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Can 1 Minute of All-Out Exercise 3 Days a Week Improve Your Cardiovascular Fitness and Blood Glucose/Insulin Levels?

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Thursday, Jul 13, 2017

High-intensity interval training, also known as HIIT or sprint interval training (SIT), involves alternating short bouts of maximal intensity effort with low intensity recovery periods within the same workout.  One appealing aspect of SIT workouts is that they do not last nearly as long as traditional ‘steady state’ workouts where the individual maintains a constant level of moderate intensity from start to finish. Up until fairly recently, SIT was limited to competitive athletes and other highly fit individuals. However, there have been a number of SIT studies performed on the non-athletic ‘normal’ population in recent years showing that this method of training is very effective for improving cardiorespiratory fitness level and other health-related parameters.   

One such recent study from McMaster University in Canada has garnered much attention. A group of 25 sedentary men with an average age of 27 years participated in the study. At baseline, all men underwent a battery of tests including a measure of cardiorespiratory fitness via a maximal exercise test on a stationary bike. Additionally, several different indices of blood glucose and insulin levels, as well as a muscle biopsy of the quadriceps were performed. The men were then randomly assigned to one of three groups: sprint interval training (SIT), moderate intensity continuous training (MICT), or control (CON).  Both the SIT and MICT groups trained 3 days a week for 12 weeks, while the CON group remained sedentary throughout the study.

For the SIT sessions, subjects performed a 2 minute warm-up followed by 3 bouts of all-out maximal intensity cycling for 20 seconds. Each of these 3 bouts was separated by 2 minutes of low intensity cycling. Each SIT session was completed with a 3 minute cool-down period. The total time for each SIT session was 10 minutes.  For the MICT sessions, subjects performed a 2 minute warm up, 45 minutes of continuous cycling at approximately 70% of maximal heart rate, then a 3 minute cool-down. Thus, the total time for each MICT session was 50 minutes. A comparison of the SIT versus the MICT training sessions is shown in Figure 1 below.

All subjects underwent post-testing following the 12-week training period. The results were most impressive!  Both the SIT and MICT groups improved their cardiorespiratory fitness level by ~19%. Blood glucose and insulin parameters also improved significantly and to about the same degree in both the SIT and MICT groups. Muscle biopsy results showed significant similar beneficial changes in enzyme activity within the quadriceps in both the SIT and MICT groups. As expected, there were no changes in any variables within the CON group. So just to be clear, the SIT group experienced similar improvements when compared to the MICT group despite the fact that they spend 5-fold less time exercising (10 minutes per session versus 50 minutes per session)!

It is very important to note that this was not a weight loss study. No one is suggesting that 1 minute of SIT performed 3 times per week is an effective strategy for weight loss. The study focused on changes in cardiorespiratory fitness, blood glucose/insulin parameters, and skeletal muscle enzyme activity.  I would also like to emphasize that it takes a highly motivated individual to perform SIT and that such training is not suited for everyone!

Reference

Gillen, J. B., Martin, B. J., MacInnis, M. J., Skelly, L. E., Tarnopolsky, M. A., Gibala, M. J. (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.  PLOS One, 11(4): e0154075. doi:10. 1371/journal.pone.0154075

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