extreme elevation gains from sea level to Wuling at 3,275 meters, plus urban air pollution and typhoon season, making environmental physiology exceptionally valuable in practice for the local sports community. This article will guide you from cellular and systemic physiological mechanisms, through empirical research in top international journals, quantitative dose-response relationships, and differences in responses across populations, to directly actionable training applications and Taiwan-specific scenarios. Finally, we will debunk long-standing myths, so your understanding of “the impact of PM2.5 exposure on endurance performance” is truly built on science, not hearsay.

Academic Research Review

The scientific exploration of “the impact of PM2.5 exposure on endurance performance” has accumulated rigorous and rich evidence in the field of environmental physiology. Below are several representative studies selected for their value in methodological design, study populations, and strength of conclusions, which together form our current understanding:

1. Rundell (2012). Sports Medicine reviewed the acute and chronic effects of air pollutants on lung function and performance in athletes.

2. Cutrufello et al. (2012). Sports Medicine compiled evidence on the effects of particulate matter and ozone exposure on exercise-induced airway responses.

3. Giles & Koehle (2014). Sports Medicine systematically reviewed the dose-response relationship between air pollution and exercise performance and health.

4. Pasqua et al. (2018). Frontiers in Physiology quantified the impact of PM exposure on cyclists’ respiration and performance during real urban riding.

Looking across these studies, it is clear that the scientific picture of “the impact of PM2.5 exposure on endurance performance” has deepened with advances in measurement technology. Early studies typically manipulated temperature, humidity, or partial pressure of oxygen in environmental chambers, observing changes in VO₂max, time to exhaustion, or time-trial performance; later studies introduced ingestible core temperature capsules, near-infrared spectroscopy, stable isotope tracers, muscle biopsies, and molecular markers, allowing us to move from “observing phenomena” to “explaining mechanisms.” Notably, most high-quality studies employed randomized crossover designs, where each subject served as both the experimental and control condition, greatly reducing noise from 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 on a real race course; nor do responses from well-trained subjects necessarily apply to general amateurs. When interpreting “statistical significance” and “effect sizes,” 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 attention to the level of evidence and scope of applicability that forms the foundation of scientific training.

Core Mechanisms

During exercise, minute ventilation can reach 10 to 20 times resting levels, and breathing shifts predominantly to oral breathing, bypassing nasal filtration, which greatly increases the deposited dose of pollutants in the lungs. Fine particulate matter PM2.5 can penetrate deep into the alveoli, triggering airway inflammation, oxidative stress, and bronchoconstriction, increasing the work of breathing and reducing ventilatory efficiency; ozone and nitrogen dioxide irritate the airways and exacerbate exercise-induced bronchoconstriction. On an acute level, high-pollution exposure can reduce ventilatory efficiency during submaximal exercise, increase perceived exertion, and mildly suppress endurance performance; oxidative stress may also interfere with vascular endothelial function. Chronic repeated exposure is associated with chronic airway inflammation and cardiovascular risk. The higher the exercise intensity, the longer the exposure duration, and the higher the pollutant concentration, the greater the cumulative dose.

To truly understand how “the impact of PM2.5 exposure on endurance performance” affects athletic performance, we 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—either limiting oxygen and fuel delivery, interfering with 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 | Significance for Athletic Performance |

|—|—|—|

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

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

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

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

Two dimensions deserve particular emphasis: “dose-response” and “temporal dynamics.” The same environmental exposure, under different intensities, durations, and states of acclimatization, 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: short-duration, high-intensity performance is primarily limited by anaerobic energy supply and local metabolism, while multi-hour endurance shifts toward the combined effects of rising core temperature, fluid imbalance, glycogen depletion, and central fatigue. “The impact of PM2.5 exposure on endurance performance” deserves in-depth exploration precisely because it can specifically affect some of these limiting factors. Only by understanding the mechanisms can we determine “how to adjust for a given environment, by how much, and when,” rather than being led around 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 according to context is the dividing line between those who understand environmental physiology and those who train blindly.

Dose-Response Relationships

In environmental physiology, “the dose determines the effect” is a core principle. Environmental stimuli that are too low fail to reach physiological thresholds, producing no adaptation or effect; excessive exposure may exceed the body’s compensatory capacity, leading to risks such as heat injury, hypothermia, or altitude sickness. The table below outlines the dose-response correspondence for “the impact of PM2.5 exposure on endurance performance” and serves as the most important quantitative reference when developing training and race preparation plans:

| Dose / Condition | Physiological Status | Effects and Key Points |

|—|—|—|

| PM2.5 <15 μg/m³ | Good | Normal outdoor training is fine |

| 15–35 μg/m³ | Moderate / Sensitive | Reduce high-intensity outdoor training |

| 35–54 μg/m³ | Unhealthy for sensitive groups | Shorten high-intensity sessions; move indoors |

| >54 μg/m³ | Unhealthy | Avoid high-intensity outdoor training |

As the table shows, the effects of environmental exposure often follow a threshold or inverted U-shaped curve: before reaching an effective dose, adaptation or effects increase with dose; but beyond a certain critical point, not only are there no additional benefits, but risks and costs rise sharply. This means that “finding your optimal exposure” matters far more than “chasing extremes.” Whether it’s the daily heat dose for heat acclimation, the altitude and duration for altitude training, or exposure time in cold environments, there is a sweet spot that balances benefit and safety. It is recommended to progressively test your 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: laboratory averages are a starting point, not the endpoint; each person’s body size, sweat rate, acclimatization status, and genetic background will shift the optimal dose individually. Only by calibrating with your own data can you translate population science into a personal prescription.

Differences Across Populations

The impact of “PM2.5 exposure on endurance performance” is not equal for everyone. Age, sex, training status, body size, acclimatization state, and genetic background all significantly modulate an individual’s magnitude of response to the environment. Ignoring these differences and applying a one-size-fits-all recommendation is one of the most common errors in the application of environmental physiology.

| Population Aspect | Response Characteristics | Practical Recommendations |

|—|—|—|

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

| Male vs. Female | Differences in body surface area-to-mass ratio, hormonal cycles, and sweat composition | Females should individually assess heat dissipation and hydration, and pay attention to energy availability |

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

| Body Size Differences | Body surface area, body fat, and muscle mass affect heat dissipation and heat production | Larger individuals have more difficulty dissipating heat; smaller individuals cool faster—each has its own risks |

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

Take Taiwan’s common amateur endurance population as an example: many are middle-aged cyclists and runners over 35 who train around work schedules. This group’s thermoregulation and recovery capacity are already somewhat inferior to younger elites. When facing hot, humid summers and high-altitude challenges, correct environmental strategies (heat acclimation, individualized hydration, progressive ascent) can yield relatively greater safety and performance benefits. Female athletes should 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 by person, never a one-size-fits-all slogan.

Practical Training Applications

Theory must ultimately translate into training plans and race-day execution. Below is a practical framework for turning “the impact of PM2.5 exposure on endurance performance” into concrete training and competition operations:

• Pre-race environmental rehearsal: All environmental strategies must be practiced in training first. “Never try anything new on race day” is an iron rule. Whether it’s heat acclimation, pre-cooling, or hydration pacing, the body needs time to build tolerance and familiarity.

• Periodization mindset: Align environmental adaptation with your training cycle—build tolerance during the base phase, and conduct sport-specific environmental acclimatization for the target race’s temperature, humidity, or altitude during the pre-race phase.

• 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 part 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, you can rehearse different environmental scenarios in key midweek sessions and weekend long rides: on high-intensity days, focus on maintaining power quality in the target environment and testing cooling or insulation gear; on long-distance days, focus on hydration and sodium pacing, thermoregulation, and long-duration tolerance of equipment. Through repeated rehearsal, your body can respond to the environment in an almost automated way on race day, leaving mental resources for pacing and tactical decisions. The most common mistake people make is “only seriously dealing with the environment on race day while treating daily training casually”—this is precisely putting the cart before the horse. Daily training is the best laboratory for building heat tolerance, testing hydration doses, familiarizing yourself with gear, and developing an environmental response rhythm.

It is recommended to integrate an environmental log with your training log, recording temperature, humidity, altitude, wind conditions, environmental strategies used, bodily responses, and performance data for each key session. After weeks to months of accumulation, the value of this personalized database will far exceed any general guide. Additionally, don’t overlook the often-underestimated aspect of “recovery in the environment”—heat or high altitude slows recovery and increases 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, not a last-minute accessory before race day—your progress and safety will both be noticeably different.

Taiwan-Specific Applications

Taiwan’s unique climate, terrain, and race culture add a distinct local flavor to the application of “the impact of PM2.5 exposure on endurance performance.” In summer, high heat and humidity mean the apparent temperature often exceeds 35°C with relative humidity frequently above 80%, making evaporative cooling inefficient and sweat and electrolyte losses far greater than in research scenarios from temperate countries—this means recommendations from foreign literature often need to be adjusted upward. In winter, the northeast monsoon brings cold, damp conditions and strong wind chill, and mountainous areas may present risks of low temperatures and hypothermia. Meanwhile, 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 tours as examples, athletes should factor local and seasonal environmental conditions into their planning: summer races should start earlier to avoid high WBGT in the afternoon, and take advantage of the dense convenience store network along routes to strengthen fluid and sodium replenishment; high-altitude sections should allow for progressive acclimatization, with attention to cold protection and signs of altitude sickness; winter cold, damp races require stronger windproofing, insulation, and hypothermia protection. Make 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, so you can balance safety and optimal performance in Taiwan’s varied and demanding environment.

Debunking Common Myths

Myth: “Wearing a regular mask while cycling can block PM2.5.” Most cloth masks have limited filtration of fine particulate matter, and during exercise, high ventilation rates and air leakage greatly reduce protection; what truly works is avoiding high-pollution times and locations, or switching to indoor training.

Such myths spread widely because they “sound reasonable,” are easily passed from person to person, or are amplified by marketing and anecdotal experience. Yet the value of science lies in testing intuition with rigorous evidence: many environmental beliefs that seem self-evident do not hold up under controlled environmental chamber experiments and epidemiological investigations. The field of environmental physiology is especially rife with oversimplified claims that compress complex dose, timing, individual differences, and risks into a single slogan. The next time you hear a definitive environmental recommendation, it’s worth asking: “What is the level of evidence for this claim? Who is it applicable to? Are the dose, timing, and safety margins clear?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for athletes toward scientific training and avoiding environmental harm.

Conclusion

“The impact of PM2.5 exposure on endurance performance” is a topic in environmental physiology that combines theoretical depth with practical value. As the international journal evidence reviewed in this article shows, the environment’s impact on athletic performance is real and profound, but by no means unmanageable—the key lies in understanding mechanisms, mastering dose, individualizing adjustments, and coordinating with overall training, recovery, and nutrition. For endurance sports enthusiasts in Taiwan, while grasping scientific principles, it is equally important to integrate the local hot, humid climate, extreme altitude, and variable weather, transforming general principles into personalized prescriptions that suit you. May every cyclist and runner sweating on Wuling, in the East Rift Valley, or on island-wide routes harness the wisdom of environmental physiology to protect themselves, push their limits, and enjoy the purest joy of sport amid heat, cold, high altitude, and all kinds of challenges. Before you next step onto the race course, remember—your true opponents are not just the clock, but the entire environment beneath your feet and all around you.

Related Reading

• Cycling Conditions During Taiwan’s Northeast Monsoon: A Study of the Physiological Effects of Low Temperature and Wind Chill
• Performance Differences Between Maritime and Continental Climates: A Taiwan Case Study
• The Impact of Climate Change on Taiwan’s Cycling Events: A Physiological Prediction Study of Rising Temperatures
• Physiological Responses to Cold-Weather Cycling: Research on Vasoconstriction, Muscle Metabolism, and the Respiratory Tract