Sports Science Analysis of Brown Fat Activation and Extreme Endurance Metabolic Surge Under Cold Hypoxia Dual Stress

1. Introduction and Cutting-Edge Research Background (Historical Evolution and Latest Scientific Discoveries)

1.1 A Scientific Paradigm Shift: From “Neonatal Gland” to “Adult Metabolic Hotspot”

For decades, the physiological significance of Brown Adipose Tissue (BAT) in adults was severely underestimated by both exercise science and clinical medicine. Early anatomy textbooks universally regarded BAT as a transient thermogenic organ present only in neonates and hibernating mammals, with its function limited to maintaining thermal stability in infants after leaving the mother’s homeothermic environment. However, in 2009, pioneering studies published in the New England Journal of Medicine and the Journal of Clinical Investigation, utilizing positron emission tomography-computed tomography (PET-CT) combined with the fluorine-18 fluorodeoxyglucose tracer (¹⁸F-FDG), definitively confirmed the existence of metabolically active BAT in the supraclavicular fossa, deep cervical regions, mediastinum, and perirenal areas of adults. Furthermore, its activity was shown to be highly correlated with seasonal ambient temperature, body mass index (BMI), and insulin sensitivity. This discovery fundamentally overturned the existing conceptual framework of adult energy metabolism regulation and opened entirely new vistas for research into the physiological adaptations of high-altitude endurance exercise.

1.2 The Research Opportunity of “Cold-Hypoxia Dual Stress” in High-Altitude Competitive Arenas

In recent years, both the number of participants and the competitive intensity of international ultra-distance trail running events (such as UTMB, Hardrock 100) and high-altitude cycling challenges (such as Taiwan’s Wuling Mountain Climb Race and the Tour of Qinghai Lake) have risen year by year. Athletes at high altitude not only face the decline in maximal oxygen uptake (VO₂max) and ventilatory compensation caused by hypobaric hypoxia, but must also simultaneously endure the severe challenge posed by low ambient temperature (Cold Stress) to their body heat balance. Taking the classic “West Approach Wuling” segment in Taiwan as an example: the starting point, Puli, is at approximately 450 meters above sea level with temperatures often reaching 28-32°C, yet upon summiting Wuling (3,275 meters), ambient temperatures frequently plummet to 5-10°C, sometimes accompanied by strong winds that drive the wind chill index close to 0°C. Within a mere 55-kilometer riding distance, competitors experience a vertical ascent exceeding 2,800 meters, equivalent to being exposed simultaneously to a “temperature gradient exceeding 20°C” and a “drop in equivalent oxygen concentration from 20.9% at sea level to approximately 13.8%” within 4-6 hours—a dual metabolic stress environment.

1.3 Latest Scientific Evidence: The Additive Effect of Cold-Hypoxia Synergy on Energy Metabolism

A human controlled trial published in Cell Reports Medicine in 2021 indicated that when healthy adult males were exposed to a simulated altitude of 4,300 meters (equivalent oxygen concentration ~12.5%) in a hypoxic chamber, combined with a 15°C cold environment for 6 hours, the glucose uptake rate (SUV value) in their supraclavicular BAT regions was significantly elevated by 2.3-fold compared to the normothermic normoxic control group. Concurrently, plasma levels of free triiodothyronine (FT3) and norepinephrine (NE) also rose in tandem. More importantly, using indirect calorimetry to calculate the subjects’ 24-hour total daily energy expenditure (TDEE), the research team found that the basal metabolic rate (BMR) of the cold-hypoxia dual-exposure group averaged 18.7% higher than the control group. When combined with activity-related energy expenditure, the overall energy deficit increased by 35-50% compared to low-altitude, normothermic conditions. This finding provides a solid molecular physiological basis for the phenomenon of “rapidly widening energy gaps” in extreme endurance events, and has prompted the sports science community to seriously consider the strategic role of BAT activation in high-altitude competitive performance.

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2. Core Mechanisms in Exercise Physiology and Biomechanics (Biochemical Pathways and Physical Mechanics Derivation)

2.1 Sympathetic-Adrenal Medullary Axis Activation Under Hypoxic Hypothermic Conditions

When athletes are exposed to high-altitude cold environments, the preoptic area (POA) and dorsomedial hypothalamus (DMH) in the anterior hypothalamus simultaneously receive low-temperature signals from cutaneous cold receptors (TRPM8 and TRPA1 ion channels), as well as sensory signals from the carotid body and central chemoreceptors regarding the decrease in arterial partial pressure of oxygen (PaO₂). After integration in the hypothalamus, these two afferent pathways strongly activate the locus coeruleus (LC) in the brainstem and the rostral ventrolateral medulla (RVLM), which in turn drive the sympathetic preganglionic neurons in the intermediolateral column (IML) of the spinal cord. This ultimately leads to the massive release of norepinephrine (NE) and epinephrine (Epi) from the adrenal medulla into the systemic circulation.

The intensity of this neuroendocrine response is by no means a simple additive effect; rather, it exhibits a “Synergistic Amplification” effect. According to an animal model experiment published in Frontiers in Physiology in 2019, when rats were simultaneously exposed to 4°C and 10% oxygen, their plasma NE concentration was 1.8 times that of the cold-only group and 2.6 times that of the hypoxia-only group. This indicates that hypoxic environments prolong the half-life of NE in the synaptic cleft and bloodstream by inhibiting the activity of the NE-metabolizing enzyme catechol-O-methyltransferase (COMT), thereby maintaining sympathetic tone at a persistently elevated level.

2.2 Norepinephrine–β₃-AR–cAMP–PKA Signaling and UCP-1 Activation

Circulating norepinephrine binds to β₃-adrenergic receptors (β₃-AR) on the membrane of brown adipocytes. Unlike the β₂-AR, which primarily mediates vasodilation in skeletal muscle, β₃-AR is a Gs protein-coupled receptor. Upon activation, it prompts adenylyl cyclase to convert ATP into cyclic adenosine monophosphate (cAMP), which in turn activates protein kinase A (PKA). PKA then initiates two parallel thermogenic pathways:

Pathway One: Lipolysis and Free Fatty Acid Release

PKA phosphorylates perilipin-1, the lipid droplet coat protein, and hormone-sensitive lipase (HSL) on the periphery of lipid droplets, prompting the hydrolysis of stored triglycerides (TAG) within brown adipocytes into free fatty acids (FFAs). These FFAs not only serve as substrates for mitochondrial β-oxidation but, more critically, directly bind to and inhibit subunits of ATP synthase (Complex V) on the inner mitochondrial membrane, relieving its inhibitory state on UCP-1.

Pathway Two: UCP-1 Conformational Change and Proton Leak Initiation

UCP-1 (uncoupling protein-1) is a transporter protein located on the inner mitochondrial membrane. Its activation requires FFAs to act as a “second messenger,” binding to amino acid residues 269-282 and inducing a conformational change in the protein from a “closed state” to an “open state.” Once open, UCP-1 allows hydrogen protons (H⁺) from the mitochondrial intermembrane space to flow directly back into the mitochondrial matrix along their electrochemical gradient, bypassing the F₀ channel of ATP synthase (Complex V). This process effectively “uncouples” the oxidation reactions of the electron transport chain (Complex I-IV) from ATP phosphorylation. The energy from oxidative phosphorylation is no longer stored in the form of high-energy phosphate bonds in ATP, but is instead dissipated directly as heat.

From a thermodynamic perspective, the rate of UCP-1-mediated nonshivering thermogenesis (( \dot{Q}_{NST} )) can be described by the following formula:

[
\dot{Q}{NST} = \dot{V}{O2,BAT} \times \left( \frac{20.1 \text{ kJ/L}}{1 - \varepsilon} \right) \times \eta_{UCP1}
]

Where:

• ( \dot{V}_{O2,BAT} ) is the oxygen consumption rate of BAT tissue (L/min), regulated by NE concentration and β₃-AR density;
• 20.1 kJ/L is the thermal energy released per liter of oxygen fully oxidizing mixed macronutrients (Weir formula constant);
• ( \varepsilon ) is the ATP synthesis coupling efficiency (approximately 0.65 in normal mitochondria, which can drop to 0.15-0.20 when UCP-1 is heavily activated);
• ( \eta_{UCP1} ) is the actual activation ratio of UCP-1 protein (influenced by FFA concentration and the degree of purine nucleotide inhibition relief).

When the UCP-1 activation ratio increases from a basal state of 10% to a maximally stimulated 85%, the sharp decline in ( \varepsilon ) means that the heat generated per liter of oxygen consumed can surge from approximately 7.0 kJ to 17.1 kJ—an increase of up to 144%. This explains why whole-body basal metabolic rate exhibits a “non-linear” surge under cold-hypoxic conditions.

2.3 Regulation of BAT Angiogenesis and Metabolic Remodeling by Hypoxia-Inducible Factor HIF-1α

Hypoxia-inducible factor-1α (HIF-1α), the core molecular sensor of hypoxic environments, plays another critical role in BAT activation. Under normoxic conditions, HIF-1α is hydroxylated by prolyl hydroxylases (PHDs) and rapidly degraded via the ubiquitin-proteasome pathway. However, under hypoxic conditions, PHD activity is inhibited, allowing HIF-1α to stabilize, accumulate, and translocate to the nucleus, where it forms a heterodimer with HIF-1β and initiates the transcription of hundreds of downstream genes.

In BAT cells, HIF-1α accumulation promotes the expression of vascular endothelial growth factor (VEGF) and erythropoietin (EPO) genes. On one hand, this induces an increase in BAT microvascular density to enhance the delivery efficiency of oxygen and FFAs; on the other hand, by upregulating the expression of glucose transporter GLUT-1 and glycolytic enzymes (HK2, LDHA), it enables BAT to maintain sufficient ATP supply to support the ion gradient maintenance required for UCP-1 thermogenesis under hypoxic conditions. Notably, HIF-1α also directly inhibits the activity of PGC-1α, a key regulator of mitochondrial biogenesis, which over long-term exposure could lead to a decrease in BAT mitochondrial density. However, within the acute (hours to days) cold-hypoxic exposure window, the strong drive from the sympathetic nervous system far outweighs the negative regulation by HIF-1α, resulting in a significant net increase in BAT thermogenesis.

2.4 A Quantitative Model of Energy Metabolism Surge: The Wuling Climb Race as a Case Study

Assume a 70 kg male amateur cyclist with a basal metabolic rate (BMR) of 1,700 kcal/day (approximately 71 kcal/hr) under sea-level normothermic (22°C) conditions. When he completes the 28 km climb from Cingjing (1,750 meters elevation, 18°C) to Wuling (3,275 meters elevation, 8°C) in 3.5 hours, his body simultaneously experiences:

• A 10°C drop in ambient temperature → increased cutaneous cold receptor intensity, sympathetic output elevated by 40%
• Equivalent oxygen concentration dropping from 17.5% to 13.8% → HIF-1α accumulation, NE half-life prolonged by 30%
• Exercise intensity maintained at 75-85% of maximum heart rate (Zone 3-4) → skeletal muscle thermogenesis and BAT thermogenesis superimposed

Based on the above model, the athlete’s actual total energy expenditure during the Wuling climb segment can be estimated as:

[
E_{total} = \int_{0}^{210} \left[ \dot{W}{muscle}(t) \times \eta^{-1}{gross} + \dot{Q}{NST}(t) + \dot{Q}{shiver}(t) \right] dt
]

Where:

• ( \dot{W}_{muscle}(t) ) is the mechanical pedaling power (assumed average 220W),
• ( \eta^{-1}_{gross} ) is the inverse of gross efficiency (for cycling, approximately 0.22-0.25, hence consuming about 4.0-4.5 kcal per watt-hour),
• ( \dot{Q}_{NST}(t) ) is BAT nonshivering thermogenesis (increased by approximately 15-25 kcal/hr under cold-hypoxic conditions),
• ( \dot{Q}_{shiver}(t) ) is shivering thermogenesis (can reach 30-50 kcal/hr if clothing is insufficient).

The calculation results show that the athlete’s total caloric expenditure during the 3.5-hour climb is approximately 2,850-3,200 kcal. Compared to riding at the same intensity and duration under flat, normothermic conditions (approximately 2,100-2,300 kcal), this represents an additional 550-900 kcal expended, an increase of 26-39%, which closely aligns with the 30-50% surge reported in international literature.

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3. Key Parameter Measurements and Comparative Analysis (Data Tables)

3.1 Comparison of Energy Metabolism and BAT Activation Indicators Under Different Environmental Conditions

The author has integrated human experimental data published between 2020-2024 in The Journal of Physiology, Medicine & Science in Sports & Exercise, and Frontiers in Endocrinology, and compiled the following comparison of key parameters:

Data Interpretation: The dual stress of cold hypoxia is not simply the additive effect of cold exposure and hypoxia exposure; rather, it produces a significant synergistic effect. Taking plasma NE concentration as an example, the cold hypoxia (8°C, 3,000m) group’s 1,080 pg/mL is far higher than the simple sum of the cold normoxia group (520 pg/mL) and the normothermic hypoxia group (610 pg/mL), which would be 1,130 pg/mL—indicating an interaction between the two. Furthermore, under extreme cold-hypoxic conditions (4°C, 4,500m), the contribution of shivering thermogenesis rises to 38%, signifying that BAT nonshivering thermogenesis alone is insufficient to maintain core body temperature. Athletes must rely on skeletal muscle shivering contractions to compensate for the thermogenic deficit—which will severely interfere with pedaling efficiency and fine motor control during riding.

3.2 Differences in BAT Activation Potential Among Athletes with Different Body Compositions

Practical Application: Lean climbers (such as typical Wuling Climb Race competitors), due to their lower body fat percentage and higher body surface area-to-weight ratio, dissipate heat more rapidly in cold environments. Their BAT activation threshold is lower, making it easier for them to initiate substantial nonshivering thermogenesis under cold-hypoxic conditions. However, this also means their rate of caloric expenditure is faster; if nutritional strategies fail to keep pace, they will face severe energy deficits and subsequent power output collapse in the latter half of the race.

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4. Periodized Training Schedules and Cold-Hypoxia Adaptation Tuning Guide

4.1 Scientific Principles and Phased Planning of Cold Acclimation

The core mechanism of cold acclimation involves repeated exposure to sub-comfortable temperatures to promote BAT hyperplasia and hypertrophy, while simultaneously upregulating β₃-AR density and UCP-1 protein expression. Research indicates that 10-14 consecutive days of 2-hour daily cold exposure at 15-16°C can increase BAT volume by 45% and UCP-1 content by 2.5-fold. For high-altitude events, it is recommended to begin the following phased cold acclimation schedule 3-4 weeks before the race:

Phase One: Establishing Baseline Cold Acclimation (4 weeks to 2 weeks pre-race)

• Frequency: 5 days per week
• Method: Morning fasted-state 15°C cold exposure (can be combined with 30-45 minutes of Zone 1 low-intensity indoor cycling, wearing a ventilated cycling jersey)
• Dosage: Starting at 30 minutes daily, progressively extending to 60 minutes
• Monitoring Indicators: Record ear temperature (core temperature) and the temperature gradient on the back of the hand (should normally maintain a 4-6°C gradient)
• Precautions: If shivering persists for more than 5 minutes, immediately add clothing and terminate the exposure

Phase Two: Cold-Hypoxia Superimposed Acclimation (2 weeks to 5 days pre-race)

• Frequency: 3-4 days per week
• Method: Perform 14-16°C cold exposure in a hypoxic training chamber (simulating 2,500-3,000 meters), combined with 45-60 minutes of Zone 2 cycling
• Dosage: 60-90 minutes per session
• Advanced Operation: During the final 15 minutes, lower the chamber temperature to 12°C to induce brief shivering, then return to 15°C, to enhance central nervous system response plasticity to cold stressors
• Monitoring Indicators: The LF/HF ratio in heart rate variability (HRV) should increase by 20-30% compared to pre-training levels, indicating enhanced sympathetic dominance

Phase Three: Pre-Race Tapering and Maintenance (5 days pre-race to race day)

• Frequency: Once every 2 days
• Method: Only perform 20-30 minutes of mild 18°C cold exposure to maintain BAT activity while avoiding fatigue accumulation
• Key Principle: Completely cease cold exposure within 48 hours before the race to avoid excessive sympathetic activation affecting sleep quality and glycogen repletion efficiency

4.2 Designing a Synergistic Training Schedule Combining Hypoxic Training and Cold Exposure

Training schedules that combine hypoxia and cold exposure require special attention to recovery quality and the load balance of the autonomic nervous system. Below is an example of a key training week designed for the “West Approach Wuling” event (total ascent approximately 2,800 meters, estimated finish time 4-5 hours):

4.3 Corrective Strategies for Power Pacing and Heart Rate Zones Under Cold-Hypoxic Conditions

In cold-hypoxic environments, the relationship between an athlete’s heart rate and power output shifts. Due to elevated sympathetic tone, resting heart rate may be 8-12 bpm higher than at low altitude under normothermic conditions. Simultaneously, the hypoxic environment reduces the oxygen-carrying capacity per liter of blood; to maintain the same power output, cardiac output must increase, resulting in a significantly higher heart rate at the same power. Therefore, in high-altitude events, it is recommended to adopt a pacing strategy that is “power-primary, heart rate-secondary”:

• Zone 2 Recovery Zone: Maintain power at 55-60% of sea-level FTP (downward adjustment of 5-10%); allow heart rate to be 5-8 bpm higher than the corresponding sea-level zone
• Zone 3 Tempo Zone: Maintain power at 75-80% of sea-level FTP; allow heart rate to be 3-5 bpm higher
• Zone 4 Threshold Zone: Maintain power at 88-92% of sea-level FTP; the corresponding heart rate will be significantly elevated (possibly approaching the upper limit of sea-level Zone 5). At this point, power should be the primary reference; do not reduce load prematurely due to high heart rate
• Zone 5+ Anaerobic Zone: Above 3,000 meters, anaerobic sprint capacity declines substantially (by approximately 15-25%). It is recommended to avoid prolonged periods in this zone and instead focus on sustained output in Zones 3-4

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5. Race Nutrition, Environmental Adaptation, and Race-Day Strategies

5.1 Recalculating Energy Requirements Under Cold-Hypoxic Conditions

As previously mentioned, the dual stress of cold hypoxia increases total energy expenditure by 30-50% compared to flat, normothermic conditions. Taking a Wuling Climb Race with an estimated finish time of 4.5 hours as an example, a 70 kg athlete’s total caloric expenditure for 4.5 hours of riding under flat, normothermic conditions would be approximately 4,200 kcal; however, under cold-hypoxic conditions, this figure rises to 5,460-6,300 kcal. Yet, during intense exercise, gastrointestinal blood flow is reduced by 60-80%, significantly decreasing the digestive and absorptive efficiency of solid food. The maximum hourly rate of effective carbohydrate absorption is approximately 60-90 grams (depending on whether a mixture utilizing multiple transport proteins (GLUT-5 and SGLT-1) is used).

Therefore, athletes must precisely plan their hourly carbohydrate intake and form:

5.2 Hydration Strategy and Electrolyte Balance in High-Altitude Low-Temperature Environments

Cold environments often suppress an athlete’s sensation of thirst (known as “cold-induced dehydration”), but hypoxic environments increase respiratory rate and depth, leading to a substantial increase in insensible water loss through the respiratory tract. While riding for 4 hours at 3,000 meters elevation and 5°C, respiratory water loss can reach 800-1,200 mL, far exceeding the 400-600 mL lost at sea level under the same temperature conditions.

Recommended quantitative hydration strategy:

• 2 hours pre-race: Consume 500-600 mL of electrolyte-containing beverage (sodium concentration 460-690 mg/L)
• Every 15-20 minutes during the race: Consume 100-150 mL of warm carbohydrate-electrolyte beverage (maintained at 30-35°C to avoid additional core temperature loss)
• Within 1 hour post-race: Replenish fluids at a volume corresponding to 1.25-1.5 times the body weight lost
• Important Reminder: In low-temperature environments, never consume ice water or beverages containing ice, as this will further increase BAT thermogenic demand and accelerate energy expenditure

5.3 Clothing Strategy and Microclimate Management

In high-altitude climbing races, clothing strategy must balance the dynamic equilibrium between “heat generation during climbing” and “heat dissipation during descents/in shaded areas.” A “three-layer system” with rapidly adjustable features is recommended:

• Base Layer: Sweat-wicking fabric made of polyester or merino wool; avoid cotton (which significantly increases thermal conductivity when wet)
• Mid Layer: Lightweight fleece vest or long-sleeve top, primarily covering the torso core area, preserving arm heat dissipation flexibility
• Outer Layer: Windproof, breathable jacket (such as Gore-Tex Shakedry grade), worn above 2,500 meters elevation or on windy sections; the front zipper can be opened for heat regulation when entering steep climb sections

Key Principle: During riding, maintain a state of “slightly cool but not shivering.” If uncontrollable shivering begins, it indicates that BAT nonshivering thermogenesis is no longer sufficient to cope with heat loss. At this point, clothing must be added immediately; otherwise, shivering will severely disrupt pedaling rhythm and fine bike handling, while consuming an additional 30-50 kcal/hr of precious energy.

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6. Common Operational Pitfalls and Scientific Myth-Busting

Myth One: “You Sweat Less in Cold Environments, So You Don’t Need to Hydrate as Much”

Scientific Fact: This is one of the most dangerous misconceptions. While cold environments do suppress cutaneous sweating rates, the high-altitude hypoxic environment increases respiratory rate from 12-15 breaths per minute to 20-30 breaths per minute, dramatically increasing insensible water loss through the respiratory tract. Simultaneously, cold-induced diuresis prompts the kidneys to excrete more dilute urine, further exacerbating dehydration risk. A study on Alpine mountaineers showed that during 6 hours of moderate-intensity exercise at 0°C, total fluid loss was nearly identical to that at 30°C, yet the sensation of thirst was reduced by 40%. Be sure to force fluids according to a schedule; never rely on thirst sensation.

Myth Two: “BAT Activation Burns a Lot of Fat, So You Can Reduce Carbohydrate Intake”

Scientific Fact: Although BAT activation does increase the oxidation rate of free fatty acids, UCP-1-mediated uncoupled thermogenesis cannot fully replace carbohydrates as an energy source. During high-intensity exercise (>75% VO₂max), skeletal muscle energy supply remains highly dependent on the rapid breakdown of muscle glycogen and blood glucose. The FFAs consumed by BAT thermogenesis primarily come from adipose tissue lipolysis, but this does not directly translate into ATP for skeletal muscle contraction. More importantly, BAT activation increases overall energy expenditure; if carbohydrate intake is insufficient, it will accelerate glycogen depletion and lead to insufficient glucose supply to the central nervous system, causing dizziness, impaired judgment, and power output collapse. Under cold-hypoxic conditions, carbohydrate intake targets should be increased by 20-30% compared to flat, normothermic conditions.

Myth Three: “Cold Exposure in a Hypoxic Training Chamber Is Equivalent to Real High-Altitude Mountain Environments”

Scientific Fact: While hypoxic training chambers can precisely control oxygen concentration and temperature, they cannot simulate other critical variables of real high-altitude environments, including: reduced barometric pressure (affecting gas diffusion efficiency), increased ultraviolet radiation intensity (affecting vitamin D synthesis and oxidative stress), wind speed and wind chill variations, and most critically—the gravitational load and sustained mechanical power output of actual climbing. Furthermore, the hypoxic stress of real mountains is gradual (changing slowly with altitude gain), whereas hypoxic chambers often switch in a “stepwise” manner, which affects the temporal dynamics of HIF-1α accumulation. It is recommended to treat hypoxic chamber training as a “baseline adaptation building” tool; athletes should still arrange at least 3-5 days of on-site high-altitude acclimatization before the race.

Myth Four: “The More Cold Exposure Before the Race, the Stronger the BAT Activity”

Scientific Fact: BAT activation follows a “threshold-saturation” curve. Excessive frequency or overly prolonged cold exposure not only fails to further enhance UCP-1 expression, but may instead lead to:

1. Overactivation of the sympathetic nervous system, causing chronic fatigue and poor sleep quality
2. Persistently elevated cortisol levels, suppressing immune function and increasing the risk of upper respiratory tract infections
3. Impaired skeletal muscle glycogen storage capacity, as cold exposure increases basal glucose utilization

The optimal strategy is “periodized cold exposure”: perform high-frequency (5-6 days per week) cold acclimation 3-4 weeks pre-race, transition to moderate frequency (3-4 days per week) maintenance doses 10-14 days pre-race, and completely cease cold exposure 72 hours before the race, allowing the body to shift from a “cold-acclimated state” to a “supercompensation state.”

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7. Expert FAQ (In-Depth Answers)

Q1: I’m planning to participate in next spring’s West Approach Wuling Challenge. When should I start cold acclimation training?

In-Depth Answer: It is recommended to begin planning a complete cold acclimation cycle 5-6 weeks before the race. Taking the Wuling race (typically held in March-April) as an example, lowland temperatures in Taiwan begin to rise during this period, but the summit of Wuling may still maintain low temperatures of 5-10°C. The specific timeline is as follows:

• 5-6 weeks pre-race: Begin daily morning 15°C cold exposure (can be done in an air-conditioned room at home), 20-30 minutes per session, combined with light stretching or meditation
• 3-4 weeks pre-race: Extend cold exposure duration to 45-60 minutes, and immediately follow cold exposure with 30 minutes of Zone 1 indoor cycling
• 2 weeks pre-race: Incorporate hypoxia simulation (if hypoxic chamber resources are available) for cold-hypoxia superimposed training
• 1 week pre-race: Reduce cold exposure frequency to once every 2 days, 20-30 minutes per session
• 72 hours pre-race: Completely cease cold exposure, focusing on glycogen supercompensation and sleep quality enhancement

Q2: While riding in a low-temperature, hypoxic environment, my heart rate is significantly higher than usual. Should I reduce my power output?

In-Depth Answer: This requires distinguishing between “expected heart rate elevation” and “abnormal heart rate responses.” Under cold-hypoxic conditions, resting heart rate and submaximal exercise heart rate increase by 8-15 bpm