Cycling Physiology During Taiwan's Southwesterly Flow (Plum Rain) Season: A Study on the Unique Challenges of High Humidity

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 challenge of heat dissipation in high-humidity environments.” It also integrates 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 challenge of heat dissipation in high-humidity environments” 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 knows how to adjust their strategy to the environment is often the one who can maintain pace in the latter stages of a race and avoid collapse or mishaps. Taiwan’s geography is especially unique: hot and humid summers, cold and damp winters, extreme altitude gains from sea level to the 3,275-meter Wuling, plus urban air pollution and typhoon season, making environmental physiology particularly valuable in practice for the local sports community. This article will take you from the physiological mechanisms at the cellular and systemic levels, through empirical research in top international journals, the 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-circulated myths, so that your understanding of “the challenge of heat dissipation in high-humidity environments” is truly built on science, not hearsay.

Review of Academic Research

Regarding the scientific exploration of “the challenge of heat dissipation in high-humidity environments,” 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. Maughan, Otani & Watson (2012). European Journal of Applied Physiology compared body temperature and performance during exercise under different humidity levels, confirming that high humidity significantly accelerates the rise in core body temperature.

2. Che Muhamed et al. (2016). Journal of Sports Sciences quantified the suppression of time-trial performance by high humidity in tropical heat-acclimatized subjects.

3. Wingo, Ganio & Cureton (2012). Exercise and Sport Sciences Reviews explained performance decline under high heat and humidity through cardiovascular drift.

4. Sawka, Cheuvront & Kenefick (2012). Comprehensive Physiology reviewed fluid and thermoregulation in high-humidity environments.

Looking at these studies as a whole, the scientific picture of “the challenge of heat dissipation in high-humidity environments” has deepened as measurement techniques have advanced. Early studies mostly 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 use randomized crossover designs, where each subject serves as their own control, greatly reducing the noise of individual differences. However, extrapolating conclusions must still be done cautiously: a single environmental variable controlled in the lab does not necessarily equal the complex combination of heat, humidity, wind, radiation, and fatigue on a real race course; nor do the responses of well-trained subjects necessarily apply to the average amateur. When interpreting “statistical significance” and “effect sizes,” we must also distinguish between the average trend in the lab and the practical meaning for an individual on the course—a 3% performance difference may decide a placing in elite competition, but its significance for a recreational rider is relatively limited. It is precisely this careful attention to the level of evidence and the scope of applicability that forms the foundation of scientific training.

Core Mechanisms

Humidity is the invisible killer of heat dissipation. The primary route of heat loss in high temperatures is sweat evaporation, with each gram of sweat evaporating carrying away approximately 0.58 kilocalories of heat. But the evaporation rate depends on the water vapor pressure gradient between the skin and the air. When relative humidity rises and the air approaches saturation, this gradient shrinks, sweat cannot evaporate and simply drips off, and heat dissipation efficiency drops dramatically. During the plum rain season, the southwest monsoon brings high temperatures with relative humidity often exceeding 85%. Even if the temperature is not extreme, the perceived and physiological load is very heavy. The body can only rely on increasing skin blood flow to dissipate heat, leading to cardiovascular drift, a continuously rising core temperature, and a forced reduction in pace. High humidity also makes sweating appear to increase while providing no effective cooling, accelerating dehydration.

To truly understand how “the challenge of heat dissipation in high-humidity environments” 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, disrupting heat dissipation and fluid balance, or altering central fatigue perception and exercise drive. The table below summarizes the key effects of this topic at different physiological levels to help you build a complete mechanistic picture:

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

|—|—|—|

| Cardiovascular System | Affects blood flow distribution, stroke volume, and circulating 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 | Regulates fatigue perception, exercise drive, and cognitive decision-making | Affects “how tired it feels,” the ability to persevere, and safety judgments |

Two dimensions deserve special emphasis: “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 exercise performance also shift dynamically with context: for short, high-intensity efforts, the limits come mostly 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 challenge of heat dissipation in high-humidity environments” is worth deep exploration precisely because it can specifically target some of these limiting factors. Only by understanding the mechanisms can we judge “how to adjust for a given environment, by how much, and when,” rather than being dragged along 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 adjust 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. Too little environmental stimulus fails to reach the physiological threshold, producing no adaptation or effect; excessive exposure can 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 challenge of heat dissipation in high-humidity environments” and serves as the most important quantitative reference when designing training and race-preparation plans:

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

|—|—|—|

| Below 60% RH | Evaporative heat dissipation works smoothly | High intensity can be maintained |

| 70% RH | Evaporation efficiency declines | Heart rate drift appears |

| Above 85% RH (typical of plum rain season) | Evaporation severely impaired | Intensity must be significantly reduced |

| Near saturation + high temperature | Heat dissipation nearly ceases | High risk of heat injury |

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, there are no additional benefits, and 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 of 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: the lab average is a starting point, not an endpoint; everyone’s body size, sweat rate, acclimatization level, and genetic background cause the optimal dose to shift individually. Only by calibrating with your own data can you turn population science into a personal prescription.

Differences Across Populations

The impact of “the challenge of heat dissipation in high-humidity environments” 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 mistakes in the application of environmental physiology.

| Population Dimension | Response Characteristics | Practical Recommendations |

|—|—|—|

| Beginners vs. Advanced Athletes | Advanced athletes have more mature environmental adaptation and better tolerance, but less marginal room for adaptation | Beginners should progress conservatively, building basic tolerance before adding 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 more caution and longer adaptation |

| 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 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 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 (such as pre-cooling or heat acclimation), compare power, core temperature, heart rate, and perceived sensation, and repeat several times before drawing conclusions.

Taking the common amateur endurance population in Taiwan as an example, many are middle-aged cyclists and runners over 35 who train around their work schedules. This group’s thermoregulation and recovery capacity are already somewhat inferior to young elites. When facing hot, humid summers and high-altitude challenges, correct environmental strategies (heat acclimation, 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 that truly professional environmental physiology advice is always an individualized prescription that varies from person to person, not a universal slogan.

Practical Training Applications

Theory must ultimately translate into training plans and race courses. Below is a practical framework for turning “the challenge of heat dissipation in high-humidity environments” into concrete training and competition operations:

• Pre-race environmental rehearsal: All environmental strategies must be rehearsed 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 in the base phase, and conduct sport-specific environmental adaptation in the pre-race phase targeting the temperature, humidity, or altitude of your goal event.

• Progressive exposure: Start with mild environmental stimuli and gradually increase the load based on your body’s 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 output, 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 flaws in training design.

Using a one-week training schedule as an example, you can rehearse different environmental scenarios in key midweek sessions and the weekend long ride: 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 intake pacing, thermoregulation, and long-duration gear tolerance. 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 exactly 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 your rhythm for environmental responses.

It is recommended to integrate an environment log with your training log, recording the temperature, humidity, altitude, wind conditions, environmental strategies used, body 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. Furthermore, don’t overlook the often-underestimated aspect of “recovery in the environment”—high heat or high altitude delays 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, and both your progress and safety will be noticeably different.

Taiwan-Specific Applications

Taiwan’s unique climate, terrain, and race culture add a distinct local flavor to the application of “the challenge of heat dissipation in high-humidity environments.” In summer, high temperatures and humidity mean the perceived temperature often exceeds 35°C and relative humidity frequently tops 80%, making evaporative cooling inefficient and sweat and electrolyte losses far greater than the scenarios studied in 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 pose risks of low temperatures and hypothermia. Meanwhile, the extreme altitude gain from sea level to 3,275 meters at Wuling puts the physiological challenges of high altitude right at your doorstep.

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

Debunking Common Myths

Myth: “If the temperature isn’t high, it’s safe.” In a high-humidity environment, even at just 30°C, the physiological load can exceed that of dry heat at 35°C because evaporative cooling fails; risk should be judged by wet-bulb temperature or WBGT, not by air temperature alone.

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 in testing intuition with rigorous evidence: many seemingly obvious environmental beliefs do not hold up under controlled environmental chamber experiments and epidemiological investigations. The field of environmental physiology is especially full of oversimplified claims that compress complex doses, timing, individual differences, and risks into a single slogan. The next time you hear a dogmatic 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 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 injury.

Conclusion

“The challenge of heat dissipation in high-humidity environments” is a topic in environmental physiology that combines theoretical depth with practical value. As the evidence from international journals 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 doses, individualizing adjustments, and coordinating with overall training, recovery, and nutrition. For endurance sports enthusiasts in Taiwan, while grasping the scientific principles, it is even more important to combine them with the local hot-humid climate, extreme altitude, and changeable weather, transforming general rules into personalized prescriptions that suit you. May every cyclist and runner sweating on Wuling, in the rift valley, or on the round-island route use 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 opponent, besides the clock, is the entire environment beneath your feet and all around you.

Related Reading

• The Impact of Environmental Humidity on Running Economy: Quantifying the Increased Energy Cost of High Humidity
• Quantifying the Suppression of VO2max by Taiwan’s Summer Heat and Humidity: Environmental Physiology Research
• Cycling Conditions During Taiwan’s Northeast Monsoon: Physiological Effects of Low Temperature and Wind Chill
• Physiological Responses to Cold-Weather Cycling: Research on Vasoconstriction, Muscle Metabolism, and the Respiratory Tract