What Type of Cardio Is Best for Fat Loss? A New Study Compared HIIT, Threshold, and Polarized Training

When people want to lose body fat, cardio advice usually goes in one of two directions. One group says you should do longer, easier workouts because lower intensities burn a greater percentage of fat. The other says high-intensity interval training is better because you can work harder and burn more calories in less time.

There is some truth buried in both arguments, but the type of exercise that burns the most fat during a workout is not automatically the type that produces the most body-fat loss over several weeks. How much total exercise you can perform, how well you recover from it, and whether you can consistently repeat it all matter.

A 2026 randomized study compared three very different ways of organizing aerobic training in previously untrained young women with obesity. Researchers compared high-intensity interval training, threshold training, and polarized training, which combined a large amount of easier aerobic exercise with a smaller amount of very hard exercise.

All three approaches worked. However, polarized training produced the largest improvements in body weight, fat mass, aerobic fitness, and several measures of metabolic health.

That does not mean we have suddenly discovered the perfect fat-loss workout. The study was small, short, and conducted in a very specific population. Still, I think it teaches us something useful about how cardio can be structured, especially for someone who is currently sedentary and trying to improve both body composition and health.

TLDR

Researchers divided 40 previously untrained young women with obesity into four groups and followed them for 10 weeks. Three groups exercised three times per week using either HIIT, threshold training, or polarized training, while the fourth group served as a non-exercising control.

• All three exercise programs reduced body weight and fat mass.
• Polarized training produced the largest reduction in body weight, dropping from 83.7 kg to 81.0 kg, or about 2.7 kg.
• Fat mass decreased from 38.5 kg to 37.1 kg with polarized training, a reduction of about 1.4 kg.
• HIIT reduced body weight by about 1.2 kg and fat mass by about 0.5 kg.
• Threshold training reduced body weight by about 1.1 kg and fat mass by about 0.5 kg.
• Polarized training produced the largest improvement in VO2max and generally greater improvements in several cardiovascular and metabolic measurements.
• The polarized program spent approximately 75% of training time at low intensity and 25% at high intensity, with almost no time in the middle.
• The study does not prove polarized training is universally the best exercise for fat loss. There were only 10 participants per group, all were young women with obesity, and the intervention lasted only 10 weeks.
• The practical takeaway is that you probably don't need to make every cardio session hard to get good results. Plenty of easier aerobic work combined with a smaller dose of hard training may be a very effective approach.

What Is Polarized Training?

Polarized training is common in endurance sports, but someone exercising primarily for weight loss may never have heard the term. The concept is fairly simple: most aerobic training is performed at a relatively easy intensity, a smaller amount is performed very hard, and relatively little time is spent in the uncomfortable middle.

In this study, researchers established three exercise zones using each participant's ventilatory thresholds. These are physiological points where breathing and metabolism begin changing as exercise becomes progressively harder. The lower zone worked out to roughly 65% to 67% of maximum heart rate, the middle zone was around 81% to 82%, and the highest zone was around 92% to 93%.

The polarized group performed approximately 75% of its weekly exercise time in the easiest zone and 25% in the highest zone, with almost no deliberate training in the middle zone. The HIIT group performed its prescribed exercise work at high intensity, while the threshold group split its training approximately evenly between the lower and middle zones.

This is quite different from how many recreational exercisers train. They often spend a lot of time somewhere in the middle, working hard enough that the session creates considerable fatigue but not hard enough to provide the same stimulus as true high-intensity intervals. Polarized training separates those jobs by keeping easy training easy and hard training genuinely hard.

How Was the Study Conducted?

The researchers recruited 40 women between 19 and 23 years old with a BMI between 25 and 40 kg/m². They were considered untrained because they had been performing less than two hours of physical activity per week.

Participants were randomly assigned to one of four groups: polarized training, HIIT, threshold training, or a non-exercising control group. Each group contained 10 participants, and the exercise groups completed three supervised sessions per week for 10 weeks, giving them 30 training sessions.

The researchers assessed much more than weight loss. They measured body mass, fat mass, fat-free mass, VO2max, ventilatory thresholds, resting heart rate, blood pressure, maximal cardiac output, stroke volume, fasting glucose, cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides.

This is one reason I find the study more interesting than simply asking which workout burned the most calories. The researchers could see how different ways of organizing exercise affected body composition, cardiovascular fitness, and metabolic health at the same time.

All Three Types of Cardio Reduced Body Fat

There was no useless exercise group in this study. After 10 weeks, body weight and fat mass decreased in all three exercise groups, while the control group essentially stayed the same.

The differences between the groups are easier to appreciate when you look at the actual numbers.

The polarized group lost approximately 2.7 kg, or 6 pounds, of total body weight over the 10 weeks. By comparison, the HIIT group lost about 1.2 kg and the threshold group lost approximately 1.1 kg.

The fat-mass results followed the same pattern. The polarized group lost approximately 1.4 kg, or 3.1 pounds, of measured fat mass, compared with about 0.5 kg in both the HIIT and threshold groups.

Those are meaningful differences, but they also need some context.

Exercise Alone Produced Fairly Modest Fat Loss

The polarized group clearly performed the best for body composition, but losing about 3 pounds of measured fat over 10 weeks isn't some unbelievable transformation. In fact, that is one of the more useful lessons from this research.

Exercise is extremely valuable for health and can absolutely contribute to fat loss, but exercise by itself usually isn't the most powerful tool for creating a large calorie deficit. Food intake gives you much more direct control over how much energy is coming into the body.

That doesn't make cardio unimportant. Exercise increases energy expenditure while also improving fitness, cardiovascular health, glucose regulation, and many other things that simply eating fewer calories cannot accomplish.

The two strategies have different jobs. Nutrition can help create the calorie deficit needed for fat loss, while exercise can increase energy expenditure and improve the health and fitness of the body losing that weight.

Trying to force exercise to do everything usually isn't the best approach.

Why Might Polarized Training Have Worked Better?

The most obvious feature of polarized training is the large amount of lower-intensity work. At easier exercise intensities, the body can rely heavily on fat oxidation to provide energy, but that doesn't necessarily mean this was the reason the group lost more body fat.

I think the more interesting explanation is how much useful exercise someone can accumulate without overwhelming their ability to recover. Lower-intensity aerobic exercise creates a much smaller recovery cost than repeatedly performing very hard intervals, which makes it possible to accumulate more sustainable training.

The smaller amount of high-intensity work then provides a different stimulus. Hard intervals challenge the cardiovascular system and can drive improvements in VO2max, stroke volume, cardiac output, and exercise capacity.

Putting the two together gives you a relatively large amount of sustainable aerobic work combined with a smaller but potent dose of high-intensity training. You don't have to choose between easy cardio and hard cardio because they can serve different purposes within the same program.

That may be one reason polarized training worked so well in this study.

More Intensity Isn't Automatically Better

HIIT gets marketed heavily for weight loss because it sounds efficient. If working harder burns more calories per minute, it seems logical that harder exercise should always produce better results.

The problem is that calories burned per minute isn't the only variable that matters.

Imagine you can comfortably perform 45 or 60 minutes of easier aerobic exercise, but you can only tolerate 15 or 20 minutes of legitimate high-intensity intervals. The harder workout may require more energy per minute, but that doesn't automatically mean it creates greater total energy expenditure.

Recovery also matters. If extremely hard cardio makes you less active for the rest of the day, interferes with your strength training, increases soreness, or makes you less likely to train tomorrow, some of the theoretical advantage disappears.

This doesn't mean HIIT is bad. The HIIT group in this study lost weight, lost fat, and substantially improved cardiovascular fitness. It simply means that making a workout harder does not automatically make it better.

For most people, the better program is the one that provides enough training stress to create adaptation while still allowing them to recover and consistently repeat the work.

Polarized Training Produced the Largest Increase in VO2max

Fat loss wasn't the only advantage seen with polarized training. All three exercise groups improved VO2max, which reflects the body's maximal ability to take in, transport, and use oxygen during exercise.

The HIIT group increased VO2max from 27.8 to 30.7 mL/kg/min, while the threshold group increased from 28.2 to 30.9 mL/kg/min. Both were substantial improvements after only 10 weeks.

The polarized group did even better, increasing from 28.3 to 32.7 mL/kg/min. That's an improvement of approximately 4.4 mL/kg/min, compared with 2.9 for HIIT and 2.7 for threshold training.

This is important because cardiorespiratory fitness is a valuable health outcome independent of what happens on the scale. Someone who loses only a modest amount of weight while becoming substantially fitter may have accomplished far more for their health than their body-weight change suggests.

The Cardiovascular Benefits Went Beyond VO2max

Researchers also measured ventilatory thresholds, maximal cardiac output, stroke volume, resting heart rate, and blood pressure. All three exercise programs improved several measures of cardiovascular fitness, but polarized training generally produced the largest changes.

Resting heart rate provides a simple example. The polarized group went from approximately 75.8 beats per minute to 70.9, while HIIT decreased from 75.5 to 73.1 and threshold training decreased from 75.8 to 73.2.

The polarized group also showed larger improvements in maximal stroke volume and cardiac output. These measurements tell us something about how effectively the heart can deliver blood and oxygen during demanding exercise, and their improvement helps explain the larger increase in VO2max.

Blood pressure, however, did not significantly change. That's worth mentioning because a successful exercise intervention doesn't necessarily improve every health marker over a relatively short period.

Glucose and Cholesterol Improved Too

The researchers also measured several metabolic health markers. Fasting glucose, total cholesterol, LDL cholesterol, and triglycerides decreased across the exercise groups, while HDL cholesterol did not significantly change.

Polarized training generally produced larger adaptations than HIIT or threshold training across these measurements. Combined with the improvements in cardiovascular fitness and body composition, this is why the results are more interesting than simply saying one group lost a few more pounds.

Obesity management shouldn't be reduced to the number on a scale. Someone can improve cardiorespiratory fitness, resting heart rate, glucose regulation, cholesterol, triglycerides, and exercise capacity even when the change in body weight isn't dramatic.

That is one of the biggest reasons exercise remains valuable during weight loss.

Does Low-Intensity Cardio Burn More Fat?

This study gives us a good opportunity to clear up one of the oldest cardio arguments. At lower exercise intensities, a greater percentage of the energy being used generally comes from fat. As exercise intensity increases, carbohydrate becomes increasingly important as a fuel source.

That physiology is real, but burning more fat during a workout does not automatically mean losing more stored body fat over several weeks. Fat loss depends on what happens to energy balance over a much longer period.

You could perform a long, easy workout and burn plenty of fat during the session, then consume enough calories afterward to replace everything you used. Conversely, you could burn proportionally more carbohydrate during a harder workout while still losing body fat because your total energy expenditure exceeds your energy intake over time.

This is why the popular "fat-burning zone" can be misleading. The percentage of workout energy coming from fat is not the same thing as the amount of body fat you will eventually lose.

Does This Mean Zone 2 Is Best for Fat Loss?

Not exactly. In fact, interpreting this study as evidence that everyone should only perform Zone 2 cardio would miss one of its most important features.

The polarized group performed most of its training at low intensity, but approximately 25% of its exercise time was performed at very high intensity. The strategy that performed best wasn't all easy cardio. It was mostly easier training combined with a smaller amount of genuinely hard work.

There is also a terminology problem when discussing exercise zones. The researchers defined their zones using individually measured ventilatory thresholds, so their Zone 1 isn't necessarily identical to what your smartwatch, treadmill, or favorite fitness app calls Zone 1 or Zone 2.

The broader principle is much more useful than obsessing over the label. Most aerobic training can be performed at an intensity that feels sustainable and recoverable, while a smaller amount can be used to provide a strong high-intensity stimulus.

What Might This Look Like in the Real World?

I wouldn't take this study and conclude that everyone needs exactly 75% easy cardio and exactly 25% high-intensity training. Even the researchers pointed out that studies of endurance athletes often find considerably smaller percentages of high-intensity exercise.

For an everyday active adult, the concept can be much simpler. Someone performing three cardio sessions each week might make two of them mostly easy aerobic sessions and use the third for intervals or another form of harder aerobic work.

The easier sessions could involve brisk walking, incline treadmill walking, easy running, cycling, rowing, swimming, or an elliptical. The specific activity matters less than whether you can control the intensity, perform enough work to create a useful stimulus, and recover well enough to do it consistently.

As fitness improves, the volume can gradually increase. There is no reason every cardio workout needs to turn into a competition with yourself.

What About Strength Training?

This study only compared aerobic exercise programs, so it cannot tell us whether polarized cardio is better than resistance training for changing body composition. That's an important distinction when discussing the "best exercise" for fat loss.

I generally wouldn't choose between cardio and resistance training anyway because they serve different purposes. Aerobic exercise can increase energy expenditure and dramatically improve cardiovascular fitness, while resistance training provides a strong stimulus for maintaining or increasing muscle mass.

Preserving muscle becomes particularly important when someone is intentionally eating fewer calories. If your goal is to improve body composition rather than simply make the number on the scale smaller, keeping resistance training in the program makes sense.

A well-designed fat-loss plan can therefore include resistance training, aerobic exercise, and plenty of general daily movement rather than forcing one type of exercise to do everything.

Don't Forget About Walking and Daily Activity

Formal workouts are only one part of how much energy you use during the day. Walking around at work, taking the stairs, cleaning the house, shopping, doing yard work, playing with your kids, and simply spending less time sitting all contribute to total daily energy expenditure.

This is another reason I don't love fat-loss programs built entirely around brutal workouts. If someone performs an exhausting exercise session and then spends the rest of the day sitting because they're wiped out, the workout may not create as large an increase in total daily energy expenditure as expected.

A program that allows you to train while still remaining active throughout the rest of the day may be more useful. The goal isn't to burn as many calories as possible during a 30-minute workout. The goal is to build a lifestyle that keeps total activity high enough to support your body-composition goals.

There Are Important Limitations to This Study

Before declaring polarized training the undisputed king of fat loss, there are several reasons to be cautious. The study included only 40 participants, meaning each group contained just 10 women. Small studies can identify interesting differences, but the results need to be repeated in larger populations before we assume the same advantage will always appear.

The participants were also very specific. They were young women with overweight or obesity who had previously been exercising less than two hours per week. We don't know whether the same differences would appear in men, older adults, trained athletes, or people who already perform regular aerobic exercise.

The intervention lasted only 10 weeks, so the study cannot tell us whether polarized training would maintain its advantage over six months, a year, or longer. Training intensity was also monitored primarily through heart rate, and the researchers acknowledged that the actual weekly training volume may not have been perfectly matched between groups.

Body composition was measured using bioelectrical impedance analysis, which can be influenced by hydration and other factors. I wouldn't treat every tenth of a kilogram in the reported fat-mass changes as perfectly precise, even though the overall direction of the results is still useful.

These limitations don't erase the findings, but they should stop us from turning one study into a universal rule.

What I Think This Study Actually Teaches Us

I don't think the main lesson is that everyone trying to lose weight needs to become a polarized endurance athlete. The more useful lesson is that you probably don't need as much hard exercise as you think.

There is a tendency to assume a workout only counts if you're breathing hard, sweating heavily, and exhausted afterward. That mentality can turn every cardio session into the same uncomfortable grind and eventually make exercise harder to recover from and less enjoyable to perform.

Polarized training takes a different approach by accumulating plenty of manageable aerobic work and then using a smaller amount of high-intensity exercise to provide a stronger fitness stimulus. That structure may allow someone to accumulate more useful exercise without creating as much fatigue as repeatedly performing hard workouts.

For someone who is currently sedentary, this may be especially valuable. Starting with several HIIT workouts every week is unnecessary when a combination of easier aerobic exercise and strategically placed hard sessions can produce substantial improvements.

Nutrition Still Matters More Than Most People Want to Admit

No discussion about fat loss is complete without talking about food. You can build an excellent exercise program and still fail to lose meaningful body fat if your energy intake consistently matches or exceeds your energy expenditure.

Exercise can increase calorie expenditure, improve insulin sensitivity, improve cardiovascular health, preserve fitness, and make long-term weight maintenance easier. Those are all important reasons to exercise, even if weight loss is not the primary goal.

However, nutrition usually gives you considerably more control over the calorie deficit required for fat loss. Trying to burn off hundreds of extra calories through increasingly difficult workouts is often less practical than making reasonable changes to food intake.

For most people, I would rather combine a manageable calorie deficit with resistance training, plenty of daily movement, and an aerobic program they can actually recover from. Exercise should support the fat-loss plan rather than become punishment for eating.

The Bottom Line

This 10-week study compared HIIT, threshold training, and polarized aerobic training in previously untrained young women with obesity. All three approaches reduced body weight and fat mass while improving cardiovascular fitness and metabolic health, but polarized training generally produced the largest improvements.

The polarized group lost approximately 2.7 kg of body weight and 1.4 kg of measured fat mass, compared with about 1.1 to 1.2 kg of body weight and 0.5 kg of fat mass in the HIIT and threshold groups. It also produced the largest increase in VO2max and generally stronger improvements across several cardiovascular and metabolic measurements.

What makes the result interesting is how the training was organized. Approximately 75% of the polarized group's training was performed at a relatively easy intensity, while about 25% was very hard. They didn't make every workout difficult, but they also didn't rely exclusively on easy cardio.

If you're trying to lose fat, I wouldn't obsess over finding one magical cardio intensity. Build most of your aerobic volume at an intensity you can sustain and recover from, include a smaller amount of harder work, resistance train to help preserve muscle, remain active throughout the day, and use nutrition to create the calorie deficit.

That's probably a better long-term strategy than trying to make every workout as hard as possible.

About the Author

Matt Mosman, MS, CISSN, CSCS, is the founder and Chief Science Officer of Simply Good Supplements. With a background in exercise science, sports nutrition, and strength and conditioning, Matt focuses on turning research into practical advice that athletes, parents, and everyday active people can actually use.

References

Zhou C, Teng Y, Xu Y. Adaptive Responses of Cardiorespiratory Fitness and Cardiometabolic Risk Factors to Polarized Versus Other Types of Training Intensity Distribution in Obese Untrained Females. Journal of Sports Science and Medicine. 2026;25:395–404. doi:10.52082/jssm.2026.395.