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Performance Impacts of Periodization and Training Intensity Distribution

A November 2021 study uses a fascinating research design to test different types of periodization over a 16-week training cycle.

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A primary offset between training theory and exercise physiology studies is the time horizon problem. What works over a few days, a few weeks, a few months, and a few years can be completely different. That offset sometimes sends athletes down counter-productive paths.

Consider high-intensity interval training. You may have heard of “Tabata intervals,” a workout usually consisting of repetitions of 20 seconds hard with 10 seconds easy recovery. The protocol was part of a 1996 study in the Medicine and Science in Sports and Exercise journal, where participants did what we now call Tabatas (named after the study author) five times per week for 6 weeks. Their VO2 max increased nearly 10% and their anaerobic capacity increased 28%. 25 years later, you can still find Tabatas in plenty of training programs. (Meanwhile, doing “Roches” involves going through 3 boxes of cereal in 2 days.)

It’s now settled that approaches to HIIT like those 20-second sprints would likely reduce aerobic performance over longer time horizons, with short-term gains in some athletes offset by an erosion of the aerobic foundation. When we say “the aerobic system,” we mean an interconnected series of adaptations to muscle fibers, the metabolic system, and oxygen processing, all of which operate on longer time scales and are the dominant influences on all performances over a couple minutes. 

Tabatas take that aerobic system and light it on fire. But like all fires, eventually you’ll run out of logs. Zoom out, and most HIIT-focused programs end up making tough, strong, inefficient athletes.

You can see that reflected in the training that elite athletes actually perform outside the lab. For example, a 2019 study in the Journal of Strength and Conditioning Research looked at 85 elite athletes over their first seven years of serious training, finding that volume of easy running had the highest correlation with performance, rather than super-high-intensity sessions. The time horizon offset is a result of it being really hard to design studies that track participants long-term while controlling for variables in a meaningful enough way to draw conclusions.

That’s why my new favorite study is one that just came out in the Scandinavian Journal of Medicine and Science in Sports, with a research team led by Luca Filipas. It zooms out longer-term to confront a question that has been immensely difficult to answer in prospective, intervention-based studies. The question: How do different types of training periodizations (varying interventions over time) impact performance over a training cycle? 

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Study Design

Put yourself in the shoes of the study authors–how do you even start to answer that type of question? You’d need a ton of participants to discern the signal from the noise. You’d need a way to standardize different groups to track changes. And you’d need to sustain interventions for long enough to get past the initial changes that can happen with any new workout. I’m exhausted just thinking about all of the moving parts it would require.

The study authors absolutely rocked it. They recruited 60 well-trained male runners (it would be great to have the study design replicated with female athletes, and Dr. Filipas indicated on Twitter that they are trying to start a similar study in well-trained female runners). They divided them into four different groups of periodization techniques, controlling for baseline attributes. They had a 6-week pre-intervention period to add more certainty to the starting point, then gathered training data for 16 weeks, long enough to see changes across a full training cycle. 22 weeks of training changes in 60 advanced athletes! Heck yes! 

Best of all? You can imagine how fitness changes over the 16-week intervention period might extrapolate to a year or longer, so they’re really getting at some fundamental questions of training theory. My co-coach Megan and I go into more detail on our podcast episode that comes out today.

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Periodization Overview

A 2010 review article in Sports Medicine outlined the frontiers of periodization theory, involving dividing a training season into smaller units of distinct focuses. By layering one focus on top of another, athletes can use smaller training units (microcycles of days/weeks working into mesocycles of weeks/months) as building blocks, developing specific strengths and then using those strengths to develop new strengths while avoiding stagnation. However, best practices with periodization are hotly debated–get 20 coaches and exercise physiologists in a room to discuss periodization, and there would likely be some VO2 max-intensity disagreements.

The different periodization techniques analyzed in the 2021 study were based on training intensity distribution via a 3-zone model. A 2015 review article in Frontiers of Physiology outlined that most endurance training is in Zone 1, defined as below the first ventilatory threshold. At those lower intensities, lactate levels are stable below 2 mM–think about the 80%+ Zone 1 training for elite cross country skiers. Zone 2 is more moderate, often approaching traditional “lactate threshold” training–think controlled tempos and some cruise intervals or steadier running. Zone 3 is harder–think fast intervals and harder hill work.

In the new study, training minutes in those 3 zones are the building blocks for testing 2 periodization techniques:

  • The first is “Polarized” training. Polarized training involves mostly going easy or hard–more time in Zone 3 than Zone 2 (harder intervals over moderate tempos).
  • The second is “Pyramidal” training. Pyramidal training involves more moderate than hard–more time in Zone 2 than Zone 3 (moderate tempos over harder intervals). 

Both approaches still have the bulk of time in Zone 1 (while much is up for debate, the science is settled on the value of mostly aerobic training for endurance athletes). A 2018 review article in the International Journal of Sports Physiology and Performance examined another type of periodization (threshold training, which includes much more time in Zone 2, often greater than 20%). It found the most effectiveness for Polarized and Pyramidal models, with the caveat that some of the best marathoners in the world focus on threshold training.

The study separated the 60 athletes into 4 groups for the 16-week period:

  • Pyramidal training only;
  • Polarized training only;
  • 8 weeks Pyramidal training (lower intensity) to 8 weeks Polarized training (higher intensity); and
  • 8 weeks Polarized training to 8 weeks Pyramidal training.

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Training Methods

There was a 6-week pre-intervention period of 250-350 minutes of weekly training, followed by initial testing. Training volume was constant for all athletes to avoid measuring fitness increases from added load. They took down weeks every 4 weeks. Athletes entered data into the software program Training Peaks and included heart rate info.

Looking at the training plans, Pyramidal weeks were 15% to 17% zone 2 and 6% to 7% zone 3. That usually consisted of one zone 3 interval session like 12 x 2 minutes or 4 x 7 minutes, one one session of 40 to 55 minutes in zone 2. 

Polarized weeks were mostly 6% to 7% zone 2 and 14 to 15% zone 3. That meant two harder interval sessions most weeks. 

Honestly, they’re really good training plans even outside the specific aims of the study. The authors should call Table 1 “8 Weeks To Your Fastest Half Marathon” and sell it for $100 a month.

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Study Results

The big finding: changing the type of periodization appeared to be effective, primarily by improving running economy. Let’s focus on the 5k performance changes, ranking them from best to worst (note: there are error bars in all of these numbers, so for the purposes of this discussion, take them as approximate guidelines to consider some broader principles):

  • Pyramidal to Polarized: 1.5% improvement
  • Polarized only: 1.1% improvement
  • Polarized to Pyramidal: 0.9% improvement
  • Pyramidal only: 0.6% improvement

Digging into the results more, there seems to be a fascinating (though not surprising) response to Polarized training (remember, Polarized training involves more high intensity work). The Polarized-only group, for example, had over 80% of their improvement in the first 8 weeks. The Pyramidal-only group had only half their improvement in that time. 

Now pay attention here, because this is what I consider the money finding. The Polarized to Pyramidal group had closer to 100% of their improvement in the 8 weeks of polarized training. The Pyramidal to Polarized group had less than a third of their improvement in the first 8 weeks. In other words, Polarized training seems to light a fuse–use it too early, and improvement may stagnate, at least in shorter races like a 5K. But it’s important to use or you’ll never get all you can out of performance.

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The authors have a terrific perspective, noting that the Polarized training could enhance a “peaking”-like response when completed closer to testing off of a more Pyramidal base. However, “peaking cannot be explained by a single value; rather, it is the result of a combination of muscular, cardiovascular, hormonal and psychological factors derived from high intensity training, which act in synergy to maximize training adaptations.” In training, we’re throwing a lot of ingredients into the stew, and the final taste isn’t determined by the exact ratio of carrots or beans, but by a complex interrelationship that does not have a single, universally-applicable answer.

There are three elements of this study that I will remember for the rest of my coaching life. If you can’t tell, I’m already sad to never again get to read this study for the first time. My current soundtrack is “Time of Your Life” by Green Day like it’s a high school graduation in 2003.

One: Varying training stimuli in mesocycles can be beneficial, but be careful how you stack it.

Periodization works by accruing adaptations, then using those adaptations to accrue more adaptations. It’s a lot like compound interest–a base period of mostly zone 1 running lets you get more out of zone 2 and zone 3 running, and that faster running makes your zone 1 running more efficient, and on and on. The study found that top-end zone 3 adaptations likely stall out over time (to some extent at least). So it’s good to mix up focuses within training cycles, but save an emphasis on very intense training until you have the fitness to use it. And when you use that fitness to fuel zone 3 training, USE IT with intention. 

Training takeaway: before adding a secondary intense workout, consider adding more volume or tempo running unless you’re approaching the specific phase for a shorter event, or a speed phase that may lie mid-cycle in training for a longer event like a marathon or ultra.

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Two: Intensity can be a fast-acting drug.

Three of the four groups did a Polarized training block. In the first 8 weeks of Polarized training, each group improved between 0.9% and 1.1%, the highest totals in the study. One of the groups added another Polarized training block on top of it (the Polarized-only group). That group only added ~0.3% to the total. So you may not need a super-long focus on multiple intense workouts a week to achieve many of the adaptations–I’d be curious to see if we could design a program where that 1% improvement comes in just a few weeks. And I bet that those adaptations eventually stagnate (or possibly reverse) entirely. That’s one theory for why athletes ran so fast when races started after the pandemic–they spent months focusing less on intense workouts, then lit the fuse on a much bigger base when races restarted.

Training takeaway: consider inserting small blocks of more intense training, rather than longer, more intense cycles, particularly when training for longer events. As long as top-end speed/output is maintained, an athlete can almost never have too much aerobic base.

Three: Different athletes respond differently, so pay attention to individual responses and individual goals.

While the average performance increases in the study were striking, not every athlete improved the same way. Some even got worse from the most effective training interventions! And while 5k performance likely has some correlation with different distances, it’s possible that an athlete building peak fitness for a 5k may actually be less aerobically and metabolically efficient for a marathon or ultra. If I could have been a rogue study author, what I would have done is have the groups race a marathon to cap it all off. I’d then change my name and move to Uzbekistan because the Ethics Board would have a bounty on my curious ass.

Would the Pyramidal group that underperformed in the 5k excel in the marathon? And maybe most importantly, what would happen in 2 years–would the Pyramidal group steadily improve cycle after cycle? Who gets injured more? All of the groups had some zone 3 intensity–what if you take that out entirely? Would female athletes respond differently?

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Training takeaway: specific training closer to events on top of a big base is probably still the most important principle in periodizing training cycles. For example, if you’re racing a marathon, you should be very comfortable at marathon pace in the pre-race mesocycle, with more intense workouts purely supporting adaptations that help marathon pace feel relaxed. But those specific adaptations likely matter well before you get toward a peaking phase.

Notably, even these periodized models of varying intensity involve mostly easy running. Make sure you start there–build that aerobic base, and do some fast strides for the neuromuscular and biomechanical adaptations to turn base into sustainable speed. 

From there, the world is your oyster or your chicken tender, depending on your feelings on shellfish. Mix in threshold, do some faster work, and have fun. Just make sure you aren’t putting multiple hard sessions per week at the forefront of your focus year-round, or eventually, you may find that your speed falls through the floor from a termite-infested foundation.


David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things), and they wrote a book called The Happy Runner.

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