Moderate Intensity Exercise Improves Immune Function While High Intensity Interval Training (HIIT) Reduces Immunity

Just when you thought the only acceptable way to exercise these days is with high intensity intervals (HIIT) we have some new data that suggests good old moderate intensity cardiovascular training is not only just as good, it may be better for your immunity.

Just when you thought the only acceptable way to exercise these days is with high intensity intervals (HIIT) we have some new data that suggests good old moderate intensity cardiovascular training is not only just as good, it may be better for your immunity.

While there is plenty of data supporting the benefits of HIIT, as you dig through the research comparing HIIT to more moderate intensity training you can find studies that support HIIT, others that favor moderate intensity and still more that show similar effects. With the publicity that HIIT training has received over the past few years (including in this blog) and the facilities that are built around it you might be left thinking that despite the limited and mixed research on the topic, you have to be banging out heart wrenching workouts at the local boutique gym in order to make any gains.

Today we have a study that suggests when you are talking about the effect of your exercise routine on immunity, you may be better off with more moderate intensity workouts.

The authors had half of their subjects run high intensity intervals for multiple rounds of 30 seconds at 100% intensity and then 30 seconds at 50% intensity. The moderate intensity group did an equivalent amount of work, but it was performed continuously at 75% intensity.

At the end of 9 weeks all the various physiological factors that were measured showed similar results with one major exception, immune biomarkers. The specific biomarkers were all white blood cells leukocytes, lymphocytes, neutrophils and monocytes. The high intensity training group saw negative changes in all four of these key immunity markers while the moderate intensity training group saw positive improvements.

These findings fall in line with previous studies that have found a suppression of immunity with high intensity training and others that have shown improvements with more moderate intensity approaches.

As I always caution, with every study there are limitations. This study only had 16 subjects and they were all fit, active young men ages 18-20. While it would seem logical that if this population saw these types of changes everyone else would, there is no data to say the same results would be found with women or with other age groups or people with different health status. There is also the question of what would be different if the study was of a different length of time, the training frequencies were different, or the training volumes were greater.

What does this study mean for you, the average exerciser or fitness professional? Well we know that many people find high intensity workouts uncomfortable and unenjoyable. This means a much great chance of their stopping exercise, something we obviously don’t want to happen. So, anytime we find some evidence suggesting that more moderate intensity training is just or good or better than the highly publicized high intensity approaches that supports ignoring the buzz and letting people skip the HIIT.

Certainly there are still times that certain fitness training objectives require higher training intensities, but for the average exerciser they can probably skip the intervals if they don’t enjoy or tolerate them. And if someone is dealing with any sort of illness or medical condition in which optimizing their immunity is a key factor, skipping the high intensity work in favor of other approaches just may be the safest and best approach.


Khammassi, M., Ouerghi, N., Said, M., Feki, M., Khammassi, Y., Pereira, B., Thivel, D. and Bouassida, A. (2020) Continuous Moderate-Intensity but Not High-Intensity Interval Training Improves Immune Function Biomarkers in Healthy Young Men. Journal of Strength and Conditioning Research. January, 34:1:249-256.

Sprint Interval Training Leads To Improved Results With A Five-Fold Lower Amount Of Time And Volume

You can’t turn on your computer or glance at your phone these days without seeing an article about how high Intensity interval training (HIIT) is the activity you must be doing to get fitter. We’ve covered some of the benefits in previous posts and pretty much every fitness professional worth their weight in protein powder is preaching HIIT. The problem has been for all the data that has accumulated recently regarding the benefits of interval training, very little research has directly compared it’s impacts against more traditional approaches towards exercise.

The reason why, this research is complicated and time consuming to conduct and there are only so many resources that are allocated to the topic. Today we have a study that shows for some important measures of cardiometabolic heath, interval training can provide similar benefits to longer duration moderate intensity cardiovascular training in 20% of the time.

Considering that lack of time is one of the major factors that people site for not meeting their exercise goals an approach that provides meaningful benefits in a short period of time could be an optimal solution for some. The exercise guidelines of 150 minutes of moderate intensity or 75 minutes of vigorous intensity aerobic activity a week are well established and accepted. If you can cut those numbers back considerably while still maintaining meaningful cardiometabolic changes then there may be a large segment of the population that can benefit while overcoming their time restraint barriers.

The Study

Sprint interval training (SIT) is a version of HIIT that involves very brief bursts of all-out intensity followed by longer periods of low-intensity recovery exercise. Compared to HIIT, the intervals are generally shorter and harder and the recovery periods longer. In this study SIT was compared to moderate intensity continuous training (MICT), think jogging or riding the bike for a longer period of time at a comfortable but slightly strenuous pace.

The SIT group performed a 2-minute cycling warm up followed by three 20 second all-out cycling intervals. Each interval was followed by a 2-minute low-intensity recovery effort. The final recovery interval was a 3-minute cool down. The total time spent on the bike was 10 minutes per session and only 1 minute of it was full intensity sprint work.

The MICT group cycled for 45 continuous minutes at approximately 70% of the maximum heart rate. They had an additional 2 minute warm up and 3-minute cool down for a total of 50 minutes of work per session. There was also a control group that did not exercise.

In the first week of the study the subjects exercised 1 time. In the second week they exercised twice and for the following 10 weeks they exercised 3 times per week. At week 7 and at the conclusion of the 12 weeks they were assed.

Cardiorespiratory Fitness

Both the SIT group and the MICT group experienced a 19% improvement in their VO2peak over the course of the 12 weeks. At 6 weeks both groups had already achieved a 12% increase. That is a significant improvement in a relatively short period of time and similar achievement between both the SIT and MICT suggests both the time saving effect of the SIT approach but also the value of the MICT for individuals who may not be able to train at the intensity levels necessary for SIT.

Glycemic Control

The more insulin sensitive someone is, the better job their cells do of removing sugars from the blood stream. Poor insulin sensitivity can lead to high blood sugar levels and ultimately type 2 diabetes. It has been well accepted that physical activity is an effective means to improve insulin sensitivity over time. In this study the SIT group saw a 53% improvement in their insulin sensitivity over 12 weeks. The MICT group also saw an impressive 34% improvement. While both results are outstanding clearly the SIT intervention was superior.

Skeletal Muscle Mitochondrial Content

Mitochondria are the powerhouses of our cells and the more we have, the more energy we can produce. It is widely accepted that mitochondria production increases with physical activity, specifically exercise that is aerobic in nature, including high-intensity interval training. Measuring the activity level of the enzyme citrate synthase is a method of determining the mitochondrial content of skeletal muscle. Over the 12 weeks the SIT group in this study saw a 48% increase in maximal activity of citrate synthase while the MICT group had a 27% increase.

Putting it all together

The body of research demonstrating the effectiveness of various interval training techniques continues to grow. This study very clearly demonstrates that SIT is as effective as MICT in improving cardiorespiratory fitness, insulin sensitivity and skeletal muscle mitochondrial content. The SIT actually showed better results then more traditional training. The most interesting aspect of all of this is that the SIT protocol required a five-fold lower volume and time of exercise to achieve the same results. Just 1 minute of peak work within a 10-minute period, 3 times a week was enough to match 3 sessions of 50 minutes of MICT per week.

Now don’t think that you can just suddenly start training hard for very short periods of time regardless of your training status and objectives. This study showed positive changes with that approach and when we are talking about improving health measures the improvement is significant. If you are a higher-level athlete pushing your fitness levels toward peak levels you will still require more training, but for most average people, the lower volumes are exceptionally interesting. The higher-level athlete still can look at higher intensity training techniques, but they will be applied differently. For weight loss, both groups in this study saw a positive change in body composition but the purpose of the study was not to examine optimum approaches to body fat loss. We will cover that in other posts.

There is also the issue of how many individuals can train at SIT levels of intensity. Individuals new to exercise, older individuals and those with various physical limitations or disease states may not be able to perform SIT. For some it is a physical issue, for others a motivational one. More traditional moderate-intensity training is still valid and appropriate for many populations but for those who are looking for a shorter time commitment, SIT might just be the ideal intervention to improve their health and fitness.


Gillen, J., Martin, B., MacInnis, M., Skelly, L., Tarnopolsky, M. and Gibala, M. (2016) Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment. PLOSOne: April 26.