Zone 2 Training for Hybrid Performance and HYROX-Relevant Outcomes
Zone 2 is best treated as a physiological domain rather than a fixed heart-rate (HR) number: it is the highest intensity that remains immediately below the first lactate or ventilatory threshold (often denoted LT1/VT1), where lactate and ventilation remain (relatively) stable and sustainable for long durations. [1]
Across modern practice, the term is used inconsistently because “Zone 2” can mean different things depending on whether an athlete/coach uses a 3-zone (threshold-domain) model or a 5–6-zone model. This is not a semantic problem; mislabeling changes the training stimulus and the expected adaptations. [2]
Biomarker expectations for Zone 2 align with classic endurance adaptations—improved mitochondrial content/oxidative capacity, improved capillarization and muscle oxygen extraction, improved fat oxidation at submaximal workloads, lower HR or lactate at a given external workload, and improved “durability” (reduced performance drop-off across prolonged work). [3]
However, key modern syntheses caution that these adaptations are not unique to Zone 2; nearby intensities can produce overlapping adaptations, and high-intensity work can be more time-efficient for some outcomes (especially VO₂max) depending on dose and athlete level. [4]
For HYROX-relevant performance, the best available peer-reviewed evidence remains early but informative. A simulated HYROX event (~86.5 min median) showed that running dominated total time (~51 min running vs ~33 min stations) and faster completion correlated strongly with higher VO₂max and greater endurance training volume, while strength proxy measures did not correlate in that small sample. [5]
Therefore, Zone 2’s most defensible HYROX pathway is indirect: building an aerobic base that improves running efficiency, enables more total training, and improves recovery between high-intensity stations—while recognizing bahwa race execution occurs largely at “hard/very hard” intensities and demands additional threshold/VO₂ and strength-endurance work. [6]
The primary research gaps are: (i) HYROX-specific longitudinal interventions isolating Zone 2 dose, (ii) validated hybrid performance models linking aerobic metrics to station-specific outcomes, (iii) standardized intensity prescription (threshold-based rather than %HRmax), and (iv) concurrent-training sequencing studies tailored to HYROX constraints. [7]
Defining Zone 2 and operationalizing it in the field
Physiological definition anchored to thresholds
A high-consensus definition from an expert panel is: Zone 2 should preferably be performed immediately below LT1/VT1 and can be implemented via continuous, variable, or interval-type sessions (with continuous long sessions common in practice). [1]
Why “below LT1/VT1” matters: lactate threshold constructs have multiple competing definitions, with ongoing debate about physiological meaning and test validity; therefore, “Zone 2” should reference a specific boundary concept (LT1/VT1) rather than “moderate” as a generic label. [8]
Even within threshold-based approaches, lactate and ventilatory thresholds can show meaningful disagreement, so they should not automatically be used interchangeably. [9]
Why Zone 2 numbers vary so much
Recent lab data in trained cyclists demonstrate that common Zone 2 markers (e.g., fixed %HRmax or fixed lactate values) have substantial intra- and interindividual variability (coefficients of variation ~6–29% across markers). VT1 and maximal fat oxidation (Fatmax) align better than fixed %HRmax or fixed lactate thresholds, supporting individualized prescriptions when precision matters. [10]
A key implication is that fixed HR rules are practical but may deliver incorrectly targeted metabolic strain for a non-trivial fraction of athletes. [11]
Mapping Zone 2 to HR, power, pace, and running power
The following table is a practical synthesis of how Zone 2 is commonly operationalized across modalities, while emphasizing that thresholds remain the academically preferred anchor.
| Metric family | Best-practice anchor (academic) | Common field proxy | Key pitfalls (why proxy can fail) |
| HR | HR at/just below VT1 or LT1 from graded test [9] | %HRmax ranges (e.g., ~73–82% HRmax used in Norwegian elite endurance “Zone 2” definitions) [12] | HR drift during prolonged work; HR–workload nonlinearity; hydration/heat effects; large individual error when using fixed percentages [13] |
| Cycling power (watts) | Power at/just below VT1/LT1 (lab) or MLSS-associated subthreshold marker [14] | %FTP “endurance” ranges (often used in practice) with FTP derived from TT tests [15] | FTP may not equal MLSS / maximal metabolic steady state; TT-derived corrections vary by athlete and protocol [15] |
| Running pace | Pace at/just below VT1/LT1; alternatively pace at first turn-point in lactate/ventilation [16] | “Conversational” pace (Talk Test), stable breathing, low RPE [17] | Terrain/heat/wind change pace at same metabolic cost; pace alone can overshoot Zone 2 on hills/heat; injury-risk constraints with high running volume [18] |
| Running power | Power at/near VT1/LT1 or MLSS, device-specific [19] | Stryd-based power targets show strong relationships with oxygen consumption in submax running; can be used to stabilize intensity across grade [20] | Devices can underestimate absolute power; cross-device comparability is limited; model choice affects “critical power/speed” estimates [21] |