Introduction

As you can see from our Background Information page obesity is a growing epidemic. Traditional Endurance Training reduces the risk of obesity and other diseases associated with it like cardiovascular disease, however, it requires a large time commitment and finding time to do it every day might prove difficult. High Intensity Interval Training is basically combining Endurance Training and Resistance Training without a large time commitment.

With High-intensity interval training (HIIT) you get all the benefits of traditional endurance exercise ¹ without having to go on a long run every day. A common way of doing HIIT is on a Wingate bike which allows you to increase the resistance on its wheel by adding weight to it. When this weight is added to the wheel you do a 30s-1min ² sprint on the bike and then take 4 minutes of rest, you repeat the sprint five more times in that session taking a 4 minute break between each sprint.

Meta-Analysis

The overall effect on BMI was not significantly different between HIIT and traditional exercise ¹. The reason for no significant change in BMI could be that the weight loss in fat mass was gained back in muscle mass, however, the muscle mass was not taken into consideration in this study, but you would expect an increase in muscle mass during HIIT. However, there was a significant reduction in % body fat when HIIT was compared to traditional exercise ¹, a decrease in % body fat is much more important to us than an increase in muscle mass. So, the fact that this meta-analysis saw a significantly greater reduction (p=0.02) ¹ in % body fat when compared to traditional exercise, is a very good thing.

Figure 1. Shows a forest plot of comparison: HIIT vs. Traditional exercise and their effect on %body fat ¹.

As you can see in figure 1 10 different studies have been compared, we are only going to look at the highlighted sections. The sections I have highlighted show the HIIT mean, the Traditional exercise mean and the difference between them. For most of the studies the mean difference favours HIIT, for Arad et. al. 2015, Lunt et. al. 2013 and Nicklas et. al. 2009 there is no difference in the means which isn’t a bad thing. However, Cocks et. al. 2015 shows a mean difference in favour of traditional exercise. What Cocks et. al. found was that % body fat was significantly reduced (p<0.05) in moderate-intensity continuous training (MICT) whereas the reduction was insignificant in their sprint interval training (SIT) group (p=0.235) ³, however they did only have n=8 people in each group so the results might not be reliable.

This forest plot shows whether the mean difference favours HIIT or Traditional exercise the green squares show the mean difference for each (of the 10) studies and the lines either side show the 95% confidence interval. However, the black diamond at the bottom is what really matters as this tells you if the studies Favour HIIT, traditional exercise or neither (only if it’s touching the 0 line).

You might now be thinking why everyone doesn’t do HIIT if it such a good way to lose weight in only a short 14-week ² intervention, well this will be covered in the next paragraph.

Downsides

Although HIIT is a good way to burn unwanted body fat, like all exercise it has its downsides even though it isn’t time consuming someone who is obese might struggle to find the motivation to do it every day. This is because even though it’s only for 30 seconds the sprint is tough, and can make you feel ill for a short time afterwards while your body catches up.

The intention of this paragraph isn’t to stop obese people trying HIIT as an alternative to endurance or resistance training, it is simply to make people aware of the difficulties involved in losing weight via HIIT.

Why HIIT is worth the trouble

You should stick with HIIT because it isn’t only going to help reduce your % body fat it has also been proven to improve insulin action in the body ⁴. I bring this up because we know that being obese puts you at an increased risk of type 2 Diabetes Mellitus and with type 2 DM your pancreas B cells don’t produce enough insulin, so if HIIT can reduce % body fat and improve insulin action it’s hitting two birds with one stone.

Figure 2a ⁴. Shows OGTT results of subjects before and after a 2 week HIIT intervention.

 

Figure 2b ⁴. Shows Plasma [insulin] in response to glucose before and after a 2 week HIIT intervention.

As you can see in figure 2b the [insulin] doesn’t increase as much in response to glucose after the HIIT intervention, however despite the decreased [insulin], Figure 2a shows that the plasma [glucose] stays constant from 0-60 mins and then after 60 mins it starts to decrease. What figures 2a and b are showing us is that the B cells don’t have to produce as much insulin to deal with the increase in [glucose] which suggests the insulin has become more effective at its job.

Conclusion

In conclusion, High-Intensity Interval Training is a very effective of losing body fat, however losing body fat isn’t all HIIT is good for. HIIT has also been seen to increase insulin action (figure 2b) in type 2 diabetics, so because obese people are at increased risk of Type 2 Diabetes Mellitus HIIT will not only decrease % body fat it will also reduce the risk of them getting Type 2 Diabetes Mellitus by increasing insulin action.

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References

1. Türk, et. al. High-intensity training in obesity: a meta-analysis. 2017.
2. Arad AD, et al. High-intensity interval training without weight loss improves exercise but not basal or insulin-induced metabolism in overweight/obese African American women. 2015.
3. Cocks M, et al. “Sprint interval and moderate-intensity continuous training have equal benefits on aerobic capacity, insulin sensitivity, muscle capillarisation and endothelial eNOS/NAD(P)Hoxidase protein ratio in obese men” Journal of physiology 594,8 (2015): 2307-21
4. Babraj J, al. Extremely short duration high-intensity interval training substantially improves insulin action in young healthy males. 2009 Jan 28;9(3).