Week 2: The 80/20 Principle
When new or prospective athletes ask me about my “core training philosophy”, the first thing I always say is “80/20”. About 80% of your training should be at an easy, aerobic effort, with only 20% at moderate to hard intensities. This distribution, validated by research and elite practice, maximizes physiological adaptations while minimizing injury risk and mental burnout. Despite strong evidence supporting this approach, many newer (and less new) runners get it backwards.
Avoiding The Gray Zone
The biggest mistake novice or recreational runners make isn't running hard days too easy—it's running easy days too hard. This creates what exercise physiologists call "gray zone" training: efforts that are too hard for optimal aerobic development but too easy for meaningful anaerobic stimulus.
What Gray Zone Runs Can Look Like:
Easy runs that leave you slightly breathless or unable to hold conversation
"Moderate" paces that feel comfortably hard but not truly challenging
Tempo runs that become red-line races against your training partners
“Recovery day” runs that turn into competitive pace battles
It’s A Trap!: This middle-intensity purgatory feels productive because you're working harder, but it actually sabotages both ends of the training spectrum. You accumulate fatigue that prevents high-quality hard sessions while missing the aerobic adaptations that come from truly easy running.
Breaking the Pattern: Most runners need to dramatically slow down their easy days and significantly intensify their hard days. The gap between these efforts should be substantial and obvious.
The Research Behind the Ratio
The 80/20 principle emerged from observations of elite athletes and is supported by significant research, though the evidence reveals important nuances that merit careful consideration. Multiple studies demonstrate benefits of polarized training, but the picture is more complex than simple advocacy might suggest.
What the Research Shows:
Elite endurance athletes across multiple sports commonly follow distributions where approximately 80% of training occurs at low intensity (< 2 mM blood lactate) with about 20% at higher intensities
Several controlled studies show polarized training can produce superior performance improvements compared to other intensity distributions, particularly for well-trained athletes
Polarized approaches often lead to greater improvements in VO2max and time to exhaustion compared to threshold-focused training
The benefits appear most pronounced in athletes training high volumes (10+ hours per week) and during shorter intervention periods
Important Limitations and Ambiguities: The research contains significant methodological challenges that complicate straightforward conclusions:
Quantification Confusion: Studies vary in how they measure 80/20—some count sessions (any workout with hard intervals = "hard session"), others measure actual time spent in intensity zones. When elite training is analyzed by time-in-zone rather than session goals, distributions often look more pyramidal than polarized.
Context Dependency: Effectiveness varies significantly based on training volume, athlete experience level, and event specificity. Low-volume athletes (under 8-10 hours per week) may not benefit from strict 80/20 adherence, and events contested primarily at moderate intensities may require substantial Zone 2 training.
Individual Variation: Some athletes respond better to different distributions based on genetics, training history, and recovery capacity.
The Physiological Foundation: Easy running drives crucial aerobic adaptations: increased capillary density, mitochondrial development, cardiac stroke volume improvements, and enhanced fat oxidation. These adaptations require substantial training volumes at low intensities. However, the optimal ratio for achieving these adaptations may not be universally 80/20.
Elite Reality Check: When elite training is meticulously analyzed using time-in-zone methods, many successful endurance athletes actually follow pyramidal distributions (high volume easy, moderate volume threshold, low volume high-intensity) rather than strict polarized patterns. This suggests the "80/20" label may be a more pedagogical tool than precise prescription.
Key Research References:
Seiler, S. (2010). What is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? International Journal of Sports Physiology and Performance, 5(3), 276-291.
Stöggl, T. L., & Sperlich, B. (2014). Polarized training has a greater impact on key endurance variables than threshold, high intensity, or high volume training. Frontiers in Physiology, 6, 295.
Filipas, L., et al. (2022). Effects of 16 weeks of pyramidal and polarized training intensity distributions in well-trained endurance runners. Scandinavian Journal of Medicine & Science in Sports, 32(3), 498-511.
They're More Like Guidelines, Anyways
The takeaway from the last section is that the 80/20 rule isn't rigid mathematics nor magic recipe. However, it is a simple and reliable framework for intelligent training distribution. Some weeks might be 90/10 due to recovery needs, others 75/25 when key workouts are scheduled. The monthly average should trend toward 80/20, but weekly flexibility demonstrates smart adaptation, not rule-breaking.
When to Adjust the Ratio:
90/10 or Higher Easy:
Recovery weeks following high-stress periods
Base-building phases early in training cycles
When life stress is elevated (work, family, travel)
During illness recovery or injury comeback
Hot weather or challenging environmental conditions
When in doubt, going with less intensity is almost always best
75/25 or More Intense:
Peak training weeks with multiple quality sessions
Race preparation phases requiring specific adaptations
Not very often
Individual Variation: Your optimal ratio depends on training history, injury susceptibility, life stress, and race distance. Newer runners and high mileage marathoners often benefit from 85/15 or 90/10 distributions, while experienced athletes training for shorter races might handle a sustained 75/25 distribution during peak phases. Some runners may not tolerate the orthopedic stress of high mileage and opt to incorporate significant cross-training; these runners will have a “more intense” appearing distribution of their running if that cross-training isn’t taken into account.
Take The Long View: Focus on monthly and seasonal distributions rather than perfect weekly ratios. A hard workout week followed by an easy recovery week averages out appropriately over time.
Marathon-Specific Application
For marathon training, err on the side of more easy running. High-mileage runners (60+ miles/week) often benefit from 85% or more easy effort. The marathon is fundamentally aerobic—success depends more on your body's ability to utilize oxygen efficiently than on your raw speed.
Why Marathoners Need More Easy Running:
Volume Requirements: Marathon preparation requires substantial weekly mileage to build aerobic capacity and muscular endurance. This volume is only sustainable when most running is genuinely easy.
Specificity Principle: The marathon demands sustained aerobic effort for 2+ hours. Training this energy system requires extensive time spent in aerobic zones—something achieved through easy running, not intense intervals.
Recovery Considerations: Higher training volumes create greater recovery demands. More easy running allows for faster recovery between quality sessions and reduces cumulative fatigue.
Injury Prevention: The orthopedic stress of marathon training is substantial. Easy running provides training stimulus while allowing tissues to adapt and strengthen gradually.
Mental Sustainability: Marathon training cycles last 16-20 weeks. Predominantly easy running prevents mental burnout and maintains enthusiasm for the process.
Practical Considerations
Implementing 80/20 requires both discipline and self-awareness. Most runners intellectually understand the concept but struggle with execution, particularly the discipline required for truly easy running.
Tracking Your Distribution:
Monitor training by time in easy and non-easy zones
Consider using HR zones or RPE (Rate of Perceived Exertion) scales, particularly if you tend to slide into the gray zone
Track weekly and monthly distributions, not just individual sessions
Include warm-ups and cool-downs in your easy percentage calculations
Metrics vs Feel: Pace ranges and accurate heart rate monitoring can help identify time spent in easy and non-easy running zones, but ultimately the most important biometric is “how do you feel?”. Most runners worry about running “too slow” to get any benefit, but in reality that is very hard to do. In general, if your heart rate is above 120 bpm you are getting some aerobic benefit. You should “feel” like you could run that pace for hours while holding a regular conversation, and you should finish that run because you hit a time limit or mileage goal and not because you are too tired to keep going.
Environmental Adjustments: Many factors will impact what pace qualifies as “easy” on a given day. A 45-minute easy run in heat, hills, or wind should be slower than your typical easy pace on a cool, flat route to maintain the same, appropriate effort. Experienced runners learn to hit consistent efforts regardless of external conditions.
A Cautionary Tale on Group Runs: Group runs are great ways to find accountability, socialization, and psychologic benefits. But be wary of impromptu pace competitions that push you to unwittingly violate 80/20 principles. Find run groups and training partners with similar paces and commitment to easy effort, or be willing to run alone when necessary.
Control, Control, You Must Learn Control!: The discipline to run slowly when you feel good is often harder than the discipline to run fast when prescribed. Master this skill, and your marathon training can shift from a constant struggle into a sustainable, enjoyable process that produces breakthrough performances.