Polarized Base Training: Key to Success (#8)

We won't go unnecessarily deep, but simply put: your body excels at what it's exposed to. The question is how you can best stimulate your body to maximize your potential. Jacob Gudiol has written an excellent article that describes the two common models, GAS (General Adaptation Syndrome) and FF (Fitness Fatigue). If you want to read more about the models themselves, we refer you to his blog. In this article, we'll show why you should polarize your training—meaning how you can incorporate high-intensity training into milder training blocks, and vice versa—to get the most out of your season.

If you have a Garmin, Polar, or Suunto watch, you're familiar with the classic zones 1–5. They were developed by the Norwegian Olympic Committee and have become a standard in most heart rate monitors. To keep it simple, we'll use three zones instead of five here.

In simple terms:

• Study zone 1 = your watch's zone 1 and 2: easy pace.
• Study zone 2 = your watch's zone 3 and 4: faster pace and race pace.
• Study zone 3 = your watch's zone 5: above threshold, often beyond race pace (unless you're an 800-meter runner — who wants to be that, it just hurts).

You've probably heard phrases like "rack up miles on your legs" or "time on the clock" more than once. Is there more to it than just wisdom from seasoned pros?

In a review from 2010, P. B. Laursen and colleagues highlight that while low-intensity training may show subtle effects in short studies, elite endurance athletes typically spend about 75% of their training time in the low-intensity zone (zone 1). This intensity is kept below the first ventilatory threshold. Few studies demonstrate short-term performance improvements when volume is increased—possibly because the study durations aren't long enough to show significant effects.

Laursen also mentions a fascinating retrospective study where researchers examined the training of 21 highly successful rowers from 1970 to 1990. These studies compared training development with competition results and physical capacity without altering the training regimen.

Over these 20 years, the rowers’ VO2max improved from 5.8 to 6.5 liters/min, and training volume increased from 30–50 hours/month. Meanwhile, the time spent at or above competition pace decreased from 23 to 7 hours/month. The athletes shifted from mostly high-intensity training to spending only 14% at competition pace, while their annual volume escalated from 924 to 1,128 hours/year. Although the rise in low-intensity training isn't fully explained, it's reasonable to conclude that the benefits of increased volume outweigh the downsides of higher intensity, such as increased injury risk and overtraining.

The effects are transferable to recreational athletes with low training volume (about 2–3 sessions/week), making it relevant beyond elite athletes.

70/20s, 8×2 minutes, 4×4 minutes, 6×1,000 meters, and so forth—a beloved training tool goes by many names. High-intensity workouts have solid evidence supporting performance enhancement, and we suspect you've tried at least one of these gems at some point. None of them are magical on their own—choose based on your goal—but all are designed to really elevate your heart rate and push your body to adapt.

It turns out that 4×4 is a type of interval where many find it easy to push their heart rate up to 90-95% of the maximum. This might explain why cyclists and skiers prefer intervals in 3-5 minute sets, while runners often opt for 1,000-meter repeats. The key is to get your heart rate over 90% of max.

A total work time of around 30 minutes, like 4×8 minutes (32 minutes), has been shown to be more effective than the classic 4×4, which results in 16 minutes of total work time, even though the intensity is higher with 4×4 (95% for 16 minutes vs. 90% during 4×8 minutes). We don't think one is unequivocally better than the other. The aim is to be in zone 3 and above the threshold. With 4×4, you can train at a higher intensity, stressing the muscles more, while 8-minute intervals are easier on the legs as you maintain a slightly slower pace. Just different tools in the same toolbox.

The same study also evaluated 4×16 minutes and observed less impact than 4×4. Likely because the intensity was at the threshold and not above, unlike the 4- and 8-minute intervals.

Is there a purpose to those long, demanding sessions like 8×9 minutes or 5×5 km that many marathon runners do? Absolutely—they're more race-specific, and because the intensity is lower, they should be reserved for closer to race season. It's these intervals now (if you're a summer athlete) that will set the pace for longer threshold and tempo runs as the season approaches.

Okay, you're planning to crush your intense intervals every week — but hold on a sec.

In studies, they've explored how to boost the impact of interval training even further. What if you didn't see a week as a seven-day stretch but rather as part of a 12-week block? Then, one week could be a hardcore interval week, while the other weeks are more low-intensity. By not just polarizing on a weekly basis but also blocking intensity over several weeks, you can achieve faster and greater improvements.

In a 12-week study, well-trained cyclists were split into two groups, both with the same total training volume but different interval distributions:

1. Five interval sessions in one week followed by three weeks with one interval session per week (for one group).
2. Two interval sessions per week (for the other group).

Results: Both groups improved, but the group that periodized their intervals and had an interval week every fourth week improved the most. The difference was significant: an 8.8% increase versus a 3.7% increase in oxygen uptake for the group that blocked an interval week. Should you stop with 2 interval sessions a week? Absolutely not. But feel free to experiment with blocking your tough intervals to specific weeks.

In a well-conducted study from 2013, well-trained cyclists (PPO 4.7 W/kg) followed two different training regimens:

1. 80% of training was around or under zone 1 and 20% in zone 3. This included 6×4-minute intervals at 5–10% above threshold.
2. 55% in zone 1 and 45% in zone 2. In this regimen, zone 2 was reached by maintaining an intensity between zone 1 and zone 3 for 60 minutes—above endurance pace but below tough intervals. Participants in the study were previously accustomed to classic 75/25 training (usually 53% zone 1, 38% zone 2, and 9% zone 3).

The study highlighted that the volume in zone 1 was carefully controlled, and the main difference between the groups was the amount spent in zone 2 versus zone 3. After the training period, the greatest improvement was seen in participants who followed the polarized regimen (80% in zone 1, 20% in zone 3).

Training only in zones 1 and 3 might sound extreme, so here's our emphasis: If you aim to boost your physical capacity, your ceiling, high-intensity intervals combined with easy distance sessions seem to be most effective. This doesn’t mean that training at race pace is harmful—rather, you need to incorporate race-specific training at the right time in your schedule.

One reason polarized training is effective is that training at race pace or sub-threshold stresses the body similarly to higher intensity, but with lower benefits in terms of improved VO2, movement economy, and more, while carrying a higher risk of negative impacts see ref..

One of the most intriguing effects was that the first threshold (the boundary to zone 2) increased with polarized training. This means that the pace you can maintain during low-intensity sessions improves without specifically training at that pace. Many skilled endurance athletes consistently show that they can move quickly while still feeling comfortable, whereas others end up in zone 3.

It might seem confusing that the Norwegian ski team does 60-minute intervals while someone else just does Tabata. The fact is, we often start from different levels: some athletes predominantly engage in low-intensity workouts, while others focus almost exclusively on high-intensity, short sessions. If you can only manage 2–3 sessions a week, it's best to maximize the ones you can do—a couple of intervals and one long session. If you prioritize training and can schedule up to five sessions or more per week, the effects of a distinct polarized approach can be quite powerful.

With a weekly training time of around five hours or more, we recommend focusing on the bigger picture and zooming out. There will be periods when you might only have time for short lunch sessions, and this is sufficient to maintain your capacity — at least as long as the intensity is high.

1. If you can dedicate five hours or more to training per week, ease off on your endurance and circulation sessions. Elite athletes spend about 80% of their training in zone 1, and the benefits become clearer over time. It's a perfect chance to also refine technique and feel good simultaneously.
2. Train intensively 20% of the time, ideally above the lactate threshold. The type of interval depends on the purpose, but 4×4 is a format that many can push themselves hard with both physically and mentally, and receive substantial stimulation from. Even longer cumulative work durations, like 4×8 minutes, are very effective—just make sure you get over the threshold.
3. Avoid zone 2 during base training unless you're preparing specifically for a competition. The body seems to get as fatigued from this type of intensity as from high-intensity intervals, but without the same positive effects on VO2 max, movement economy, and muscle strength.
4. Block certain weeks designed for intervals to get even more pronounced effects. Dare to zoom out and plan the base season with tougher blocks—it yields results.
5. Consistency, consistency, consistency. Few plans work if you don't stick to them. We've highlighted what leads to measurable physical improvements. That doesn't mean it's wrong to only do easy endurance sessions or solely intensive spinning classes—this is more like a nudge to think outside the box and create a training schedule that better fits your goals.