What training zones correlate best with moderate and high-intensity aerobic activities?

From the Guidelines

Moderate aerobic activities typically correlate with training zones 2-3, while high-intensity aerobic activities align with zones 4-5. Zone 2 (60-70% of maximum heart rate) represents light to moderate intensity where you can maintain conversation and is ideal for building aerobic base and fat burning, as supported by the 2024 ESC guidelines for the management of elevated blood pressure and hypertension 1. Zone 3 (70-80%) is moderate intensity where conversation becomes more difficult but still possible, improving aerobic capacity and endurance. For high-intensity work, Zone 4 (80-90%) represents the threshold where lactic acid begins accumulating and breathing becomes labored, while Zone 5 (90-100%) is maximum effort that can only be sustained for short periods.

Some key points to consider when implementing these zones include:

• Calculating your maximum heart rate (roughly 220 minus your age) and then determining the corresponding heart rate ranges, as suggested in the evidence summaries and recommendations from the international evidence-based guideline for the assessment and management of polycystic ovary syndrome 1.
• Understanding that these zones target different energy systems - lower zones primarily use fat as fuel and build mitochondrial density, while higher zones improve VO2 max, lactate threshold, and anaerobic capacity.
• Recognizing the importance of training across multiple zones to provide complementary benefits for overall cardiovascular fitness, as emphasized in the core components of cardiac rehabilitation programs: 2024 update 1.
• Considering the recommendations for physical activity and exercise from various guidelines, such as the 2025 standards of care in diabetes, which counsel adults with type 1 diabetes and type 2 diabetes to engage in 150 min or more of moderate- to vigorous-intensity aerobic activity per week 1.

Overall, training zones 2-3 are suitable for moderate aerobic activities, while zones 4-5 are more appropriate for high-intensity aerobic activities, as supported by the most recent and highest quality studies, including those from 2024 and 2025 1.

From the Research

Training Zones for Moderate and High-Intensity Aerobic Activities

The correlation between training zones and moderate and high-intensity aerobic activities can be understood by examining the following points:

• Moderate-intensity aerobic activities are typically associated with zones where the heart rate is at 50-70% of the maximum heart rate [ 2, 3 ]
• High-intensity aerobic activities are associated with zones where the heart rate is at 70-90% of the maximum heart rate [ 4, 3 ]
• For endurance sports, heart rate variability-derived thresholds (HRVTs) can be used to determine the intensity zones, with HRVTlow corresponding to the lower threshold and HRVThigh corresponding to the higher threshold 5
• The American College of Sports Medicine (ACSM) recommends the following zones for aerobic exercise:
  • Zone 1: 50-60% of maximum heart rate (low-intensity)
  • Zone 2: 60-70% of maximum heart rate (moderate-intensity)
  • Zone 3: 70-80% of maximum heart rate (high-intensity)
  • Zone 4: 80-90% of maximum heart rate (very high-intensity)
  • Zone 5: 90-100% of maximum heart rate (extremely high-intensity) 3, 6

Key Findings

• Higher intensities of exercise are more effective for improving VO2max than lower intensities of exercise in healthy, young adults 3
• Chronic exercise durations >9% of total exercise time in the >90% maximum HR zone can lead to decreased variation in salivary cortisol concentration after exercise 6
• The ideal duration for training time above 90% maximum HR is 4% to 9% of total training time to maximize fitness and minimize symptoms related to overreaching 6