What Is “Zone 2 Training”?: Experts’ Viewpoint on Definition, Training Methods, and Expected Adaptations

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Study Details

Authors
Sebastian Sitko, Xabier Artetxe, Martin Bonnevie-Svendsen, Miguel Ángel Galán-Rioja, Gabriele Gallo, Frédéric Grappe, Peter Leo, Manuel Mateo & others
Published
2025
View the study
Citation
Sitko, S., Artetxe, X., Bonnevie-Svendsen, M., Galán-Rioja, M. Á., Gallo, G., Grappe, F., ... & Viribay, A. (2025). What is “Zone 2 Training”?: Experts’ Viewpoint on Definition, Training Methods, and Expected Adaptations. International Journal of Sports Physiology and Performance. Advance online publication. https://doi.org/10.1123/ijspp.2024-0303

“Zone 2 training” has become a popular topic among endurance athletes and coaches, often praised for its ability to induce a wide range of aerobic adaptations. However, definitions of Zone 2 vary, leading to confusion around how it should be implemented and what benefits to expect. This expert commentary, developed by 14 applied sport scientists and professional coaches, aims to build consensus around how Zone 2 training is best defined, how it should be applied in practice, and what types of physiological changes it is likely to stimulate.

Zone 2 Is Just Below the First Lactate or Ventilatory Threshold

  • Experts agreed that Zone 2 corresponds to intensities just below LT1 or VT1, where physiological responses remain stable or only slightly elevated.
  • Common markers include:
    • Heart rate: 70–80% of HRmax, or ~80–90% of LT1 HR
    • Blood lactate: ~1–2 mmol/L
    • RPE: ~10 (on Borg 6–20 scale)
    • Power output: ~75–80% of critical power
  • Monitoring both internal (HR, RPE) and external (power/speed) load is key to preserving intended intensity, especially as fatigue accumulates.

Three Common Zone 2 Training Methods

  • Continuous Sessions
    • Long steady rides (ideally >2 hours) performed entirely at Zone 2 intensity.
    • Coaches should adjust intensity based on HR and RPE, especially if fatigue or cardiac drift appears.
  • Variable Continuous Sessions
    • Interspersing Zone 2 work with short bouts of Zone 1 (e.g., 5:1 ratio) can reduce monotony while maintaining training stimulus.
  • Interval Sessions
    • Zone 2 can be integrated between high-intensity intervals (e.g., during active recovery) or at the end of sessions once high-intensity work is no longer possible.
    • These sessions are usually shorter (≤2 hours) but still offer valuable time at target intensity.

Expected Adaptations from Zone 2 Training

  • Experts anticipated a variety of central and peripheral adaptations, including:
    • Increased muscle capillarization and mitochondrial enzyme activity
    • Improved metabolic efficiency and fat oxidation capacity
    • Modest increases in critical power and VO2max
  • A key adaptive shift is the compression of LT1/VT1 toward LT2/VT2, indicating improved endurance capacity.
  • Cognitive resilience was also noted as an adaptation, given the mental effort required for long, low-intensity sessions.

Adaptations Occur on a Continuum, Not Within Rigid Zones

  • The panel emphasized that adaptations are not exclusive to Zone 2 and likely occur across a continuum of intensities.
  • Therefore, training slightly above or below this zone may still produce similar benefits, especially when guided by internal load markers.

Practical Applications for Coaches and Endurance Athletes

  • Zone 2 training should be anchored to physiological thresholds, not arbitrary percentages of max heart rate or pace.
  • To get the most out of Zone 2 training:
    • Use HR and RPE to monitor internal load
    • Be flexible with intensity if cardiac drift or fatigue appears
    • Embrace session variation (e.g., steady, variable, intervals) to match training goals and reduce mental fatigue
  • While evidence is still emerging, long continuous sessions just below LT1/VT1 appear to be a cornerstone of aerobic development in endurance sports.