Heat Training VO₂ Max Testing

Cardiovascular Stress

Heat increases cardiovascular demand beyond the work of exercise alone:

• • Blood diverted to skin for cooling reduces blood to working muscles
• • Heart rate increases 10-20 bpm at same pace/power
• • Stroke volume decreases due to reduced blood volume
• • Cardiac output must increase to maintain performance
• • VO₂ max effectively decreases 5-15% in heat

Metabolic Changes

Heat alters substrate utilization and energy systems:

• • Increased reliance on carbohydrate vs. fat
• • Higher lactate production at submaximal intensities
• • Glycogen depletion occurs faster
• • Ventilatory thresholds shift to lower absolute workloads
• • Perceived exertion increases at same objective intensity

Thermoregulation Limits

Core temperature becomes limiting factor:

• • Core temp rises ~1°C per hour of exercise in heat
• • Performance declines when core temp exceeds 39-40°C
• • Sweat rates increase (1-2+ liters/hour)
• • Dehydration compounds cardiovascular stress
• • Heat exhaustion/stroke risk increases

Performance Decrements

Typical performance losses in heat (unacclimated):

• • Marathon: 2-5% slower per 10°F above 60°F
• • Half marathon: 1-3% slower in heat
• • 10K and shorter: Minimal impact if well-hydrated
• • Ironman: 5-10% slower in hot conditions
• • Heat acclimation reduces these decrements by 50-75%

Establish True Fitness Level

Test in cool conditions to measure actual VO₂ max without heat stress:

• • Baseline VO₂ max in optimal conditions
• • True VT1 and VT2 thresholds
• • Maximum heart rate without heat interference
• • Reference point for tracking fitness changes
• • Distinguish fitness improvements from heat adaptation

Set Training Zones for Heat Workouts

Use baseline zones to guide heat training intensity:

• • Expect heart rate 10-20 bpm higher in heat at same pace
• • Adjust pace to maintain target heart rate zones
• • Zone 2 in heat = slower pace than cool conditions
• • Accept slower paces during heat acclimation period
• • Focus on heart rate, not pace, during heat training

Track Adaptation Progress

Retest after heat acclimation to assess changes:

• • Compare pre- and post-acclimation VO₂ max
• • Assess if fitness maintained during heat training
• • Verify cardiovascular adaptations occurred
• • Adjust zones for race-specific conditions
• • Confirm readiness for hot weather racing

Traditional Heat Acclimation (2 weeks)

Protocol: Train in heat 60-90 minutes daily for 10-14 days

• • Days 1-3: Easy intensity (Zone 1-2), 60 minutes in heat
• • Days 4-7: Moderate intensity (Zone 2-3), 75 minutes
• • Days 8-14: Include some Zone 3-4 work, 90 minutes
• • Environment: 85-95°F, 40-60% humidity
• • Adaptations: Increased plasma volume, earlier sweating, lower core temp

Short-Term Acclimation (5-7 days)

Protocol: Higher intensity, shorter duration for time-constrained athletes

• • Days 1-2: 45-60 minutes Zone 2-3 in heat
• • Days 3-5: 60 minutes with Zone 3-4 intervals
• • Days 6-7: Race-specific intensity practice
• • Environment: 90-100°F for accelerated adaptation
• • Note: 60-70% as effective as traditional protocol

Passive Heat Exposure (Alternative)

Protocol: Sauna or hot bath post-workout

• • Immediately after training: 20-30 minutes sauna (170-190°F)
• • Or: 30-40 minutes hot bath (104-106°F)
• • Frequency: 4-7x per week for 2-3 weeks
• • Benefits: Plasma volume expansion, heat shock proteins
• • Advantage: Doesn't compromise training quality

Heart Rate-Based Training

Use heart rate zones from cool-condition testing, accept slower paces in heat:

• • Zone 2 easy run: Same HR as cool conditions, pace 30-60 sec/mile slower
• • Zone 3 tempo: Same HR target, pace 20-40 sec/mile slower
• • Zone 4 threshold: Same HR, pace 15-30 sec/mile slower
• • Zone 5 intervals: Shorten intervals or reduce intensity in extreme heat
• • Focus on effort and heart rate, not pace during heat training

Perceived Exertion Adjustments

RPE increases in heat-calibrate expectations:

• • Zone 2 in heat feels like Zone 3 effort
• • Zone 4 in heat feels like Zone 5 effort
• • Trust heart rate monitor over perceived effort
• • Mental toughness component to heat training
• • Adaptation improves both physical and mental heat tolerance

Race Day Pacing

Use zones to pace hot weather races:

• • Start conservative: 5-10 bpm below normal race heart rate
• • Expect heart rate drift: HR increases as core temp rises
• • Slow pace to maintain target HR, don't chase pace
• • Cooling strategies: Ice, cold water, shade when possible
• • Hydration critical: Drink to thirst, electrolytes essential

Cool-Condition Baseline Testing

Santa Cruz's mild climate (60-75°F year-round) provides ideal conditions for baseline VO₂ max testing without heat interference. Establish true fitness before heat acclimation begins.

Controlled Heat Exposure

Train in cool mornings (Santa Cruz coast), then drive 30 minutes inland to San Jose/Los Gatos for afternoon heat training (85-95°F). Best of both worlds for periodized heat adaptation.

Recovery in Cool Climate

Sleep and recover in cool Santa Cruz climate while doing heat training during workouts. Better recovery than living in constant heat. Optimal for maintaining training volume during acclimation.

Plasma Volume Expansion (Most Important)

Heat training increases blood plasma volume by 10-20%:

• • More blood = better oxygen delivery to muscles
• • Increased stroke volume (more blood per heartbeat)
• • Lower heart rate at same workload
• • Improved thermoregulation (more blood for cooling)
• • Benefits persist 2-3 weeks after heat exposure ends
• • Provides performance boost even in cool conditions

Improved Sweating Response

Thermoregulation becomes more efficient:

• • Sweating starts earlier (lower core temperature threshold)
• • Higher sweat rate for better evaporative cooling
• • Sweat becomes more dilute (conserves sodium)
• • Better distribution of sweat across body surface
• • Reduced risk of heat exhaustion/stroke

Cardiovascular Adaptations

Heart and circulation become more efficient:

• • Lower resting and exercise heart rate
• • Increased cardiac output capacity
• • Better blood flow distribution (muscles + skin)
• • Reduced cardiovascular strain at given intensity
• • Improved heat tolerance during sustained exercise

Metabolic & Cellular Changes

Cellular-level adaptations:

• • Heat shock proteins protect cells from stress
• • Improved mitochondrial function
• • Better lactate clearance at submaximal intensities
• • Enhanced glycogen sparing (better fat oxidation)
• • Reduced oxidative stress during exercise

12-16 Weeks Before Race

Baseline VO₂ Max Testing

• • Test in cool conditions to establish true fitness
• • Record baseline VO₂ max, VT1, VT2, max HR
• • Get training zones for race preparation
• • Begin race-specific training block

3-4 Weeks Before Race

Begin Heat Acclimation

• • Start 2-week traditional heat protocol (if time allows)
• • Or begin post-workout sauna sessions (3-4 weeks)
• • Maintain training volume and intensity
• • Monitor body weight for dehydration

7-10 Days Before Race

Final Heat Exposure

• • Complete heat acclimation protocol
• • If traveling to race: arrive 5-7 days early for on-site acclimation
• • Begin taper (reduce volume, maintain intensity)
• • Practice race-day hydration and cooling strategies

Race Week

Final Preparation

• • Easy training only, maintain heat exposure (short sessions)
• • Pre-hydrate: Extra water + electrolytes 24-48 hours before
• • Plan cooling strategies: Ice, cold water, shade
• • Review heart rate zones and pacing plan

Race Day

Execution

• • Start conservative: 5-10 bpm below normal race HR
• • Accept heart rate drift as core temp rises
• • Slow pace to maintain target HR (don't chase pace)
• • Hydrate to thirst, electrolytes every 30-45 minutes
• • Use ice/cold water at aid stations

Summer Marathons

• • Grandma's Marathon (Duluth, MN): June, 60-75°F, humidity
• • San Francisco Marathon: July, 55-65°F but fog/wind challenges
• • Missoula Marathon (Montana): July, 65-80°F
• • Mayor's Marathon (Anchorage): June, 50-65°F (cool but long daylight)

Ironman Triathlons

• • Ironman Arizona: November, 70-85°F
• • Ironman Texas: April, 75-90°F, high humidity
• • Ironman Kona (World Championship): October, 85-95°F, extreme heat/humidity
• • Ironman Florida: November, 70-80°F, humid

Ultra Marathons

• • Western States 100: June, 90-110°F in canyons
• • Badwater 135: July, 120-130°F, Death Valley
• • Leadville 100: August, 40-80°F (altitude + heat)
• • Tahoe Rim Trail 100: July, 60-85°F, altitude

Pre-Race Hydration

24-48 hours before race:

• • Increase water intake: 0.5-1 oz per pound body weight daily
• • Add electrolytes: Sodium, potassium, magnesium
• • Monitor urine color: Pale yellow indicates good hydration
• • Avoid overhydration (hyponatremia risk)
• • Morning of race: 16-20 oz water 2-3 hours before start

During Race Hydration

Fluid and electrolyte needs during exercise:

• • Sweat rate: 1-2+ liters/hour in heat
• • Fluid intake: 16-32 oz/hour (drink to thirst)
• • Sodium: 500-1,000 mg/hour (via sports drink, salt tabs)
• • Carbohydrates: 60-90g/hour (gels, chews, drink)
• • Don't wait until thirsty-drink early and often

Signs of Dehydration

Warning signs during hot weather racing:

• • Heart rate 10+ bpm higher than expected
• • Reduced sweat rate (dry skin = danger)
• • Dizziness, confusion, disorientation
• • Muscle cramps (electrolyte depletion)
• • Dark urine color post-race
• • Weight loss 2%+ of body weight = performance impairment

How long does heat acclimation last?

Full acclimation takes 10-14 days and lasts 2-3 weeks after returning to cool conditions. For races, complete acclimation 1-7 days before event. Adaptations decay within 2-4 weeks without heat exposure.

Should I test before or after heat acclimation?

Both. Test before (baseline) and after (verify fitness maintained). Pre-acclimation test establishes zones for heat training. Post-acclimation test confirms you're ready for hot weather racing.

Can I do heat acclimation without access to hot weather?

Yes. Post-workout sauna or hot baths provide similar adaptations. Overdress during workouts (not recommended for safety). Or travel to hot location 7-14 days before race for acclimation.

Will heat training improve my cool-weather performance?

Yes. Heat acclimation increases plasma volume (more blood = better oxygen delivery), improves thermoregulation, and may enhance mitochondrial function. Many athletes see 2-3% performance gains in cool conditions after heat training.

What's the best time to do heat acclimation before a race?

Complete acclimation 1-7 days before race. Too early (3+ weeks) and adaptations decay. Too late (race week) and you're fatigued. Ideal: Finish acclimation 3-5 days before race, then taper.

Is heat training safe?

Yes, when done progressively. Start with shorter durations and lower intensities. Monitor core temperature if possible. Stop if you feel dizzy, nauseous, or stop sweating. Hydrate well before, during, and after heat sessions.

Can I maintain fitness during heat acclimation?

Yes. Use heart rate zones from baseline testing. Accept slower paces in heat while maintaining target heart rates. Quality workouts can be done in cool conditions (morning) while heat exposure happens separately (afternoon sauna).