Summary of "The Real Science of Zone 2 Training (Not the Hype)"

Summary of Key Wellness, Self-Care, and Training Strategies from The Real Science of Zone 2 Training (Not the Hype)

Understanding Zone 2 Training

Zone 2 training is defined by the lactate curve as the intensity just before the first lactate breakpoint (~0.5 mmol/L), where the aerobic system predominates. It is characterized by:

Ability to talk comfortably during exercise (Talking Test).
Rating of Perceived Exertion (RPE) around 3-4 out of 10.
Heart rate roughly 70-80% of max (though less reliable for intermittent sports).
Muscle oxygen saturation can also indicate Zone 2 intensity.

Key Physiological Mechanisms

AMPK (AMP-activated kinase) is a key regulator of mitochondrial biogenesis, sensing cellular energy levels via the ADP:ATP ratio.
Long-duration, low-load (endurance) exercise activates AMPK, increasing PGC1-alpha gene expression, which promotes mitochondrial growth and aerobic capacity.
However, recent research suggests:
- Zone 2 training does not consistently activate AMPK.
- Higher intensity training often produces greater AMPK activation and mitochondrial adaptations.

Training Volume vs. Intensity

A meta-analysis shows mitochondrial density correlates with training load (a combination of intensity, duration, and frequency), not just low-intensity volume.
High-intensity interval training (HIIT) and sprint interval training (SIT) can also increase mitochondrial content effectively.
Endurance athletes typically perform a lot of Zone 2 work because it allows:
- High training volume with low physiological strain.
- Faster recovery and sustainable aerobic adaptations.

Specific Adaptations of Zone 2

Zone 2 training promotes:

Greater fat oxidation.
Glycogen sparing.
Reduced reliance on glycolytic (anaerobic) metabolism.

Chronic exposure to high lactate (from glycolytic work) may impair mitochondrial function, suggesting a potential trade-off in sports like CrossFit.

Observations in Functional and High-Intensity Sports (CrossFit, Hyrox)

Many CrossFit athletes lack a clear Zone 2 lactate curve due to predominantly high-intensity training.
Elite CrossFit athletes can sustain power well above their lactate threshold due to superior glycolytic and buffering capacity.
Hyrox athletes (a hybrid endurance-functional sport) benefit from a balance of low and high-intensity training.

Practical Training Recommendations

For Recreational CrossFitters (4x/week)

Focus on metcons, strength, and skill work.
Minimal low-intensity (Zone 2) work needed.

For RX-level CrossFit Athletes

Incorporate 1-2 low-intensity aerobic sessions per week (e.g., 25-minute EOMs with light movements).
Majority of training remains high intensity and strength-focused.

For Elite CrossFit Athletes

Add 2-3 sessions of low-intensity aerobic work weekly to increase training volume and aid recovery.

For Hyrox Athletes

Average athletes: prioritize training above lactate threshold for benefits.
RX athletes: balance 50/50 low and high-intensity training.
Elite athletes: perform large volumes (~70-80%) of low-intensity aerobic work for endurance base.

Summary Insights

Zone 2 training is not the only path to mitochondrial adaptations; higher intensities can be equally or more effective.
Zone 2 remains valuable for endurance athletes due to low physiological strain and recovery benefits.
Functional fitness and glycolytic sports benefit from a hybrid approach, emphasizing high-intensity work but incorporating some low-intensity aerobic training for volume and recovery.
Monitoring lactate, perceived exertion, and muscle oxygenation can help individualize training zones.

Presenters and Sources

Gomar – Senior scientist at ETH Zurich, exercise physiology expert, and presenter of the video.
Research and papers referenced include:
- Christie Stoshuk (narrative review on AMPK and mitochondrial biogenesis).
- Cesar Granada and David Bishop group (2018 meta-analysis on mitochondrial adaptations).
- Sandbach Heal (Norwegian endurance coaches’ training characteristics).
- Inigo San Milan (research on lactate effects on mitochondria).
Athlete examples: Lucas Eslinger (CrossFit athlete), Mayhem athletes, and elite CrossFit Games competitors.

This summary captures the scientific insights and practical training advice related to Zone 2 training and its role in different sports contexts.