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(2) The Specificity Problem: Why Polarized Training May Not Be Built for Ultramarathons

/8 min read

The Zone 2 Paradox

Polarized training prescribes most training time below the first ventilatory threshold (Zone 1), a meaningful fraction above the second threshold (Zone 3), and minimal time in the "grey zone" between them (Zone 2). The logic is coherent: avoid the metabolically costly middle that is too hard to recover from quickly but not intense enough to drive the adaptations of true high-intensity work. The specificity principle — one of the most robustly replicated ideas in exercise science — says something more demanding: the adaptations that transfer to performance are those trained under conditions resembling the event. For ultramarathon running, those two principles may not point in the same direction.

How Hard Ultras Actually Are

The "ultras are a Zone 2 race" framing is not well supported by field data. A 2018 study in the Journal of Sports Sciences measured time-in-zone during a 65 km mountain ultra and found roughly 86% of race time spent below VT1 — Zone 1 by any standard model. Fornasiero et al. (2017, Frontiers in Physiology) measured mean intensity at the Tor des Géants 330 km race at 57.3% VO₂peak, and one case study at Western States 100 recorded approximately 51% VO₂max during a representative running segment. The pattern is consistent: intensity decreases sharply with duration, from around 60–70% VO₂max in 6-hour events to 40–50% in 24-hour events. For elite athletes with a high aerobic threshold, much of that race time falls in Zone 1. The Zone 2 specificity argument is real for recreational athletes whose aerobic threshold is lower, but it does not apply universally.

The Evidence Gap

The more consequential problem is what the research base does not contain. Oliveira et al. (2024, Sports Medicine) found polarized training superior for VO₂peak only in interventions shorter than 12 weeks and in highly trained athletes; time-trial performance differences were non-significant. Rosenblat et al. (2019, JSCR) identified four qualifying RCTs — all in cyclists, runners, and triathletes — with performance outcomes measured over 20–30 minute maximal efforts. The foundational Stöggl and Sperlich 2014 trial ran for nine weeks in athletes competing up to marathon distance. No polarized training RCT has recruited an ultra-distance population, and no study has measured performance over efforts longer than approximately 40 minutes. The gap between the studied context and a 100-mile mountain race is roughly 40-fold in event duration — not incremental extrapolation but a categorical discontinuity.

Durability Is the Binding Constraint

The concept that most clearly exposes this discontinuity is durability, defined by Maunder et al. (2021, Sports Medicine) as the resilience to deterioration of physiological parameters during prolonged exercise. Matomäki et al. (2023, Frontiers in Physiology) ran a 10-week trial in non-ultra runners comparing low-intensity and high-intensity training and found both improved durability equivalently, while VO₂max improved only with high-intensity work. Polarized training's primary adaptation — a raised aerobic ceiling — does not produce superior durability outcomes compared to sustained low-to-moderate intensity volume. For an event in which physiological deterioration begins within the first few hours and accumulates across the remainder, this matters more than the ceiling.

The Neuromuscular Mismatch

Metabolic zone distributions miss a second problem entirely. Millet et al. (2011, PLOS ONE) assessed 22 runners after a 166 km mountain ultra and found knee extensor maximal voluntary contraction reduced by 35%, plantar flexor MVC reduced by 39%, and creatine kinase elevated 127-fold. Recovery to baseline required 9 to 16 days. Their data indicate that mountain-specific downhill volume is necessary for adequate neuromuscular adaptation, and flat-terrain training does not provide the same stimulus. The sports that produced the evidence base for polarized training — cycling and rowing — involve no downhill eccentric loading. A training model validated on ergometers does not automatically transfer to terrain that damages the legs through a fundamentally different mechanism.

Implication for Training

The most credible counterargument is that VO₂max still matters: Sabater-Pastor et al. (2023, IJSPP) found that velocity at VO₂max (vVO₂max) explained up to 65% of variance in a 166 km trail race. An aerobic ceiling is real. But prediction in a cross-sectional study does not imply that VO₂max-focused training is the optimal stimulus for ultra adaptation. Published data from elite ultra athletes points toward pyramidal distributions: Sperlich, Matzka and Holmberg (2023) found elite endurance training predominantly pyramidal across 175 reviewed distributions, and Jornet's own 2022 published training data shows 16% Zone 2 and 7% Zone 3. For athletes preparing for long mountain ultras, sustained moderate-intensity long efforts that build durability, combined with downhill loading for neuromuscular resilience, have more mechanistic logic and more athlete data behind them than classically polarized training — even as the definitive RCT in an ultra population remains unwritten.

Sources

Race Physiology and Intensity Profiles

  1. Vernillo G, et al., "Physiological intensity profile of a 65‑km mountain ultra‑marathon" Journal of Sports Sciences, 2018 https://doi.org/10.1080/02640414.2017.1374707

  2. Fornasiero A, et al., "The Energetics during the World's Most Challenging Mountain Ultra-Marathon (Tor des Géants)" Frontiers in Physiology, 2017 https://doi.org/10.3389/fphys.2017.01003

  3. Stuempfle KJ, Hoffman MD, "Indirect Calorimetry During Ultradistance Running: A Case Report (Western States 100)" Journal of Sports Science and Medicine, 2006 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3827564/

  4. Garbisu-Hualde A, Santos-Concejero J, "What are the Limiting Factors During an Ultra-Marathon? A Systematic Review" Journal of Human Kinetics, 2020 https://doi.org/10.2478/hukin-2019-0102

  5. Wolfarth B, et al., "Influence of a 100-mile ultramarathon on heart rate and heart rate variability" BMJ Open Sport and Exercise Medicine, 2020 https://doi.org/10.1136/bmjsem-2020-001005

  6. Esteve-Lanao J, et al., "How Do Humans Control Physiological Strain during Strenuous Endurance Exercise?" PLOS ONE, 2008 https://doi.org/10.1371/journal.pone.0002943

Polarized Training Research

  1. Stöggl T, Sperlich B, "Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training" Frontiers in Physiology, 2014 https://doi.org/10.3389/fphys.2014.00033

  2. Oliveira PS, Boppre G, Fonseca H, "Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance" Sports Medicine, 2024 https://doi.org/10.1007/s40279-024-02034-z

  3. Rosenblat MA, Perrotta AS, Vicenzino B, "Polarized vs. Threshold Training Intensity Distribution on Endurance Sport Performance: A Systematic Review" Journal of Strength and Conditioning Research, 2019 https://doi.org/10.1519/JSC.0000000000002618

  4. Filipas L, et al., "Effects of plyometric training on different 8-week training intensity distributions in well-trained endurance runners" Scandinavian Journal of Medicine and Science in Sports, 2022 https://doi.org/10.1111/sms.14257

  5. Seiler KS, Kjerland GØ, "Quantifying training intensity distribution in elite endurance athletes" Scandinavian Journal of Medicine and Science in Sports, 2006 https://doi.org/10.1111/j.1600-0838.2004.00418.x

  6. Bauer N, et al., "Effects of Different Training Intensity Distributions in Breast and Prostate Cancer Survivors" European Journal of Sport Science, 2025 https://doi.org/10.1002/ejsc.12287

  7. Muñoz I, et al., "Eleven‑Week Preparation Involving Polarized Intensity Distribution Is Not Superior to Pyramidal Distribution in National Elite Rowers" Frontiers in Physiology, 2017 https://doi.org/10.3389/fphys.2017.00515

Durability and Metabolic Adaptation

  1. Maunder E, et al., "The Importance of 'Durability' in the Physiological Profiling of Endurance Athletes" Sports Medicine, 2021 https://doi.org/10.1007/s40279-021-01459-0

  2. Matomäki P, et al., "Durability is improved by both low and high intensity endurance training" Frontiers in Physiology, 2023 https://doi.org/10.3389/fphys.2023.1128111

  3. Hunter B, Muniz-Pumares D, "Durability of Parameters Associated With Endurance Running Performance in Marathoners" European Journal of Sport Science, 2025 https://doi.org/10.1002/ejsc.70073

  4. Maunder E, et al., "Peak fat oxidation is positively associated with vastus lateralis CD36 content, fed-state exercise fat oxidation, and endurance performance" European Journal of Applied Physiology, 2021 https://doi.org/10.1007/s00421-021-04820-3

  5. Meixner B, et al., "Zone 2 Intensity: A Critical Comparison of Individual Variability" Translational Sports Medicine, 2025 https://doi.org/10.1155/tsm2/2008291

  6. Maunder E, et al., "Prolonged exercise reduces power output at the moderate-to-heavy intensity transition" European Journal of Applied Physiology, 2022 https://doi.org/10.1007/s00421-022-05036-9

Neuromuscular Demands of Mountain Running

  1. Millet GY, et al., "Neuromuscular Consequences of an Extreme Mountain Ultra-Marathon" PLOS ONE, 2011 https://doi.org/10.1371/journal.pone.0017059

  2. Degache F, et al., "Alterations of Neuromuscular Function after the World's Most Challenging Mountain Ultra-Marathon (Tor des Géants)" PLOS ONE, 2013 https://doi.org/10.1371/journal.pone.0065596

  3. Lloria-Varella J, et al., "Assessing Physiological Durability in Trail Runners: A Terrain-Specific Protocol" International Journal of Sports Physiology and Performance, 2025 https://doi.org/10.1123/ijspp.2025-0307

  4. Partyka M, Waśkiewicz Z, "Musculoskeletal Consequences of Ultra-Marathon Races: A Systematic Narrative Review" Frontiers in Physiology, 2021 https://doi.org/10.3389/fphys.2021.738665

Training Intensity Distribution and Elite Athletes

  1. Sperlich B, Matzka M, Holmberg HC, "The proportional distribution of training by elite endurance athletes at different exercise intensity" Frontiers in Sport and Active Living, 2023 https://doi.org/10.3389/fspor.2023.1258585

  2. Rivera-Kofler T, et al., "Anthropometric Characteristics, Training Intensity Distribution and Physiological Profile of an Elite Trail Runner: A Longitudinal Case Study" International Journal of Morphology, 2024 https://doi.org/10.4067/s0717-95022024000200416

  3. Roche D, "Eight Takeaways From Kilian Jornet's 2022 Training Data" Trail Runner Magazine, 2022 https://www.trailrunnermag.com/training/trail-tips-training/kilian-jornet-training-data/

  4. COROS, "Inside Kilian Jornet's Training Data" COROS, 2025 https://coros.com/stories/more-than-splits/c/kilian-jornet-training

  5. Jaén-Carrillo D, Margarit-Boscà A, "Reverse periodization in ultratrail: Road to the 2023 World Championships" Ciencias del Deporte, 2024 https://doi.org/10.36950/2024.4ciss039

Performance Determinants

  1. Sabater-Pastor F, et al., "VO₂max and Velocity at VO₂max Play a Role in Ultradistance Trail-Running Performance" International Journal of Sports Physiology and Performance, 2023 https://doi.org/10.1123/ijspp.2022-0275

  2. Rapp E, et al., "The effect of XC-running race on determinants of performance: VO₂ at lactate threshold, fat utilization, and running economy" Frontiers in Physiology, 2025 https://doi.org/10.3389/fphys.2025.1647810

  3. Casado A, et al., "Does Lactate-Guided Threshold Interval Training Represent the Next Step in the Evolution of Distance Running Training?" International Journal of Environmental Research and Public Health, 2023 https://doi.org/10.3390/ijerph20053782

Coaching and Applied

  1. Roche D, "The Exciting Complexity of Threshold Training for Trail Running" Trail Runner Magazine, 2023 https://www.trailrunnermag.com/training/trail-tips-training/the-exciting-complexity-of-threshold-training-for-trail-running/

  2. Hutchinson A, "The Case For (and Against) Polarized Training" Outside Online, 2022 https://www.outsideonline.com/health/training-performance/polarized-training-debate/