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. doi.org/10.1371/journal.pone.0154075
