Polarized Training: Is It the Best Way to Boost Endurance Performance?

You've probably heard about polarized training—it’s a training method emphasizing mostly easy efforts (zone 1), a sprinkle of high-intensity workouts (zone 3), and minimal moderate-intensity runs (zone 2). It's gained huge popularity among runners aiming to break performance plateaus, but how does it stack up scientifically against other training intensity distribution models?

​A recent scoping review tackled this very question, comparing polarized training against pyramidal (70% zone 1, 20% zone 2, and 10% zone 3), threshold (45–50% zone 1, 45–50% zone 2, and 5–10% zone 3), and block training models. The researchers systematically reviewed 15 studies that examined long-term effects on physiological markers and performance outcomes across different athlete levels—from recreational runners to elite competitors.

Polarized and pyramidal approaches came out ahead for maximal oxygen uptake (VO2 max), showing superior improvements. These models prioritize substantial easy running (zone 1) combined with targeted, high-intensity sessions (zone 3), and both approaches maximize aerobic adaptations.

Polarized and pyramidal models also showed significant gains in speed and power at the aerobic threshold (think: your comfortable but brisk "all-day" running pace), meaning they’ll help you run at higher speeds with less effort—a critical element for distance running.

Interestingly, all training intensity distribution models proved effective for improving anaerobic threshold–-crucial for running fast for shorter durations, like a 10-kilometer race or a finishing kick in longer events. There wasn’t enough evidence to definitively say one model is superior for improving running efficiency (how much oxygen you consume at a given speed).

What this means for runners

Polarized and pyramidal models appeared to offer distinct advantages for elite and highly competitive runners—those aiming to squeeze out every possible performance gain.

For recreational and lower-level runners, the differences between training models seemed less critical, indicating that consistency in training matters most. Whichever training model you choose, keeping most of your training genuinely easy and periodically going hard seems to optimize endurance adaptations, regardless of the label you give your training model.

RELATED ARTICLE: Our Guide To Polarized Training: Keep Easy Runs Easy and Hard Runs Hard​

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Can Blackcurrant Extract Reduce GI Distress on Hot Runs?

Gastrointestinal symptoms during exercise, especially in hot conditions, are common and can derail your training and races. And as the summer approaches, it’s worth thinking about strategies to limit tummy trouble during sweltering runs. According to a new study, a simple dietary supplement could ease these symptoms.

Researchers examined whether taking New Zealand blackcurrant extract (which you can find some more information on here), rich in anthocyanins (the compounds that give berries their vibrant colors), could alleviate exercise-induced gastrointestinal discomfort in the heat.

They recruited 12 recreationally active men, all reasonably fit, with an average VO2 max of 56 mL/kg/min. Participants took either the blackcurrant extract or a placebo daily for seven days before running for an hour in hot conditions (about 93°F/34°C).

With the placebo, nearly everyone (92%) experienced some gastrointestinal (GI) discomfort—belching, side stitches, bloating—but after just one week of taking blackcurrant extract, this number dropped dramatically to only 25%. More specifically, the total severity score of GI symptoms was cut nearly in half. Upper GI issues (like belching or reflux) were most notably reduced, dropping from 75% with placebo to just 25% with the supplement. Even lower GI symptoms (like cramps or urgent bathroom trips) showed improvement.

What this means for runners

If you're prone to GI distress during hot runs, experimenting with anthocyanin-rich supplements like New Zealand blackcurrant extract could provide significant relief. A daily dose of approximately 210 mg of anthocyanins (as tested in this study) taken for at least a week before intense heat exposure seems beneficial. However, while blackcurrant extract helps, combining it with gradual heat acclimatization and good hydration strategies will likely yield the best results. In any case, it’s a supplement strategy that’s probably low risk and high reward if you’re willing to experiment.

RELATED ARTICLE: 10 Tips To Avoid Unplanned Bathroom Breaks At Your Next Race​

Calorie Deficits Change the Way Your Body Uses Fuel During Exercise

All runners know they need to fuel their workouts adequately. But what happens when you're in a calorie deficit—whether intentionally cutting weight or inadvertently under-eating during intense training blocks? Can your body still effectively use the carbs you take during exercise, or does performance suffer? New research gives us a clear look at what happens when athletes operate on reduced calories.

Researchers tested how different levels of short-term calorie deficit (20%, 40%, and a substantial 60%) affect the body's ability to burn carbohydrates consumed during exercise. Participants first ate normally for four days, then entered a six-day period of reduced calorie intake at varying levels. At the end of each dietary phase, they hopped on a stationary bike for a 90-minute moderate-intensity ride while sipping on a glucose drink, immediately followed by a ride-to-exhaustion test to measure endurance.

Regardless of how severe the calorie deficit, participants consistently burned slightly less of the glucose they consumed during exercise—about a 10% reduction compared to when they were fully fueled. Interestingly, muscle glycogen stores (your muscles' fuel tanks) were also noticeably lower during calorie deficits, reinforcing the idea that being under-fueled—even for just a few days—can alter how your body manages energy.

Despite these metabolic shifts, participants didn't perform any worse in the exhaustion test, even in the most extreme (60%) calorie deficit. Essentially, their bodies adapted remarkably well, maintaining performance despite being slightly less efficient at burning incoming carbs.

What does this mean for runners?

Your body is surprisingly robust in managing short-term energy shortages without performance loss. A brief calorie deficit won't necessarily ruin your next workout or race, but let’s be careful about extrapolating these findings to the long term, where training and performance will likely suffer. Even though your body burns fewer carbs when under-fueled, consuming carbohydrates during workouts is still essential. They help sustain performance by supporting blood sugar levels and sparing muscle glycogen.

The bottom line: A few days of inadequate fueling might not make or break a training session or a race—so don’t stress about it. Just don’t make it a habit.

RELATED ARTICLE: Can You Build Muscle In A Calorie Deficit?​

HERE’S WHAT ELSE YOU WOULD HAVE RECEIVED this week if you were a subscriber to the complete, full-text edition of “Run Long, Run Healthy.” SUBSCRIBE HERE.

• Could a simple jump rope be the key to faster running?

• Minimalist footwear and foot exercises for improving performance and strength

• Why being less flexible is an advantage for masters athletes
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​Thanks for reading. As always—Run Long, Run Healthy
​​
~Brady~