Fat Burning Zone Testing in Santa Cruz

Understanding how your body burns fat during exercise:

• Substrate Utilization Continuum:
  • • At rest: 60 to 70% energy from fat, 30 to 40% from carbohydrates
  • • Low intensity (40 to 60% VO₂ max): 50 to 60% fat, 40 to 50% carbs
  • • FatMax intensity (60 to 70% VO₂ max): 55 to 65% fat, 35 to 45% carbs (absolute fat burning peaks here)
  • • Moderate intensity (70 to 80% VO₂ max): 40 to 50% fat, 50 to 60% carbs (absolute fat burning declining)
  • • High intensity (85%+ VO₂ max): 20 to 30% fat, 70 to 80% carbs (fat burning minimal)
• Why Fat Oxidation Peaks Then Declines:
  • • Low Intensity: Fat oxidation high as % but total calories burned low, so grams fat/min moderate
  • • FatMax Intensity: Optimal combination of moderate % fat + higher total calories = maximum grams fat/min
  • • High Intensity: Total calories very high but fat % crashes, carb metabolism dominates, fat grams/min decline
  • • Mechanism: High intensity inhibits fat breakdown (lipolysis) and fat transport into mitochondria
• Respiratory Exchange Ratio (RER):
  • • RER = CO₂ produced / O₂ consumed
  • • RER 0.70 = 100% fat oxidation (never reached during exercise)
  • • RER 0.85 = ~50% fat, 50% carb (typical at FatMax)
  • • RER 1.00 = 100% carbohydrate (at and above lactate threshold)
  • • We measure RER breath-by-breath to determine fat vs. carb metabolism

Our VO₂ max testing reveals both ABSOLUTE fat oxidation and the intensity where it peaks:

• Testing Protocol:
  • • Graded exercise test with intensity increasing every minute
  • • Breath-by-breath measurement of O₂ consumption and CO₂ production
  • • Calculate RER to determine % fat vs. carb at each intensity
  • • Test continues through all intensities to true VO₂ max
• Fat Oxidation Calculation:
  • • Use RER and VO₂ to calculate grams of fat oxidized per minute
  • • Formula: Fat oxidation = 1.695 × VO₂ - 1.701 × VCO₂ (Frayn equation)
  • • Plot fat oxidation across all intensities
  • • Identify peak (FatMax)
• Your Results Include:
  • • FatMax intensity (% VO₂ max and heart rate)
  • • Maximum fat oxidation rate (grams per minute)
  • • Fat oxidation curve across all intensities
  • • Zone 2 range (optimal for fat adaptation training)
  • • Training recommendations for improving fat metabolism

Why fitness trackers and cardio machines get it wrong:

• Generic "Fat Burn Zone" (Fitness Trackers):
  • • Based on age-predicted max HR formula (220-age)
  • • "Fat burn" typically 60 to 70% of predicted max HR
  • • No actual measurement of YOUR fat oxidation
  • • Can be off by 20+ bpm from your true FatMax
• Example of Inaccuracy:
  • • 40-year-old predicted max HR: 180 bpm
  • • Generic "fat burn zone": 108 to 126 bpm (60 to 70%)
  • • Actual max HR (from testing): 195 bpm
  • • Actual FatMax (from testing): 140 bpm (72% true max)
  • • Result: Generic zone is WAY too easy, missing actual FatMax by 15+ bpm
• Individual Variation:
  • • Two people same age, same max HR can have FatMax 20 bpm apart
  • • Training history, genetics, diet all influence FatMax location
  • • Only way to know: measure it

How to enhance your body's ability to burn fat at higher intensities:

• Zone 2 Training (Primary Method):
  • • Train at intensity just below FatMax (typically Zone 2)
  • • High volume: 4 to 6+ hours per week
  • • Adaptations: Increased mitochondrial enzymes for fat metabolism, more fat-burning capacity
  • • Timeline: Measurable improvement in 8 to 12 weeks
  • • Result: FatMax shifts to HIGHER intensity, peak fat oxidation rate increases
• Low-Carb Training Sessions:
  • • Occasionally train in fasted state or after low-carb meal
  • • Forces body to rely more on fat metabolism
  • • Do NOT do this for all training-only 1 to 2 sessions per week
  • • Keep intensity low (Zone 1 to 2)
  • • Controversial approach-not necessary for fat adaptation but may accelerate
• Dietary Considerations:
  • • Adequate healthy fats in diet (30 to 40% calories)
  • • Not necessarily low-carb diet-body needs carbs for high-intensity training
  • • Nutrient timing: Easy sessions fasted or low-carb, hard sessions fully fueled
• Expected Improvements:
  • • Beginner: FatMax increases from 50% to 60% VO₂ max in 12 weeks
  • • Trained: Peak fat oxidation increases from 0.5 to 0.8 g/min
  • • Performance benefit: Can sustain higher pace/power before depleting glycogen

How to use fat oxidation data for body composition goals:

• The Calorie Deficit Truth:
  • • Weight loss requires calorie deficit, regardless of substrate (fat vs. carb) burned during exercise
  • • HOWEVER, training at FatMax has specific benefits for weight loss
  • • More sustainable, higher total calorie burn, better adherence
• Benefits of FatMax Training for Weight Loss:
  • • Sustainability: Can exercise longer at FatMax intensity (60 to 90 min) vs. high intensity (20 to 30 min)
  • • Total Calories: 60 min at FatMax burns MORE total fat than 20 min high intensity
  • • Recovery: Low-intensity work allows daily exercise without fatigue
  • • Adherence: Comfortable effort = more likely to stick with program long-term
  • • Appetite Control: Moderate intensity less likely to trigger excessive hunger vs. high intensity
• Sample Fat Loss Exercise Plan:
  • • 5 to 6 days per week
  • • 45 to 90 minutes per session
  • • Heart rate at YOUR FatMax (identified through testing)
  • • Activities: Walking, jogging, cycling, elliptical, rowing
  • • Combined with RMR-based nutrition plan for optimal deficit
• Myth Busting:
  • • Myth: "High intensity burns more fat than low intensity"
  • • Truth: High intensity burns more total calories but LESS fat per minute. For fat loss, total calorie deficit over weeks matters most
  • • Best Approach: Mostly FatMax training (high volume) + occasional HIIT (metabolic boost) + strength training (preserve muscle)

Why ultra-runners, Ironman athletes, and cyclists care about fat oxidation:

• Glycogen Limitation:
  • • Body stores ~2000 calories as glycogen (muscle and liver)
  • • Running burns ~100 calories per mile = glycogen depleted after 20 miles
  • • Cycling burns ~40 calories per mile = glycogen depleted after 50 miles
  • • Marathon: 26 miles. Ultra: 50 to 100 miles. Ironman: 140 miles. ALL exceed glycogen stores
• Fat as Abundant Fuel:
  • • Even lean athlete stores 50,000+ calories as body fat
  • • Virtually unlimited energy if you can access it
  • • The athlete who oxidizes fat at higher intensities wins ultra-endurance events
• Performance Applications:
  • • Marathon: Pace at 75 to 85% VO₂ max. If FatMax is 70%, hitting "the wall" likely. If FatMax is 75%, can sustain pace on less carb intake
  • • Ironman: Bike and run at 60 to 70% VO₂ max. High FatMax critical for maintaining pace 6 to 12 hours
  • • 100-Mile Ultras: Pace at 50 to 65% VO₂ max. Must operate primarily on fat. Elite ultrarunners have exceptional fat oxidation
• Fueling Strategy:
  • • Higher fat oxidation = need fewer carb gels/drinks = less GI distress
  • • Can consume 30 to 60 g carbs/hour instead of 60 to 90 g/hour
  • • Simpler nutrition strategy, lower cost, less nausea risk

Fat oxidation capacity as a marker of metabolic health:

• What is Metabolic Flexibility?
  • • Ability to efficiently switch between burning carbs and fat based on availability and demand
  • • Healthy metabolism adapts fuel source seamlessly
  • • Metabolic inflexibility (insulin resistance, metabolic syndrome) = impaired fat oxidation
• Implications:
  • • Low fat oxidation capacity associated with obesity, Type 2 diabetes, cardiovascular disease
  • • Improving fat oxidation (through exercise) improves metabolic health markers
  • • Exercise at FatMax intensity may be therapeutic for metabolic syndrome
• Research Support:
  • • Studies show training at FatMax improves insulin sensitivity
  • • Enhances blood lipid profiles (triglycerides, HDL cholesterol)
  • • Reduces inflammation markers

Misconceptions about fat metabolism during exercise:

• Myth: "Lower intensity always burns more fat."
  • • Truth: Lower intensity burns higher PERCENTAGE fat, but lower TOTAL fat per minute
  • • Walking: 80% fat, but only 0.1 g fat/min
  • • FatMax intensity: 55% fat, but 0.8 g fat/min
  • • FatMax wins for fat burning per unit time
• Myth: "You don't burn fat until 20 minutes of exercise."
  • • Truth: Fat burning begins immediately when you start exercising
  • • Ratio shifts slightly over time (more fat as glycogen depletes) but fat oxidation is always happening
  • • This myth likely comes from misunderstanding glycogen vs. blood glucose utilization
• Myth: "Fasted cardio always burns more fat."
  • • Truth: Fasted training burns more fat DURING the session, but 24-hour fat balance is what matters for weight loss
  • • Studies show no difference in fat loss between fasted vs. fed cardio when calories matched
  • • However, fasted training may enhance fat-burning adaptations over time (trains the pathway)
• Myth: "High-intensity interval training burns more fat."
  • • Truth: HIIT burns mostly carbs during exercise, with EPOC (excess post-exercise oxygen consumption) providing modest extra calorie burn
  • • Total 24-hour fat oxidation similar between FatMax training and HIIT when calories matched
  • • Both effective for fat loss via calorie deficit; FatMax training more sustainable for high volume

How to track fat metabolism improvements:

• Initial Test: Establish baseline FatMax intensity and peak fat oxidation rate
• After 12 to 16 Weeks Training: Retest to assess adaptation
• Expected Changes:
  • • FatMax shifts to higher % VO₂ max (e.g., from 55% to 65%)
  • • Peak fat oxidation rate increases (e.g., from 0.4 to 0.7 g/min)
  • • Fat oxidation remains higher across all intensities
• Performance Translation: You can now burn fat at faster pace/higher power, sparing glycogen for surges

VO₂ Max Test with Fat Oxidation Analysis: $250

What's Included:

• • Complete VO₂ max assessment
• • FatMax determination (intensity of peak fat oxidation)
• • Maximum fat oxidation rate (grams per minute)
• • Fat oxidation curve across all intensities
• • Training zones optimized for fat adaptation
• • Nutrition and training recommendations
• • Same-day results with detailed interpretation

Fit Evaluations
311 Soquel Ave
Santa Cruz, CA 95062

Behind Hindquarter restaurant (second entrance off Dakota St.)

Phone: 831-400-9227
Email: info@fitevals.com