The Polarization Index (P.I.)

Endurance athletes and coaches often talk about polarized vs. non-polarized training. But what does this actually mean, and how can you quantify whether a training program is polarized or not? A new metric called the polarization index (PI) aims to provide some clarity.

The polarization index is a simple calculation that looks at the distribution of your training time or distance across three intensity zones:

  • Zone 1: Low intensity
  • Zone 2: Medium intensity
  • Zone 3: High intensity

To determine the PI

PI = log10(((Zone 1 / Zone 2 )* Zone 3) * 100)

If your PI is greater than 2.00, your training distribution is considered polarized. This means the majority of your training volume is spent in Zone 1, with less emphasis on Zones 2 and 3. Non-polarized training distributes volume more evenly across the three zones.

Research has shown that elite endurance athletes tend to follow a polarized training model. Their high volume of low intensity training allows them to absorb the hard workouts and adapt to get stronger. But what PI is ideal? There is no perfect number, as it depends on your specific sport and goals. The PI simply quantifies your polarization.

So in summary, the polarization index is an easy way to calculate whether your training is polarized or not based on time or distance in three intensity zones. It provides an objective measure you can track over time as you refine your training plan for optimal performance. Give it a try!

You can find the PI index in the activity analysis and in the calendar view of the SELFLOOPS website.


Treff, G., Winkert, K., Sareban, M., Steinacker, J. M., & Sperlich, B. (2019). The Polarization-Index: A Simple Calculation to Distinguish Polarized From Non-polarized Training Intensity Distributions. Frontiers in physiology10, 707.

Unlock Your Athletic Potential: Training in Zone 2 and Comparing Polarized and Pyramidal Training

For athletes, maximizing sports performance is the ultimate goal. Achieving peak performance involves a combination of dedication, discipline, and employing intelligent training methods.

One crucial aspect of training that often gets overlooked is understanding and harnessing your training zones.

At Selfloops, we’ve incorporated the Time in Zones charts that empower athletes and coaches to track and analyze the time spent in different training intensity zones (based on heart rate, power, or speed).

You can visualize the Time in Zones for various types of activities or as a cumulative measure across all activities performed. Additionally, you can customize the start and end dates for these charts.

In this blog post, we will delve into the concepts of training in Zone 2 and explore the differences between the polarized and pyramidal approaches to zone training. Our aim is to equip you with the tools needed to optimize your athletic journey.

The Importance of Training Zones

Endurance coaches, athletes, and scientists devote considerable effort to determining the ideal blend of training session intensity, duration, and frequency to achieve desired physiological adaptations in athletes and to maximize their performance during key competitions. This process, known as training periodization, involves varying these variables throughout a training cycle.

To deepen our understanding of training analysis, a range of training intensity zones has been identified. These zones are determined by physiological metrics such as lactate threshold, ventilatory thresholds, percentage of maximum oxygen uptake, percentage of maximum heart rate, or subjective criteria like perceived exertion levels.

The concept of training intensity distribution (TID) refers to the amount of time an athlete spends in different training intensity zones during an exercise. These zones provide structure to workouts and ensure that you train at the right intensity to effectively achieve your goals.

Zone 2: The Foundation for Athletes

One of the most critical training zones for athletes is Zone 2.

Zone 2 is commonly referred to as the aerobic zone. It represents a moderate intensity level where your body primarily relies on aerobic metabolism, utilizing oxygen to produce energy. Zone 2 concludes at the first aerobic threshold, such as the first ventilatory threshold or lactate threshold.

Zone 2 training is essentially about elevating your heart rate sufficiently and maintaining it for an extended duration to build aerobic fitness without reaching the point where you gasp for breath. It is the intensity level where you start to notice a shift in your breathing patterns. A simple way to identify your aerobic threshold, without a lab test, is when you transition from speaking comfortably in extended paragraphs to only managing short sentences. At this stage, you are still relatively comfortable, and you could likely sustain this effort for an extended period, although it is important to recognize that you are indeed engaged in meaningful exertion. This training is also known as aerobic training or base training.

Benefits of Training in Zone 2

  • Improved Aerobic Capacity: Zone 2 training enhances your body’s efficiency in utilizing oxygen, enabling you to sustain exercise for longer durations, ultimately leading to better endurance in your chosen sport.
  • Enhanced Fat Utilization: Training in Zone 2 encourages your body to burn fat for fuel, which can aid in weight management and benefit long-duration events where carbohydrate stores may become depleted.
  • Reduced Risk of Overtraining: Zone 2 training is generally low in intensity, making it an excellent choice for active recovery or lighter training days. This helps prevent overtraining, reducing the risk of injuries and burnout.

Polarized vs. Pyramidal Approaches to Zone Training

Two popular training approaches that utilize training intensity distributions are the polarized and pyramidal methods. Let’s delve into these concepts in more detail below.

In this context, we consider the training intensity distribution based on three training zones: Z1 (below the first ventilatory threshold VT1), Z2 (between the first and the second ventilatory threshold VT2), and Z3 (above the second ventilatory threshold).

Polarized Training:

Polarized training is a method that emphasizes spending the majority of your training time at low intensity, with the remaining time dedicated to high intensity. It places less emphasis on the intensity zone between the two extremes (low and high intensity). This approach aims to maximize the benefits of both low-intensity aerobic development and high-intensity anaerobic power. In Polarized training, the intensity distribution is characterized by the highest percentage of time spent in Z1, a smaller yet relatively high percentage in Z3, and only a small portion of training in Z2.

In Polarized training Z1 > Z3 > Z2

Typically, it involves around 80% of training at low intensity (Z1), 5% at middle intensity (Z2), and 15% at high intensity (Z3).

Benefits of Polarized Training:

  • Improved aerobic capacity and anaerobic power.
  • Enhanced recovery due to the abundance of low-intensity training.

Pyramidal Training:

Pyramidal training, in contrast, places more emphasis on a balanced distribution across intensity zones. When considering three intensity zones (low, middle, high), pyramidal training allocates the most time to the first zone, with progressively less time spent in the other zones. The pyramidal training intensity distribution is characterized by a higher percentage of training time in Z1, less in Z2, and even less in Z3.

In a Pyramidal Training Z1> Z2 > Z3

Typically, it involves around 80% of training at low intensity (Z1), 15% at middle intensity (Z2), and 5% at high intensity (Z3).

This approach provides a well-rounded foundation for overall fitness and can be particularly beneficial for athletes who engage in various sports or events.

Benefits of Pyramidal Training:

  • A balanced approach addressing multiple aspects of fitness.
  • Suitable for athletes with diverse training goals.
  • Reduced risk of overemphasizing a single energy system.


Understanding your training zones and incorporating Zone 2 training into your routine can significantly enhance your sports performance. Whether you choose the polarized or pyramidal approach, both methods offer their advantages and can help you achieve your athletic objectives. Remember that consistency and personalized training are key; what works best for one athlete may not be the ideal strategy for another. Consulting with a coach or sports scientist to tailor your training zones and methods to your specific needs is crucial, allowing you to witness your athletic performance reach new heights.


  • Seiler, S., & Kjerland, G. Ø. (2006). Quantifying training intensity distribution in elite endurance athletes: Is there evidence for an “optimal” distribution? Scandinavian Journal of Medicine & Science in Sports, 16(1), 49-56. doi: 10.1111/j.1600-0838.2004.00418.x
  • 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. Doi: 10.1123/ijspp.5.3.276
  • Iñigo San Millán Zone 2 Link
  • Deep dive back into Zone 2 Training with Iñigo San-Millán link
  • SimplaVida, Zone 2 Training
  • Jason Koop, Koopcast Polarized vs Pyramidal Training with Luca Filipas PhD | Koopcast Episode 113
  • Valenzuela PL, Morales JS, Foster C, Lucia A, de la Villa P. Is the Functional Threshold Power a Valid Surrogate of the Lactate Threshold? Int J Sports Physiol Perform. 2018 Nov 20:1-6. doi: 10.1123/ijspp.2018-0008.
  • Stöggl T, Sperlich B. Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Front Physiol. 2014. doi:10.3389/fphys.2014.00033
  • Stöggl TL, Sperlich B. The training intensity distribution among well-trained and elite endurance athletes. Front Physiol. 2015. doi:10.3389/fphys.2015.00295
  • Treff G, Winkert K, Sareban M, Steinacker JM, Sperlich B. The polarization-index: a simple calculation to distinguish polarized from non-polarized training intensity distributions. Front Physiol. 2019. doi:10.3389/fphys.2019.00707
  • Treff G, Winkert K, Sareban M, Steinacker JM, Becker M, Sperlich B. Eleven-week preparation involving polarized intensity distribution is not superior to pyramidal distribution in national elite rowers. Front Physiol. 2017. doi:10.3389/fphys.2017.00515
    • Neal CM, Hunter AM, Brennan L, et al. Six weeks of a polarized training-intensity distribution leads to greater physiological and performance adaptations than a threshold model in trained cyclists. J Appl Physiol. 2013; 114(4): 461-471. doi:10.1152/japplphysiol.00652.2012
  • Muñoz I, Seiler S, Bautista J, España J, Larumbe E, Esteve-Lanao J. Does polarized training improve performance in recreational runners? Int J Sports Physiol Perform. 2014; 9(2): 265-272. doi:10.1123/IJSPP.2012-0350
  • Filipas, Luca, et al. 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 (2022): 498-511. doi: 10.1111/sms.14101
  • Esteve-Lanao, J., San Juan, A.F., Earnest, C.P., Foster, C. and Lucia, A., 2005. How do endurance runners actually train? Relationship with competition performance. Medicine & Science in Sports & Exercise, 37(3), pp.496-504. doi: 10.1249/01.mss.0000155393.78744.86

SELFLOOPS Now Syncs with Apple HealthKit

We are thrilled to announce the newest update to the SELFLOOPS Spark app for iPhone and Apple Watch. With this update, we are bringing you a game-changer in health and fitness data management – the ability to seamlessly sync your Apple HealthKit data with SELFLOOPS. Let’s dive into the details of this exciting development.

Your Health and Fitness Data, All in One Place

The SELFLOOPS Spark app now enables you to effortlessly synchronize your health and fitness metrics stored in your iPhone and Apple Watch with the SELFLOOPS website. This means that data such as your daily step count, sleep patterns, resting heart rate, and workouts performed using the Apple Watch workout app can be automatically synced to your Selfloops account.

This seamless integration streamlines your data management, providing you with a holistic view of your health and fitness journey.

Why is This a Game-Changer?

Data Integration: We are making it easier than ever for you to consolidate your health and fitness information. Whether you are tracking your steps, monitoring your sleep, or recording your workouts with your Apple Watch, all this valuable data will now reside in a single repository – your Selfloops account.

Streamlined Sharing: Athletes, coaches, and fitness enthusiasts will appreciate the enhanced sharing capabilities. This feature allows you to effortlessly share your data with your coach, providing them with the insights they need to tailor your training plan for optimal results.

Future-Proof: Our commitment to continuous improvement means that we are not stopping here. In the future, we plan to add more HealthKit metrics to the list of synchronized data sources. This means that you will have even more comprehensive insights at your fingertips.

How to Get Started

Getting started with the SELFLOOPS Spark app and Apple HealthKit synchronization is easy:

Update Your SELFLOOPS Spark App: Ensure you have the latest version of the SELFLOOPS Spark app installed on your iPhone.

  • Enable the HealthKit Integration: Navigate to the settings of the Spark iPhone app and select the “Health” option. From there,  grant the required HealthKit access rights, then select the metrics you want to synchronize.
  • Automatic Synchronization: Your health and fitness data will now automatically sync with your SELFLOOPS account. You can access and analyze this data on the SELFLOOPS website.

Taking Your Health and Fitness to the Next Level

With this powerful new feature, SELFLOOPS Spark empowers you to export your data and perform in-depth analysis using the advanced tools available on the SELFLOOPS website ( Whether you are an elite athlete, a dedicated fitness enthusiast, or simply someone who wants to keep a close eye on their health, having all your data in one place allows for a more comprehensive and insightful understanding of your progress.

At SELFLOOPS, we are committed to helping you achieve your health and fitness goals. With the Spark app and its integration with Apple HealthKit, we are making it easier than ever to track, analyze, and optimize your journey. Stay tuned for future updates as we continue to expand our features, ensuring you have access to the latest advancements in health and fitness technology.

Introducing Automated Workout Synchronization for Stages Cycling

We are happy to announce the new feature that allows seamless synchronization of your Stages Cycling workouts. Now, you can effortlessly transfer all your workout data from Stages Cycling devices and apps to Selfloops, providing you with a comprehensive fitness tracking experience.

Whether you prefer using a Stages bike computer or the Stages smartphone app, you can now have your valuable workout information securely stored on the Selfloops website. Activating this integration is simple. Just follow these steps:

  1. If you have a Stages bike computer or are using the Stages smartphone app, navigate to the “Connections” section in the Stages app.
  2. Look for Selfloops in the list of available connections and select it.
  3. Once selected, you will be redirected to the Selfloops website to log in. In case you don’t have an account yet, you can easily sign up for one there.

Once you have successfully logged in, all your future workouts completed with Stages devices and apps will be automatically synchronized with Selfloops. This means that you no longer have to manually transfer your data between platforms or worry about missing any crucial workout information.

By streamlining the synchronization process, we aim to enhance your fitness journey and provide you with a consolidated overview of your performance. With Selfloops and Stages Cycling working together seamlessly, you can focus on achieving your fitness goals without any hassle.

Improving Sports Performance: The Importance of Tracking Overall Feeling

Sports performance is highly influenced by our daily state of mind and well-being. Each day brings a unique set of circumstances, with some days brimming with energy and others where our mood may not be at its best. Recognizing this, we have introduced a new metric called “Overall Feeling” to enhance our understanding of sports performance and empower coaches and athletes to make improvements.

To include the Overall Feeling metric in an athlete’s calendar, simply navigate to the desired day and click the “+” sign. From there, select “Add Metric” and choose “Overall Feeling.” Additionally, our smartphone apps now offer the convenience of adding this metric on the go. The scale ranges from 1 (Horrible) to 10 (Best), allowing individuals to easily quantify their emotional state.

These metrics can be analyzed within the Health section and the Trends section of the Selfloops website. In the Trends section, users have the ability to correlate the Overall Feeling metric with other valuable indicators, such as the Session RPE (Rate of Perceived Exertion).

The Overall Feeling metric serves as an expression of an athlete’s mood on a specific day. In addition to this, we have also introduced the “How do you feel?” metric within an activity log, focusing on an athlete’s post-workout experience.

While external load, which can be measured through heart rate monitors and bike power meters, provides insight into an athlete’s physical strain, internal load is gauged through the “How do you feel?” metric and the Rate of Perceived Exertion (RPE).

By integrating sports performance metrics like bike power or heart rate with the feeling/mood metric and RPE, coaches and athletes gain a more comprehensive understanding of an athlete’s overall form and fitness level.

It’s important to recognize that our feelings and mood significantly impact our performance. With the inclusion of these metrics, we offer coaches and athletes an additional tool to effectively track, analyze, and optimize sports performance.