Exercise as it relates to Disease/High-intensity interval training as an intervention for individuals with metabolic syndrome

This page aims to critically review the journal article The effect of different volumes of high-intensity interval training on proinsulin in participants with the metabolic syndrome: a randomised trial written by Ramos, J.S; Dalleck, L.C; Borrani, F; Mallard, A.R; Clark, B; Keating, S.E; Fassett, R.G; Coombes, J.S. Diabetologia. 2016. 59: 2308-20.

What is the background of this research?
Metabolic syndrome is a chronic disease that is caused by co-morbidities such as type 2 diabetes, central obesity, hyperlipidemia, and hypertension. It is estimated that 25% of the global population suffers from metabolic syndrome and the complex chronic diseases associated with it. While it is heavily researched due to the increasing prevalence rates worldwide, metabolic syndrome is not specifically curable and as such symptom management is important for the individual's quality of life.

One way to manage the symptoms of metabolic syndrome is physical activity. Exercise has been shown to improve insulin regulation, cholesterol management and blood pressure reduction as it targets various physiological processes in the body.

High intensity interval training (HIIT) is an exercise style that involves short bouts of high intensity exercise. This article explores the effect of HIIT on proinsulin, a marker for insulin resistance. One universally accepted characteristic of metabolic syndrome is insulin resistance, therefore, the article suggests a treatment for this specific symptom of metabolic syndrome sufferers. The study aims to develop further knowledge on evidence-based exercise prescription for sufferers of metabolic syndrome, as previous research focuses on drug therapy and dietary treatment in management of the disease.

Where is the research from?
The study was completed at the University of Queensland, St Lucia campus in Australia. The lead researcher of the study, Professor Jeff Coombes, is a professor in the human movement and nutrition department of the University of Queensland and has contributed to the ESSA student manual for health, exercise and sport assessment, as well as other studies researching the effects of HIIT on individuals with metabolic syndrome.

The journal in which the study was published, Diabetologia, is a peer-reviewed medical journal.

As such, there is low risk for bias due to the highly regarded researchers who worked on the article, and it's acceptance into a well renowned, peer-reviewed journal.

What kind of research was this?
The article describes a randomised control trial (RCT) with three exercise interventions: moderate-intensity continuous training (MICT), and two levels of HIIT, one that trained for 38 minutes 3 times a week (4HIIT), and one that trained for 17 minutes 3 times a week (1HIIT).

While RCTs are often considered reliable research methods, as the causation of the results are numerically stated in the paper. In this study, the control group was the MICT group as it reflects previously accepted evidence-based exercise prescription for sufferers of metabolic syndrome.

What did the research involve?
The study involved 99 participants who were diagnosed with metabolic syndrome according to the International Diabetes Federation. The group contained a mixture of individuals with and without type 2 diabetes.

The participants were assessed at a baseline level on cardiorespiratory fitness, through indirect calorimetry, body composition, through a dual-energy x-ray absorptiometry and 3 day food diary, and an oral glucose tolerance test.

The exercise intervention was completed 5 times a week in the MICT group and 3 times a week in the HIIT groups. The total intervention continued for 16 weeks after which participants reperformed the initial assessments.

Results
These results focus on a marker of insulin resistance (intact proinsulin) and cardiorespiratory fitness (absolute VO2 peak). The results have been divided by exercise intervention and the presence of type 2 diabetes in participants.

After the 16-week intervention, the 4HIIT group had the largest change in intact proinsulin, and the non-T2D group in the 4HIIT intervention was the only group to have a significant decrease in intact proinsulin, and therefore improvement in insulin resistance.

In terms of cardiorespiratory fitness, both HIIT groups showed change in absolute VO2 peak, however this change was not significant.

Critique
As the participants were from a clinical population, they were diagnosed with metabolic syndrome, they continued taking a variety of medications throughout the intervention, individual to each participant depending on the symptoms of their diagnosis. This has the potential to alter the results of the study, particularly those who were taking metformin for type 2 diabetes which has been known to alter the effect of exercise on insulin sensitivity.

Another critique is the length of the intervention. Whilst 16-weeks would be enough time to see changes in a healthy population, previous research has found a minimum of 9 months is required to see changes in type 2 diabetics in exercise interventions. As type 2 diabetes is a common symptom of metabolic syndrome, it is an oversight that the researchers did not consider the additional time required to see a result.

What conclusions can we take from this research?
Overall, HIIT for 38 minutes a day, 3 times a week has been shown in this study to improve insulin resistance in non-type 2 diabetics diagnosed with metabolic syndrome. This combined with the additional time required to see changes in type 2 diabetics, mean that replicating this study for specifically type 2 diabetics with metabolic syndrome over a period longer than 16-weeks could be beneficial to see significant change in insulin resistance.

Additionally, continuing the 4HIIT intervention would see further benefits of the exercise, not only as a potential for further change in insulin resistance, but also for general cardiovascular health in terms of VO2, as is seen in studying the effect of HIIT in healthy individuals.

However, it is important to consider the typical characteristics of populations with metabolic syndrome. One of the universally unifying factors in the definition of metabolic syndrome is the presence of central obesity. As such it is important to consider realistic compliance outside the research for ongoing health benefits.

Practical advice

 * For individuals with metabolic syndrome, and are not type 2 diabetic, it is worth participating in HIIT training for 38 minutes a session 3 times a week to continue preventing the development of type 2 diabetes, the 4HIIT condition.
 * For all individuals, those with and without metabolic syndrome, HIIT has been shown to have positive effects on the symptoms of metabolic syndrome.
 * Furthermore, using HIIT training can be used to treat pre-diagnostic conditions associated with metabolic syndrome.

Further information/resources
Below are further resources about metabolic syndrome and the accompanying symptoms. If you are concerned about your health, please speak to your GP.


 * Australian metabolic syndrome information
 * International Diabetes Federation
 * Seeing an Australian exercise physiologist- for any questions regarding exercise programming and training with a clinical condition such as metabolic syndrome
 * Diabetologia