Does Exercise Really Reduce Inflammation? A New Study Challenges What We Thought We Knew

Exercise is one of the most consistently recommended ways to improve your health. It can improve cardiovascular fitness, help regulate blood sugar, support weight management, and reduce your risk of developing several chronic diseases.

You've probably also heard that exercise reduces inflammation. It's a claim that gets repeated constantly, especially when people talk about the benefits of walking, Zone 2 cardio, and other forms of lower-intensity exercise.

But does exercise actually lower inflammation, and does the intensity of your workout make a difference?

A new 2026 randomized controlled trial published in the Journal of Science and Medicine in Sport examined exactly that. Researchers compared moderate-intensity and higher-intensity cycling to see how each affected cardiovascular fitness and several inflammatory markers in the blood.

The results were interesting. Both types of exercise improved cardiovascular fitness, but neither produced significant changes in the inflammatory markers measured.

That doesn't mean exercise has no anti-inflammatory benefits. It does raise some important questions about how we measure inflammation, who benefits most, and whether we've been oversimplifying the relationship between exercise intensity and inflammation.

TLDR

A 2026 randomized controlled trial examined whether six weeks of moderate- or heavy-intensity cycling could improve fitness and reduce inflammatory markers in healthy young adults.

• Both exercise intensities improved cardiovascular fitness. Participants increased their peak oxygen consumption and the amount of power they could produce at their lactate threshold.
• Neither intensity significantly reduced the inflammatory markers measured. Researchers found no significant changes in IL-6, TNF-α, or IL-10 after six weeks.
• Higher intensity wasn't better for improving fitness in this study. When exercise energy expenditure was matched, moderate- and heavy-intensity cycling produced similar improvements.
• The participants were already young, healthy, and physically active. Their relatively low baseline inflammation may have limited how much their inflammatory markers could change.
• Six weeks may not have been long enough. Many previous studies reporting reductions in inflammatory markers involved exercise programs lasting longer than eight weeks.
• Blood cytokines don't tell the entire story. Exercise can influence immune cell function and other inflammatory processes without necessarily changing the concentration of specific cytokines in the bloodstream.

The practical takeaway: Don't assume that a workout is better for your health simply because it's described as anti-inflammatory. Both moderate and harder exercise can improve fitness, and the best intensity depends on your goals, current fitness, and ability to recover.

What Is Inflammation, and Why Does It Matter?

Inflammation is a normal and necessary part of your immune system. When you get injured or develop an infection, your body activates inflammatory processes that help fight pathogens, remove damaged tissue, and begin repair.

Without inflammation, you wouldn't recover properly from injuries or respond effectively to infections.

The problem develops when inflammatory activity remains elevated over long periods, particularly when there isn't an obvious injury or infection that needs to be addressed.

This is commonly referred to as chronic low-grade inflammation, and it's associated with several health conditions, including obesity, type 2 diabetes, and cardiovascular disease.

Researchers often evaluate inflammation by measuring proteins in the bloodstream called cytokines. These molecules help immune cells communicate and regulate inflammatory responses throughout the body.

Three cytokines were particularly important in this study.

Interleukin-6 (IL-6) is involved in immune signaling and inflammatory regulation. Chronically elevated resting concentrations can be associated with inflammatory conditions, but IL-6 also has important metabolic and anti-inflammatory signaling roles during exercise.

Tumor necrosis factor-alpha (TNF-α) is a cytokine involved in inflammatory signaling. Elevated concentrations are associated with several chronic inflammatory and metabolic conditions.

Interleukin-10 (IL-10) is generally considered an anti-inflammatory cytokine because it helps regulate and limit certain inflammatory responses.

You might assume that a successful exercise program would reduce IL-6 and TNF-α while increasing IL-10. That's one reason researchers frequently measure these markers when studying the anti-inflammatory effects of exercise.

However, inflammation is much more complicated than simply lowering one cytokine and raising another. The biological effects of these molecules depend on where they're produced, when they're released, and how different cells respond to them.

That distinction becomes especially important when interpreting this study.

How Was the Study Conducted?

Researchers from the University of British Columbia recruited 56 healthy young adults, including 27 men and 29 women, with an average age of approximately 22 years.

Participants were generally healthy and physically active. Individuals with diabetes, cardiovascular disease, certain metabolic conditions, or other factors that could substantially influence inflammatory responses were excluded.

The researchers randomly assigned participants to one of three groups.

Both exercise groups completed three cycling sessions per week for six weeks, totaling 18 scheduled workouts.

One important detail is that the researchers matched the exercise groups for energy expenditure. Men were prescribed approximately 350 calories per session, while women were prescribed approximately 300 calories.

This meant that the harder exercise sessions could be shorter, while the moderate-intensity sessions generally required more time to achieve the same energy expenditure.

The researchers also individualized exercise intensity using each participant's lactate threshold rather than simply prescribing a percentage of maximum heart rate.

That's a meaningful distinction because two people exercising at the same percentage of maximum heart rate aren't necessarily experiencing the same physiological stress.

Before and after the intervention, researchers measured peak oxygen consumption, cycling power at lactate threshold, and fasting blood concentrations of IL-6, TNF-α, and IL-10.

What Is Lactate Threshold, and Why Did the Researchers Use It?

Lactate threshold is a point during progressively harder exercise where blood lactate begins increasing more noticeably above its lower-intensity levels.

It's useful because it helps identify how hard someone can exercise before the metabolic demands become substantially greater.

For this study, the researchers used lactate threshold to separate two exercise intensity domains.

The moderate-intensity group cycled at a power output corresponding to approximately 70% of the power associated with their lactate threshold.

The heavy-intensity group exercised above lactate threshold, using a workload calculated from their threshold and maximum cycling power.

These were continuous cycling sessions, not high-intensity interval workouts. The higher-intensity group maintained a harder workload rather than alternating short sprints with recovery periods.

The difference in actual training intensity was substantial.

The heavy-intensity group had significantly higher heart rates, lactate concentrations, and perceived exertion.

In other words, the harder group really was exercising harder, even though the two groups were matched for estimated energy expenditure.

This allowed researchers to investigate whether the intensity itself influenced the outcomes.

Both Exercise Groups Improved Cardiovascular Fitness

The clearest benefit observed in this study was improved cardiovascular fitness.

After six weeks, both training groups demonstrated significant improvements in peak oxygen consumption, commonly referred to as VO2peak.

VO2peak measures the highest rate of oxygen consumption achieved during a progressively harder exercise test. It's closely related to aerobic fitness and reflects how effectively the cardiovascular and respiratory systems can support exercise.

The researchers found the following changes.

Both groups significantly improved their VO2peak and power at lactate threshold compared with their own baseline measurements.

The heavy-intensity group had a numerically larger improvement in power at lactate threshold, but the difference between the two exercise groups was not statistically significant.

This is an important finding because harder exercise is often assumed to produce better results.

In this study, exercising above lactate threshold didn't produce a statistically greater improvement in aerobic fitness than exercising below it when the prescribed energy expenditure was matched.

That doesn't mean higher-intensity exercise never produces greater improvements. Other training protocols, including interval training, may produce different results.

It does suggest that moderate-intensity exercise can be highly effective for improving aerobic fitness, even when compared directly with substantially harder continuous exercise.

Neither Exercise Intensity Significantly Reduced Inflammation

This was the most interesting finding.

Despite improvements in cardiovascular fitness, neither exercise group demonstrated statistically significant changes in the three inflammatory markers measured.

The researchers evaluated fasting concentrations of IL-6, TNF-α, and IL-10 before and after the six-week intervention.

Here are the estimated changes.

None of these changes were statistically significant, and there were no significant differences between the groups.

The researchers had originally hypothesized that moderate-intensity exercise would reduce inflammatory markers while heavier exercise would not.

That hypothesis wasn't supported by the results.

Both exercise groups improved fitness without measurable changes in fasting IL-6, TNF-α, or IL-10.

It's important to interpret this correctly. The study doesn't prove that exercise has no effect on inflammation. It demonstrates that these particular exercise protocols didn't significantly change these particular blood markers in this population over six weeks.

That's a narrower conclusion, but it's also the scientifically appropriate one.

Why Didn't Exercise Reduce Inflammatory Markers?

There are several possible explanations, and I think the characteristics of the participants are especially important.

The researchers recruited young, healthy adults who were already meeting physical activity guidelines or exercising recreationally.

Their average body mass index was approximately 23.5, and they didn't have known cardiometabolic diseases.

As a result, their baseline inflammatory marker concentrations were generally low.

It's difficult to produce a large reduction in an inflammatory marker when that marker is already low.

Think about it this way. If someone has elevated blood pressure, an exercise program may produce a meaningful reduction. But if their blood pressure is already normal, the same exercise program might improve cardiovascular fitness without substantially changing their resting blood pressure.

A similar concept may apply to inflammatory markers.

Someone with obesity, insulin resistance, or another condition associated with chronic low-grade inflammation may have more room for improvement than a healthy 22-year-old who already exercises regularly.

The researchers specifically acknowledged that their findings might differ in populations with elevated baseline inflammation.

That makes this study useful for understanding exercise responses in healthy young adults, but less informative about what would happen in older adults or people with chronic metabolic disease.

Six Weeks May Not Be Enough to Change Chronic Inflammation

Another possibility is that the intervention simply wasn't long enough.

Six weeks is enough time to produce measurable improvements in aerobic fitness, as this study demonstrated.

However, changes in chronic inflammatory processes may develop over a longer period.

The researchers pointed out that 46 of the 49 studies included in previous meta-analyses examining inflammatory markers used exercise interventions lasting longer than eight weeks.

That's an important difference.

Some benefits of exercise develop relatively quickly, while others depend on longer-term adaptations involving body composition, metabolic health, immune function, and cardiovascular physiology.

For example, regular exercise can reduce visceral fat over time. Since excess visceral fat is associated with chronic inflammatory signaling, reductions in visceral adiposity may contribute to improvements in inflammatory status.

Those changes may require more than six weeks, especially in individuals who don't have much excess body fat to begin with.

However, the researchers didn't directly test whether a longer intervention would have produced different results.

We can say that six weeks didn't significantly change the measured cytokines. We can't say that twelve or sixteen weeks would have produced the same outcome.

Does Higher-Intensity Exercise Cause More Inflammation?

This is where I think the conversation around exercise and inflammation often becomes misleading.

You'll sometimes hear people claim that low-intensity exercise is anti-inflammatory while harder exercise increases inflammation.

There's a small amount of truth behind the idea, but the interpretation is often oversimplified.

A demanding workout can temporarily increase certain inflammatory signals. This is part of the normal physiological response to exercise and doesn't automatically indicate harmful chronic inflammation.

Exercise creates metabolic stress and, depending on the activity, mechanical stress. The body responds through a combination of immune signaling, tissue repair, and adaptation.

Those responses are part of how training works.

An acute inflammatory response following exercise is not the same thing as chronic low-grade inflammation.

For example, IL-6 can increase substantially during prolonged or demanding exercise because contracting skeletal muscle releases it into circulation.

But exercise-associated IL-6 doesn't necessarily have the same implications as chronically elevated resting IL-6 in someone with metabolic disease.

The source, timing, and biological context matter.

This study measured fasting cytokine concentrations after the training intervention, not the immediate inflammatory response during or directly after each workout.

The results therefore don't tell us whether the harder workouts produced larger temporary inflammatory responses.

What they do show is that six weeks of harder continuous exercise didn't produce significantly different resting cytokine concentrations compared with moderate-intensity training.

That's a useful distinction for anyone concerned that exercising harder is automatically harmful because it temporarily increases inflammatory signaling.

Why Blood Tests Don't Tell the Entire Story

One of the more interesting points raised by the researchers is that measuring circulating cytokines may not fully capture changes in inflammatory regulation.

When researchers measure IL-6, TNF-α, or IL-10 in a blood sample, they're measuring the concentration of those molecules at a particular moment.

They aren't directly measuring how effectively immune cells respond to inflammatory signals or how those cytokines function within specific tissues.

It's possible for immune cell behavior to change without a corresponding change in circulating cytokine concentrations.

For example, the researchers discussed previous work showing that exercise intensity can influence how immune cells respond to anti-inflammatory signaling, even when circulating cytokine concentrations don't reflect those differences.

That means a lack of change in blood cytokines doesn't necessarily mean nothing changed within the immune system.

However, this study didn't measure those additional cellular processes, so we can't assume they improved.

The appropriate conclusion is that the measured markers remained unchanged while other aspects of inflammatory regulation were not assessed.

This is also why I tend to be skeptical when someone claims that a particular workout, food, or supplement is anti-inflammatory based on changes in one or two blood markers.

Inflammation is a complex biological process. Reducing it to a single number rarely tells the entire story.

Does This Mean Exercise Isn't Anti-Inflammatory?

No. It means the anti-inflammatory effects of exercise are more dependent on context than many people realize.

Previous systematic reviews and meta-analyses have reported reductions in inflammatory markers following regular exercise, including in populations with cardiometabolic disease.

The authors of this study discussed earlier research showing that exercise can reduce circulating IL-6 and TNF-α, although the magnitude and consistency of those changes vary.

Exercise may influence inflammatory regulation through several pathways, including changes in visceral fat, immune cell populations, inflammatory signaling, and metabolic health.

But not every exercise program will produce measurable reductions in every inflammatory marker, particularly when participants are already healthy.

I think that's an important distinction because exercise is frequently promoted as though it produces the same physiological response in everyone.

A previously sedentary 60-year-old with obesity and insulin resistance is not starting from the same physiological position as a healthy, active 22-year-old.

Both individuals can benefit from exercise, but the specific adaptations may be very different.

This study reinforces the importance of considering who is exercising, what type of exercise they're performing, and which outcomes we're measuring.

Is Moderate-Intensity or High-Intensity Cardio Better for Your Health?

Based on this study, both moderate- and heavy-intensity continuous exercise are effective ways to improve cardiovascular fitness.

When exercise energy expenditure was matched, the researchers found no statistically significant difference in fitness improvements between the two approaches.

The harder sessions required greater effort, but they didn't produce superior improvements in the measured outcomes over six weeks.

That doesn't make higher-intensity exercise useless. It simply means that increasing intensity isn't always necessary to improve fitness.

There are also practical differences worth considering.

Moderate-intensity exercise is generally easier to sustain for longer periods and may be more comfortable for people who are new to structured training or who are managing substantial training volume.

Higher-intensity exercise allows athletes to accumulate a meaningful training stimulus at a greater workload, although it can also produce more fatigue and may require additional recovery.

For someone whose primary goal is general cardiovascular health, consistency and sufficient exercise volume are probably more important than constantly trying to make every workout harder.

For an endurance athlete, the decision becomes more specific. Higher-intensity training can be useful for developing performance at demanding workloads, while easier aerobic training allows athletes to accumulate volume with less fatigue.

This study didn't compare different combinations of training intensities or examine long-term athletic performance, so it shouldn't be used to determine an ideal training distribution.

What it does demonstrate is that meaningful improvements in fitness don't require every workout to be difficult.

What About Zone 2 Training?

Zone 2 has become one of the most popular topics in exercise science, particularly among people interested in longevity, metabolic health, and endurance performance.

Depending on the system being used, Zone 2 generally refers to a relatively comfortable aerobic intensity where the body can sustain exercise for an extended period.

However, there's considerable confusion surrounding the term because different heart-rate and training-zone systems define Zone 2 differently.

In this study, exercise intensity was prescribed relative to lactate threshold rather than a generic five-zone heart-rate model.

The moderate-intensity group exercised below lactate threshold, while the heavy-intensity group exercised above it.

That makes the study relevant to discussions about easier versus harder aerobic exercise, but it wasn't a direct test of a particular commercial or watch-based Zone 2 definition.

The findings support the idea that moderate-intensity aerobic training can improve cardiovascular fitness.

They don't demonstrate that Zone 2 is uniquely anti-inflammatory, and they don't establish that lower-intensity exercise is superior for reducing chronic inflammation.

In fact, neither training intensity significantly changed the inflammatory markers measured.

For most people, I think the practical value of easier aerobic training is straightforward. It allows you to accumulate cardiovascular exercise without every session becoming physically demanding.

That's a useful benefit regardless of whether your blood IL-6 concentration changes after six weeks.

What I Think This Study Actually Teaches Us

I think the biggest takeaway is that improving cardiovascular fitness and reducing circulating inflammatory markers are not necessarily the same thing.

The participants became fitter, but the researchers didn't observe significant changes in IL-6, TNF-α, or IL-10.

That doesn't make the training ineffective. It means the adaptations occurred without measurable changes in those particular markers.

The study also challenges the assumption that moderate-intensity exercise is inherently more anti-inflammatory than harder exercise.

When the researchers compared two different exercise intensities while matching energy expenditure, neither approach significantly changed the inflammatory markers.

I also think the study illustrates why context matters so much when interpreting exercise research.

Healthy, active young adults may respond differently than people who have elevated baseline inflammation or chronic metabolic conditions.

And six weeks of training may produce different outcomes than six months.

The absence of a measurable change in one biological marker shouldn't automatically outweigh clear improvements in physical fitness.

That's especially true when the marker represents only one part of a much more complicated physiological system.

How Should You Apply This Research?

For someone exercising primarily to improve general health, I wouldn't make major changes based on this study.

Regular aerobic exercise remains an effective way to improve cardiovascular fitness, and both moderate- and higher-intensity training can contribute to those improvements.

A reasonable approach is to build a routine around exercise you can perform consistently, then adjust intensity according to your fitness level, goals, and recovery.

A few practical considerations are worth keeping in mind:

• Prioritize consistency. Three manageable workouts every week will generally be more useful than an overly aggressive program you struggle to maintain.
• Don't assume harder is always better. Moderate-intensity exercise produced similar improvements in aerobic fitness in this six-week trial when energy expenditure was matched.
• Use higher intensity when it serves a purpose. Harder workouts can be valuable for performance, but they don't need to dominate every training session.
• Don't judge your exercise program by one inflammatory marker. Cardiovascular fitness, exercise capacity, and other health outcomes provide important information that a single cytokine measurement cannot capture.
• Consider your starting point. Someone with elevated baseline inflammation may respond differently than the healthy young adults included in this study.

For endurance athletes, the same general principles apply. A combination of easier aerobic training and appropriately programmed harder sessions can support performance, although this particular study doesn't establish the best combination.

And for people who are primarily concerned about chronic inflammation, it's worth remembering that exercise is only one factor influencing inflammatory health.

Body composition, metabolic health, sleep, diet, and underlying medical conditions can also influence inflammatory processes.

The goal should be improving overall health rather than trying to manipulate a single laboratory value.

Important Limitations of the Study

Although this was a randomized controlled trial with carefully prescribed exercise intensities, there are several limitations.

First, the participants were young, healthy, and already physically active. The findings may not apply to older adults, sedentary individuals, or people with obesity, diabetes, or other conditions associated with elevated inflammation.

Second, the intervention lasted only six weeks. That was enough to improve aerobic fitness, but it may not have been sufficient to produce detectable changes in circulating cytokines.

Third, the researchers measured only three cytokines: IL-6, TNF-α, and IL-10. These are relevant markers, but they don't provide a complete picture of inflammatory activity or immune cell function.

Fourth, the study was designed around detecting changes in VO2peak, not primarily powered to identify small differences in inflammatory markers between exercise groups. A larger sample may have detected effects that this trial could not.

Finally, the researchers compared moderate- and heavy-intensity continuous cycling. They didn't examine resistance training, sprint intervals, longer training programs, or different combinations of exercise intensities.

These limitations are important because the results shouldn't be interpreted as evidence that exercise has no anti-inflammatory benefits.

The study answers a specific question about six weeks of continuous cycling in healthy young adults, and its conclusions should remain within that context.

The Bottom Line

A 2026 randomized controlled trial examined whether six weeks of moderate- or heavy-intensity continuous cycling could improve fitness and alter circulating inflammatory markers in healthy young adults.

Both training approaches significantly improved peak oxygen consumption and cycling power at lactate threshold.

However, neither exercise intensity significantly changed fasting IL-6, TNF-α, or IL-10 concentrations, and the researchers found no meaningful differences between the exercise groups.

These findings don't contradict the broader evidence supporting regular exercise for long-term health. They demonstrate that improved fitness doesn't always coincide with measurable changes in specific inflammatory markers, particularly over relatively short training periods in already healthy individuals.

I wouldn't use this study as a reason to avoid harder exercise, and I certainly wouldn't interpret it as evidence that moderate-intensity cardio doesn't work.

The most important takeaway is that exercise intensity should be selected based on your goals, preferences, and recovery needs rather than unsupported claims that one intensity is automatically more anti-inflammatory than another.

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

McCarthy SF, Jackson GS, Islam H, Little JP. Six weeks of isocaloric moderate- and heavy-intensity continuous training improves fitness but does not alter plasma cytokines in healthy young adults. Journal of Science and Medicine in Sport. 2026. https://doi.org/10.1016/j.jsams.2026.08.207.