The Effect Curve of Ambient Temperature on VO2max: A Study on Optimal Cycling Temperature

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 “optimal exercise temperature and performance curve.” 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 “optimal exercise temperature and performance curve” is one of the key variables determining 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 adapt strategies 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 particularly unique: hot and humid summers, cold and damp winters, extreme altitude variation from sea level to Wuling at 3,275 meters, plus urban air pollution and typhoon season, making environmental physiology especially valuable in practice for the local sports community. This article will take you from cellular and systemic physiological mechanisms, through empirical research in top international journals, quantitative dose-response relationships, differences in responses across populations, to directly actionable training applications and Taiwan-specific scenarios, and finally debunk long-circulated myths—so that your understanding of the “optimal exercise temperature and performance curve” is truly built on science, not hearsay.

Academic Research Review

Regarding the scientific exploration of the “optimal exercise temperature and performance curve,” 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. Galloway & Maughan (1997). A classic study in Medicine & Science in Sports & Exercise, comparing cycling endurance at 4, 11, 21, and 31°C to identify the temperature yielding the best performance.

2. Ely et al. (2007). Used marathon performance big data in Medicine & Science in Sports & Exercise to map the relationship curve between air temperature and performance.

3. Vanos et al. (2020). Integrated environmental parameters and exercise performance into a multivariate model in Temperature.

4. Périard et al. (2021). A comprehensive review in Physiological Reviews of the integrated mechanisms of environmental heat on exercise performance.

Taken together, these studies show that the scientific picture of the “optimal exercise temperature and performance curve” has been continuously refined as measurement techniques have advanced. Early studies mostly manipulated temperature, humidity, or partial pressure of oxygen in environmental chambers, observing changes in maximal oxygen uptake, 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 experimental and control conditions, 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 the average amateur. When interpreting “statistical significance” and “effect size,” we must also distinguish between average trends in the laboratory and practical meaning on an individual race course—a 3% performance difference may determine rankings in elite competition, while its significance for a recreational rider is relatively limited. It is precisely this careful attention to levels of evidence and scope of applicability that forms the foundation of scientific training.

Core Mechanisms

The relationship between environmental temperature and endurance performance follows an inverted U-shaped curve: both excessive cold and excessive heat are detrimental, with an optimal “sweet spot” in between. Classic research shows that the optimal environmental temperature for prolonged endurance cycling is approximately 10 to 15°C—a temperature that is sufficient to maintain muscle warmth and normal metabolism while effectively dissipating heat and preventing excessive core temperature rise. Below this range, muscle temperature drops, warm-up requirements increase, and metabolic efficiency declines slightly; above this range, heat dissipation load rises, competition for skin blood flow intensifies, cardiovascular drift appears, and performance declines as temperature rises, with the magnitude of decline amplified by longer exercise duration. This curve is also modulated by exercise duration, intensity, wind speed, and individual acclimatization status: short-duration, high-intensity efforts are less sensitive to heat, while prolonged endurance is highly sensitive to temperature.

To truly understand how the “optimal exercise temperature and performance curve” affects exercise 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—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 Exercise 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 |

Special emphasis should be placed on the two dimensions of “dose-response” and “temporal dynamics.” The same environmental exposure can produce vastly different or even opposite effects under different intensities, durations, and acclimatization states—this is precisely why many popular recommendations are one-sided. The limiting factors of exercise performance also shift dynamically with context: for short-duration, high-intensity efforts, limitations mostly arise from anaerobic energy supply and local metabolism, while for multi-hour endurance events, the focus shifts to the combined effects of rising core temperature, fluid imbalance, glycogen depletion, and central fatigue. The “optimal exercise temperature and performance curve” deserves in-depth exploration precisely because it can selectively influence 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 scenarios such as heat, cold, high altitude, or pollution—and 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 of the “optimal exercise temperature and performance curve,” serving as the most important quantitative reference when designing training and race preparation plans:

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

|—|—|—|

| <5°C | Too cold | Low muscle temperature, high warm-up demand |

| 10–15°C | Optimal zone | Peak performance |

| 21°C | Mildly warm | Slight decline but acceptable |

| >31°C | Significantly warm | Marked performance decline |

From 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 no additional benefits—only sharply rising risks and costs. This means that “finding your own optimal exposure” matters far more than “chasing extremes at all costs.” Whether it’s the daily heat dose for heat adaptation, the altitude and duration of high-altitude training, or exposure time in cold environments, there exists 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 the finish line; 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 “optimal exercise temperature and performance curve” is not equal for everyone. Age, sex, training status, body type, adaptation state, and genetic background all significantly modulate an individual’s magnitude of response to the environment. Applying a one-size-fits-all recommendation while ignoring these differences is one of the most common errors in applied environmental physiology.

| Population Aspect | Response Characteristics | Practical Recommendations |

|—|—|—|

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

| Male vs. Female | Differences in body surface area-to-mass ratio, hormonal cycles, and sweat composition | Females should undergo individualized assessment of heat dissipation and hydration, while monitoring 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 require 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 faster—each carries distinct risks |

When interpreting individual differences, one must also be wary of a statistical trap: studies typically report “group mean responses,” but beneath the average often lies enormous individual variability. In the same environmental intervention, some may be strong responders, others 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 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 sensation, 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 young elites. When facing hot-humid summers 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 how the menstrual cycle affects baseline core temperature and fluid regulation, as well as whether energy availability is sufficient. Once you understand population differences, you’ll realize: truly professional environmental physiology advice is always an individualized prescription that is “case by case,” never a one-size-fits-all slogan.

Practical Training Applications

Theory must ultimately translate into training plans and race courses. Below is a practical framework for converting the “optimal exercise temperature and performance curve” into concrete training and race 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 it’s 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 event-specific environmental adaptation 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 overexposure.

• 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, you can rehearse different environmental scenarios across key midweek sessions and weekend long rides: high-intensity days focus on maintaining power quality in the target environment and testing cooling or insulation gear; long-distance days emphasize hydration and sodium pacing, thermoregulation, and long-duration gear tolerance. Through repeated rehearsal, your 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 “only taking the environment seriously on race day while treating everyday training casually”—this is precisely putting the cart before the horse. Everyday training is the ideal laboratory for building heat tolerance, testing hydration doses, familiarizing yourself with gear, and cultivating environmental coping 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 in the environment”—heat or altitude slows recovery and compounds fatigue accumulation. The quality of recovery between consecutive training days often determines whether you can steadily accumulate training load without injury, and training load 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—both your progress and your safety will be noticeably different.

Local Applications in Taiwan

Taiwan’s unique climate, terrain, and race culture add a distinct local flavor to the application of the “optimal exercise temperature and performance curve.” In summer, high temperature and humidity mean perceived temperatures often exceed 35°C with relative humidity frequently above 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 wind chill, while mountainous areas may present hypothermia risks. 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 West-to-East Wuling climb, the Hualien–Taitung Cycling Tour, Sun Moon Lake loop, Taroko Marathon, various triathlons, and round-island challenges as examples, athletes should factor local and seasonal environmental conditions into their planning: summer races 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 races require enhanced windproofing, warmth, and hypothermia protection. Make good use of the Central Weather Administration’s forecasts for perceived temperature, humidity, wind speed, and air quality, converting them into daily environmental risk and strategy assessments—only then can you balance safety and optimal performance in Taiwan’s varied and demanding environment.

Common Myth-Busting

Myth: “The cooler it is, the better you perform.” Being too cold is equally detrimental—muscle power and metabolic efficiency decline; the sweet spot for endurance performance is around 10 to 15°C, not colder-is-better.

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 notions fail to hold up under controlled environmental-chamber experiments and epidemiological investigations. Environmental physiology in particular is rife with oversimplified claims that compress complex dosages, timing, individual differences, and risks into a single slogan. The next time you hear a categorical environmental recommendation, it’s worth asking: “What is the level of evidence behind this claim? Who is the target audience? Are the dosage, 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 optimal exercise temperature and performance curve” 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 exercise performance is real and profound—but by no means unmanageable. The key lies in understanding the mechanisms, mastering the dosage, individualizing adjustments, and coordinating with overall training, recovery, and nutrition. For endurance 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 round-island route protect themselves, push their limits, and enjoy the purest joy of sport through the wisdom of environmental physiology—amid heat, cold, high altitude, and all kinds of challenges. 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

• Physiological Responses to Cold-Weather Cycling: Research on Vasoconstriction, Muscle Metabolism, and the Respiratory Tract
• The Impact of Climate Change on Taiwan’s Cycling Events: A Physiological Prediction Study on Rising Temperatures
• Quantifying the Suppression of VO2max by Taiwan’s Summer Heat and Humidity: An Environmental Physiology Study
• Differences in Exercise Performance Between Maritime and Continental Climates: A Taiwan Case Study