Exercise as it relates to Disease/High intensity exercise in diabetic population

The following Wikibooks page is a an analysis of the journal article "Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes" By Little et al (2011).

High Intensity Interval Training

High intensity interval training or HIIT is performed not by running the furthest distance or for the longest duration. But by performing the exercise with maximum intensity for the duration of the defined interval, this is defined by an individual's feeling of effort or exertion while doing an exercise. HIIT is has already been shown as a time efficient method for improving health, the validity of HIIT has already been shown in improving the condition of patients with heart failure, obstructive pulmonary disease and as well as metabolic syndrome.

Positives

HIIT is the preferred means of exercise over regular aerobic exercise such as a 45 minute jog for many reasons.

• This training method elicits the EPOC (Excess Post Exercise Oxygen Consumption) process which increases the consumption of oxygen after a training session
• HIIT training when compared with regular duration based exercise of the same type can have the same metabolic effect in at least half and in some cases a quarter of the time
• With jogging the metabolic rate is raised during the duration of the exercise, whereas with HIIT sprints the metabolic rate remains raised for up to 48 hours post exercise, this has important implications for those with metabolic conditions such as diabetes
• In a study carried out by Tabata, after 8 weeks of HIIT, the participants anaerobic capacity increased by 28% while the VO2 max results were improved upon by 14%

Negatives

This training method may also not be ideal for all populations for a few different reasons.

• HIIT is literally highly intensive and while this is relative to the rating of perceived exertion (RPE) of the individual, elderly and obese populations are not as likely to be suited to this method
• It may not also be suited to those that are sedentary and progressing back to activity, HIIT requires a lot of the body and can rapidly alter both heart rate and blood pressure, such fluctuations are not seen in sedentary populations
• Over-training is much more likely

HIIT Considerations

With a few positive and negatives of this method of training stated, it is important to remember a few key points when undertaking HIIT.

• Train until failure to stimulate new growth
• Good nutrition as important as good intensity throughout a training regime
• Each exercise should be preformed with good quality and consistency, use of momentum or break of form should be considered failure

Current Study

What Is The Background To This Research?

This research relates to patients with type 2 diabetes (T2D). T2D is a metabolic condition where the glucose levels in the blood are too high, this type of diabetes affects around 90 percent of all people with diabetes. Insulin is a hormone made by beta cells in the pancreas and is responsible for opening the channels that allows glucose in the blood to be transported into body cells. Type 2 differs from Type 1 diabetes (T1D) as those affected by T1D cannot produce insulin while those with T2D suffer from insulin resistance and not enough in produced as is needed, this lack of insulin means less get into the cells and more is left in the bloodstream, this often leads to complications.

Based on this understanding of T2D and the knowledge of the metabolic effects of HIIT post exercise when compared to regular and traditional aerobic exercise, it is thought that HIIT must have some qualitative effects on the glucose and insulin activity in type 2 diabetics. The researchers stated that, "Most studies examining the therapeutic effects of exercise in T2D involvecontinuous, low to moderate intensity exercise such as walking, jogging, or cycling for a sustained 30 minutes although the optimal strategy has not been established, higher intensity exercise may be more effective for improving glycemic control in patients with T2D"

Where Is The Research From?

This study was undertaken by researchers from the department of Kinesiology, Pediatrics and Medicine at McMaster University, Ontario and researchers at the School of Health and Exercises at the University of British Columbia. The Canadian Diabetes Association and the Natural Sciences and Engineering Council (NSERC) of Canada provided the funding for this study, and provided the glucose monitors and sensors.

What Kind Of Research Was It?

The study carried out was a controlled clinical trial with a clear experimental design. The aim was to view the effect of low volume HIIT on hyperglycemia as well as muscle mitochondrial capacity in patients with type 2 diabetes. The recommendation is for 150 minutes of moderate to vigorous exercise a week. While this study only had patients performing 30 minutes total of high intensity exercise in a week.

What Did The Research Involve?

Participants

Participants were selected through diabetes clinics, they were diagnosed more than three months prior and to the standard criteria of a fasting and oral glucose test with no other uncontrollable risk factors. Of the eight participants selected, six self reported as sedentary with less than 30 minutes of exercise a week, while the two other participants reported above 30 minutes of exercise a week. From the eight participants six were currently taking blood glucose lowering medications. The participants were also told to not change their regular activity or dietary habits mainly due to the short nature of the intervention being only two weeks.

Experimental Design

The experiment consists of four stages that will be explained

Medical Clearance and Familiarisation

To begin the test all participants were required to undergo a maximal test with a pre and post 12-lead electrocardiogram (ECG) to make sure that there were in fact no health conditions that could be worsened by the study. This screening test started at 30 W on the cycle ergometer and increased by 15 W a minute until exhaustion or the signal to stop. W max and maximal heart rate were recorded. Following being cleared on the ECG by a physician, two familiarisation tests occurred. This also served as a way to calibrate the test to elicit around the 90% mark of heart rate max by finding the appropriate interval time and power change.

Baseline Testing

After clearance participants performed a 15 minute sub maximal walking test to examine the cardiovascular response (heart rate) and RPE, RPE was measured using the 0-10 continuous scale.

Two days after, constant glucose monitoring devices (CGM) were inserted and participants were given a glucose meter with instructions, as well as a control diet for each individual. Two days later the CGM was removed and a resting skeletal muscle biopsy sample from the vastus lateralis.

Training

Five days after the biopsy, the participants began training. The training involved three sessions a week (Monday, Wednesday and Friday) for the duration of two weeks, equaling six sessions in total. Each training included a 3 minute warm up at 50 W, each individual workload was tailored from the baseline testing, but all were required to perform 10 x 60 second cycling intervals. These intervals were intersected with 60 seconds of recovery where the participants could decide to rest or pedal at a resistance of 50 W. In total the training session would take 25 minutes, adding up to a 75 minute total time requirement a week.

Post testing

After the training period of two weeks, CGM data was recorded again 48 hours after the final training session and the diet was controlled to be the same as pre training for each participant. 72 hours preceding the final session, muscle biopsy samples were taken again. An additional 72 hours after the biopsy the walk test and maximal exercise test were performed as they were in the pretesting. Finally the perceived enjoyment of low volume HIIT was assessed by simply asking participants using the point likert scale ranging from 1 to 9. The questions asked were, how enjoyable would they find:

• A single bout of 10 x 1 minute HIT
• HIIT three times a week for the next four weeks

Results

Continuous Glucose Monitoring

Two weeks of HIIT improves glycermic control. Pre and post training values across all participants followed a similar trend with the average blood glucose concentration over the 24 hour testing period .

• Pre-test result: 7.6 mmol/l
• Post-test result: 6.6 mmol/l

While the results postprandial (the sum of the three hours after a meal) was significantly lower, validating the HIIT research that suggests HIIT increases EPOC and raises the metabolic rate 48 hours after exercise.

• Pre-test result: 965 mmol/l−1·9 h−1
• Post-test result: 679 mmol/l−1·9 h−1

Adaptations in Skeletal Muscle

The activity of citrate synthase (CS) measured in skeletal muscle biopsy samples elevated following the training period when compared to the pretesting results.

• Pre-test CS: 2.7mmol/kg/hr
• Post-test CS: 3.5mmol·kg/hr

Another interesting result was the significant increase in the GLUT4 concentration in pre and post with this insulin regulated protein almost quadrupling in concentration.

• Pre-test GLUT4: 1 a.u.
• Post-test GLUT4: 3.9 a.u.

Functional Exercise Performance

The maximal workload on the maximal test increased from pre to post test, reinforcing the findings of adaptations in skeletal muscle.

• Pre-test W: 111 W
• Post-test W: 124 W

Training reduced heart rate as well as RPE during the walk test.

• Pre-test HR and RPE: 73 and 2.4
• Post-test HR and RPE: 66 and 1.3

Conclusions

It is clear from the results of this study that even two weeks of low volume HIIT, involving as little as 30 minutes of intensive exercise can not only reduce average blood glucose concentration but can also reduce post meal blood glucose rises significantly. This may be due to the also increased markers in the skeletal muscle of mitochondrial activity and capacity seen by the rise in GLUT4 protein. This protein allows for proper muscle glucose uptake which can have a huge impact on glycaemic regulation. Overall it is apparent that HIIT can reduce the resistance to insulin in the body. All this is achieved in a 75 minute a week commitment which is half what is the current guidelines that expect at least 150 minutes. It is clear from this study that while more long term and broader (more participant) studies are required for a definitive result on the effects of HIIT on T2D, it is clear from these results that replication of these positive results is to be expected.

Practical Advice

By doing as little as three 10 minute HIIT sessions a week, populations with T2D will see a positive health improvement. This improvement is in a drop in insulin resistance through the increase of the GLUT4 proteins in the muscles as well as better glycaemic regulation. It is important to remember the medical clearance of this study as well as the walk and maximum pre testing. While you may feel like you are able to perform these exercises it is recommended you speak with a medical professional or your diabetes care team for a referral or recommendation on appropriate exercises for you and your specific condition as not all T2D are identical and not all people are identical. While this study recommends HIIT it is also considered that not all populations may be capable of HIIT and proper testing is advised before attempting vigorous HIIT.

Further Information

More basic information on diabetes.

Diabetes overview https://www.diabetesaustralia.com.au/what-is-diabetes

Cause of diabetes https://www.niddk.nih.gov/health-information/diabetes/overview/symptoms-causes

Living with diabetes https://www.diabetesaustralia.com.au/managing-type-2

Exercise and diabetes https://www.endocrineweb.com/conditions/type-2-diabetes/type-2-diabetes-exercise

Study used in this review http://m.jap.physiology.org/content/111/6/1554.full