Exercise as it relates to Disease/Is high-intensity interval exercise preferential for people with type 2 diabetes?

This is a critique of the research article:

What is the background to this research?
Lack of time to exercise is a very commonly used reason for a lack of exercise amongst the general population, and people with type 2 diabetes have lower levels of PA than the general population. Since exercise is the first line of defence and a highly effective treatment option for type 2 diabetes mellitus (T2DM), it is critical that tactics are adopted which can increase PA levels over the long term.

T2DM is a loss of the bodies ability to appropriately secrete insulin whilst increasing the bodies insulin resistance. This results in an inability of the body to remove glucose from the bloodstream, a necessary process for continued cell function. Exercise is effective at managing this condition as it both promotes increased production of insulin and allows glucose to enter the cells of the body utilising different pathways than have become resistant.

High Intensity Interval Exercise (HIIE) is a style of exercise which promotes short bursts of intense exercise, followed by longer periods of much lower intensity to recover. Because of the much higher intensity of the working periods this style of exercise allows one to burn an equivalent amount of energy in a much shorter period of time than traditional Moderate Intensity Continuous Exercise (MICE).

Where is the research from?
This research was conducted at a single center in Brazil. Participants were gathered from the city of Bauru. Calls for participants were left in social areas, public transport hubs and local health centers.

What kind of research was this?
this study was a randomised crossover intervention. There were four different interventions which each participant undertook in a random order. The four interventions were a Control (CON), MICE, HIIE using heartrate (HR) to measure output and HIIE using (RPE) to measure output.

Participants were standardised in that they all had T2DM. They had to be physically inactive, meaning no regular physical activity or exercise program for at least a 6-month period before the study. They required unchanged drug therapies for the previous 3 months and were required to be free from long term diabetic complications. Full participation in the study from beginning to end of the interventions was required to be included in the final study. Of all the potential participants, only 11 met these exclusion criteria, 2 men and 9 women.

What did the research involve?
Before any interventions were completed, participants were referred for (CPX). This testing was used to regulate the participants HR in the HIIE HR intervention. Participants undertook all of the interventions in a random order, determined through a draw. There was 2 – 5 days between completion of each intervention and all interventions were completed at the same time of day. Attempts were made to standardise consumption from the participants. Everyone was asked to only have a light meal within 2 hours of their intervention and to not consume caffeine or alcohol within 24 hours of their intervention. They were instructed to continue any medication they were using and to consume similar breakfasts and lunches on the day of each intervention.

Several measures were taken pre, post, and 45 minutes after each intervention. These measures were Blood Pressure (BP), Heart Rate, blood glucose levels (BG), Pulse wave velocity, and endothelial reactivity. HR was also monitored continuously during each intervention and a 24 hour was monitored after each.

The interventions were all completed in a climate controlled environment, 3 – 7 days after CPX, and 2 – 5 days between interventions. The interventions were as folows:


 * HIIE HR completed a 4 minute walking warm up (50% HR reserve), 21 minute of HIIE alternating 1 minute jogging/running (85% HR reserve) and 2 minutes walking (50% HR Reserve)
 * HIIE RPE completed a 4 minute walking warm up (RPE 9), 21 minute of HIIE alternating 1 minute jogging/running (15-17 RPE) and 2 minutes walking (9-11 RPE)
 * MICE completed a 4 minute walking warm up (RPE 9), 26 minute of walking/running (11 – 14 RPE).
 * CON was 30 minutes of resting quietly in a sitting position.

The speed and distance was blocked from the view of the participant. HIIE HR speed was controlled by an exercise specialist based upon the participants HR response. Whereas HIIE RPE and MICE speed was regulated entirely by the participant and their determined RPE.

What were the basic results?
Not surprisingly, HR and speed were significantly different in both HIIE interventions when compared to MICE. However there was no significant difference between mean HR and speed, exercise distance, and estimated energy expenditure between the interventions.

there were similar values in BG following both HIIE interventions which were significantly different to MICE. The HIIE interventions lowered BG more so than did the MICE intervention. This is in line with several other studies of HIIE and is explained through the increased use of carbohydrate as an energy source as intensity increases and also through the increased muscle activation during HIIE.

only HIIE RPE showed a significant difference between 24 hour systolic blood pressure values.

What conclusions can we take from this research?
This study is a proof of concept about the acute benefits of HIIE in comparison to MICE. These results show that the benefits of HIIE are equivalent to MICE with a shorter time commitment. In the case of acute glycaemic control HIIE was superior to MICE.

The results also indicate that RPE can be used effectively to moderate exercise intensity without the need of constant monitoring of HR or an exercise specialist involved. This can be done without sacrificing the potential benefits of HIIE on T2DM.

Practical advice
This study was by no means free of limitations, which affect what practical advice can be given to people with T2DM. a relatively low sample size, and that each participant only completed an intervention once, means there is no certainty if the results would be the same in everyone. Because the study only looked at the immediate effects of the interventions, no conclusions can be drawn about the long term effects of the different training modalities. The study did not measure BG in the 24 hours after interventions, as it did with BP. As such, we don't know whether BG remained low, or returned to pre-intervention levels. In some cases BG may increase beyond initial levels due to the increased catecholamine activity, which has been shown to increase after HIIE.

That being said, this study gives support that people with T2DM, who complain of lack of time, can be recommended HIIE to receive similar beneficial results as current recommendations, for less of a time commitment.

This study gives evidence through the use of RPE at moderating intensity of exercise, that participation in group fitness classes or other alternatives is safe and effective for T2DM. This will increase exercise availability to people of lower socioeconomic status, who are more at risk of developing T2DM, as they do not need a personal trainer or expensive HR monitoring equipment.

Further resources

 * Place to learn everything you need to know about diabetes in Australia.
 * A government initiative specifically to help people manage living with their diabetes.
 * Non-government organisations in Australia which provide information and events for members.
 * https://diabetessociety.com.au/
 * https://www.adea.com.au/