“The 3 Energy Systems Explained: How to Train for Explosive Power, Endurance & Fat Loss (Zone 2, VO2 Max & FatMax Guide)”

The 3 Energy Systems — Clean Performance Breakdown

Read on to learn about the 3 energy systems, how to activate them, and examples.

1. Phosphagen System (ATP-PC / Creatine Phosphate)

“Explosive power system”

• Fuel: Creatine phosphate (PCr)
• Duration: ~0–10 seconds
• Intensity: Maximal (90–100%)
• ATP yield: Very low, but immediate
• Examples: Sprint start, jump, punch, heavy lift

Key Points

• Fastest system → instant energy
• No oxygen required
• Limited capacity → burns out quickly
• Replenished by aerobic system between efforts

Training focus:

• Short sprints
• Heavy lifts
• Plyometrics
• Long rest periods

Performance edge:

• Creatine increases phosphocreatine stores → improves repeat power output

2. Anaerobic Glycolytic System

“High-intensity repeat system”

• Fuel: Glycogen (carbohydrate)
• Duration: ~10–90 seconds (can extend to ~2 min)
• Intensity: High (75–90%)
• By-product: Lactate + H⁺ (burn)

Key Points

• Produces more power than aerobic, less than phosphagen
• Generates fatigue via acidity, not lactate itself
• Critical for repeated bursts

Training focus:

• Intervals (30–90 sec)
• Circuits
• Combat sport rounds
• Repeated sprint ability

Adaptation:

• Improved lactate tolerance
• Increased buffering capacity
• Better glycolytic efficiency

3. Aerobic (Oxidative) System

“Endurance + recovery system”

• Fuel:
• Fat (low/mod intensity)
• Carbohydrate (higher intensity)
• Protein (last resort)
• Duration: >90 seconds → hours
• Intensity: Low–moderate (<75–80%)
• ATP yield: Very high

Key Points

• Slow but massive energy output
• Requires oxygen
• Drives recovery between high-intensity efforts

Training focus:

• Zone 2 work
• Tempo efforts
• Long steady sessions

Fat Max & Heart Rate — Clarified Properly

Your explanation is good — here’s the clean, accurate coaching version:

Heart Rate Reserve (HRR) Formula

Take your resting heart rate (RHR).

Measure your Maximum Heart Rate (MHR).

Subtract your resting heart rate from your maximum heart rate giving your heart rate reserve (HRR). Multiply your HRR by the intensity you want to work at, e.g. 50% or 80%.

Where:

• HRR = Max HR – Resting HR

Example (Your numbers):

• Max HR = 180
• Resting HR = 60
• HRR = 120

Fat Max Estimates

Fat Max Level	Calculation	Target HR
60% (typical)	(120 × 0.6) + 60	132 bpm
75% (trained)	(120 × 0.75) + 60	150 bpm

 

Important Coaching Note

“Fat max” is not a fixed number — it shifts based on:

• Fitness level
• Mitochondrial density
• Diet (high fat vs high carb)
• Training history

Elite endurance athletes can oxidise fat at much higher intensities.

The Reality: Energy Systems Always Overlap

You nailed this — but here’s the sharper framing:

No system works in isolation

Situation	Dominant	Supporting
5-sec sprint	Phosphagen	Glycolytic
60-sec effort	Glycolytic	Aerobic
5-min round	Aerobic	Glycolytic bursts

 

Key Insight for Athletes

The aerobic system is the foundation of all repeat performance

• Replenishes ATP-PC stores
• Clears lactate
• Supports recovery between rounds

This is why even power athletes need aerobic conditioning.

Sport Application

Combat Sports (Boxing, MMA, Thai)

• Aerobic: sustain rounds, recovery between exchanges
• Glycolytic: flurries, grappling, clinch work
• Phosphagen: explosive strikes, takedowns

Best athletes = efficient in all 3 systems

Rugby / Intermittent Sports

• Constant switching:
• Sprint → jog → contact → repeat
• Requires:
• High aerobic base
• Strong glycolytic tolerance
• Explosive phosphagen power

Strength & Hypertrophy Section

Force Production Hierarchy

1. Isometric (highest force potential)
2. Eccentric (controlled lowering)
3. Concentric (lifting phase — weakest)

Hypertrophy & Metabolic Stress

Eccentric Training

• Highest muscle damage
• Strong hypertrophy stimulus
• Higher recovery cost

Concentric Emphasis

• Builds strength
• Less structural damage
• Useful for neural adaptations

Metabolic Stress

• Short rest periods
• High time under tension
• Oxygen limitation

Leads to:

• Growth factor release
• Hormonal signalling
• Cellular swelling

High-Level Coaching Takeaways

1. Aerobic system is underrated

• It determines how often you can repeat high-intensity work

2. Glycolytic system = “pain tolerance system”

• Train it to handle fatigue, not avoid it

3. Phosphagen = performance ceiling

• Determines peak power

“Power = Phosphagen
Sustain = Glycolytic
Repeat = Aerobic”

If you want, I can next:

• Turn this into a professional slide deck
• Build a boxing/MMA conditioning program using all 3 systems
• Or create a heart rate + energy system training template for clients

 

Great — this is where it gets really useful from a performance + coaching standpoint. I’ll split it into two parts:

Here’s the clean, research-based answer (no opinion, just what the literature shows):

What is the highest reasonable FatMax?

Evidence from research

1. Broad population range

• FatMax typically occurs at:
• ~45–65% of VO₂max in most people (Cycling Weekly)
• This roughly corresponds to:
• ~60–70% of max heart rate

2. Upper range in well-trained individuals

• Research shows FatMax can extend to:
• ~49–79% of VO₂max depending on training status (Springer)

This is key:

• Untrained / general population: ~45–60% VO₂max
• Recreationally trained: ~55–70% VO₂max
• Highly trained endurance athletes:
  can reach ~70–75%+ (occasionally approaching ~80%)

3. Physiological interpretation

• As intensity rises:
• Fat use ↑ → peaks (FatMax) → then declines as carbs dominate
• Around ~65% VO₂max, fat and carbs contribute ~50/50 (Wikipedia)

So what is the “reasonable highest”?

Evidence-based ceiling:

• ~75% VO₂max = realistic upper limit in elite / highly trained individuals
• ~80% VO₂max = extreme upper edge (rare, not typical)

Translating to Heart Rate

Approximate conversion:

VO₂max %	HRmax % (rough)
45–65%	~55–70% HRmax
65–75%	~70–80% HRmax
75–80%	~80–85% HRmax

So an estimate of 65% is NOT the upper limit
—it’s actually mid-range for trained individuals

Important nuance (often missed)

FatMax is not fixed — it shifts with:

• Aerobic fitness (biggest driver) (Taylor & Francis Online)
• Mitochondrial density
• Diet (fat-adapted vs high carb)
• Muscle oxidative capacity

• Typical population: ~45–65% VO₂max
• Well-trained: ~60–75% VO₂max
• Reasonable highest (research-supported):
  👉 ~75% VO₂max (occasionally up to ~80%)

Coaching Translation

“65% isn’t the ceiling — it’s where most people start.
The ceiling, if you’re well-trained, is closer to 75%+.”

PART 1 — Heart Rate Zones vs Substrate Use (Research-Aligned Model)

Core Principle

As intensity increases:

• Fat oxidation rises → peaks (FatMax) → declines
• Carbohydrate use rises exponentially

Simplified Substrate Curve

f(x)=\text{fat oxidation peaks at moderate intensity and declines as carbohydrate oxidation increases exponentially with intensity}

Practical HR-Based Breakdown

Zone	% HRmax	% VO₂max (approx)	Fuel Use	Key Notes
Zone 1	50–60%	~40–50%	🔥 High fat (~60–70%)	Very low output
Zone 2 (FatMax zone)	60–70%	~50–65%	🔥 Peak fat oxidation	Mitochondrial adaptations
Zone 3	70–80%	~65–75%	⚖️ Mixed (fat ↓, carbs ↑)	FatMax upper range
Zone 4	80–90%	~75–85%	⚡ Mostly carbs	Lactate rising
Zone 5	90–100%	~85–100%	⚡ Almost all carbs	Max effort

 

Key Research Takeaways

• FatMax typically sits ~60–75% VO₂max
• Above this:
• Fat contribution drops rapidly
• Carbohydrate dominates energy production

Even at FatMax:

• You are not burning only fat
• It’s simply the highest absolute rate of fat oxidation (g/min)

Important Distinction

Concept	Meaning
% Fat Burned	Proportion of fuel
FatMax	Absolute fat burned per minute

At higher intensities:

• % fat ↓
• BUT total energy ↑
  → fat burn may still be high just below FatMax

PART 2 — How to Increase FatMax (Evidence-Based)

Goal

Shift FatMax to the right (higher intensity)

1. Zone 2 Training (Primary Driver)

Mechanism:

• ↑ Mitochondrial density
• ↑ Fat oxidation enzymes (CPT-1, β-oxidation pathways)
• ↑ Capillary density

Protocol:

• 2–5 sessions/week
• 45–90 mins
• Intensity:
• ~60–70% HRmax
• Talk test: full sentences possible

Strongest evidence-backed method

2. Long Duration Training

• Extends reliance on fat metabolism
• Improves glycogen sparing

Especially effective when sessions exceed:

• 60–120 minutes

3. Fasted / Low Glycogen Training (Strategic Use)

Mechanism:

• Forces greater fat utilisation
• Upregulates fat oxidation pathways

Evidence:

• Mixed but supportive when used periodically

Use carefully:

• 1–2x/week max
• Low–moderate intensity only

4. 🍽️ Nutritional Influence

Higher fat oxidation associated with:

• Lower chronic carbohydrate availability
• Higher fat intake (to a degree)

BUT:

• High-carb diets still support strong FatMax if training is appropriate

Training > diet for shifting FatMax

5. Aerobic Fitness Level (Biggest Factor)

Research consistently shows:

VO₂max ↑ → FatMax shifts to higher intensities

6. Interval Training (Supportive, Not Primary)

• Improves mitochondrial function
• Enhances metabolic flexibility

Works best combined with Zone 2

Putting It Together (Coaching Model)

Beginner

• FatMax ~50–60% VO₂max
  Focus: build aerobic base

Intermediate

• FatMax ~60–70%
  Add longer sessions + some intervals

Advanced

• FatMax ~70–75%+
  High efficiency + metabolic flexibility

High-Level Summary

What determines FatMax most?

1. Mitochondrial density
2. Aerobic conditioning
3. Metabolic flexibility

Practical coaching line:

“If you want to burn fat at higher intensities,
you don’t train harder —
you train longer and more efficiently first.”

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