Exercise as it relates to Disease/The effect of exercise training on vascular function in type 2 diabetes

This piece aims to evaluate the 2001 study; ‘The effect of combined aerobic and resistance exercise training on vascular function in type 2 diabetes’.

Background to the Study
Type 2 diabetes is a progressive condition in which the body forms a resistance to the glycaemic control function of insulin. This condition is also characterised by the decreased or inability of the pancreas to produce sufficient insulin to meet the body’s needs. As a result, levels of blood glucose reach significantly higher readings than those considered within normal range. The progression of type 2 diabetes is strongly associated with lifestyle factors such as diet and physical activity levels.

Blood circulation is one of the numerous vascular functions crucial in maintaining the body’s homeostasis. Blood vessels are lined with an endothelium; a thin layer of simple squamous cells that form a protective barrier between the blood and surrounding tissue. Damage to this endothelial tissue leads to impaired vasodilation function and proinflammatory responses. Endothelial dysfunction is a contributing factor to morbidity in patients with type 2 diabetes. This study aims to determine whether participation in regular exercise has an effect on endothelium resistance or conduit vessel functioning.

Origin of Research
This study was conducted by a group of eight highly qualified academics from varying exercise science and cardiology institutions around Australia. The National Heart Foundation of Australia and the Medical Research Fund of Western Australia supported the study, which was finally published in the Journal of the American College of Cardiology in September of 2001. This journal is a highly reputable program and the leader in its field. Its member base reaches over 52,000 medical professionals and academics extending across all fields of medicine, and claims to be the ‘most read cardiovascular journal program worldwide’. The Journal of the American College of Cardiology publishes papers including peer-reviewed articles, clinical studies and editorials surrounding all aspects of cardiovascular health and disease.

Type of Research
This research study was a randomised control trial, indicating that participants were randomly selected to take part in a specific clinical intervention. Randomised control trials are qualitative measures of clinical trial outcomes derived from the comparison between a control group and a trial group. The concept of randomisation in this type of trial increases the accuracy of results by attempting to remove bias.

In this particular study, participants were randomly assigned to either a training or non-training program. The results from both groups were then compared to assess whether an exercise program affected various mechanisms involved in the participant’s vascular functioning.

What did the Research Involve?
The study involved sixteen participants with diagnosed type 2 diabetes, 14 male and 2 female. All participants were non-smokers with an average age of 52 years. There were no reports of any renal impairment, proteinuria, hepatic impairment, hyperuricemia, hypercholesterolemia or hypertension.

All participants in this study were taking various medications throughout the course of the eight-week program. The following medications were taken by one or more participants;
 * Angiotensin-converting enzyme inhibitor
 * Lipid-lowering therapy
 * Asprin
 * Oral hypoglycaemic

Participants were randomly assigned to an eight-week training or non-training program. Assessments were conducted at the start and conclusion of the eight-week period, as well as 16 weeks following the start date. High-resolution ultrasounds were used to assess conduit vessel endothelial function, and forearm plethysmography and intrabrachial infusions of acetylcholine and sodium nitroprusside were used as assessments of vessel resistance. Participants also completed a graded incremental VO2 max test to assess aerobic endurance.

The training program consisted of three 1-hour sessions per week. These sessions combined aspects of aerobic endurance and whole body resistance exercises, excluding those involving forearm strength. The seven resistance exercises used in this study were; dual seated leg press, left and right hip extension, pectoral exercises, shoulder extension, seated abdominal flexion and dual leg flexion.

Results
Results yielded from this study indicate that regular exercise provides several vascular benefits for patients with type 2 diabetes. Flow mediated dilation of the brachial artery was significantly increased in the exercise group, indicating that participation in both aerobic and resistance training assists in maintaining optimal endothelial functioning. Results also signify that the concentration of glycated haemoglobin was decreased in the exercise group. This suggests that participation in regular exercise leads to improvements in glycaemic control.

Conclusions of the Study
This study concludes that regular participation in aerobic and resistance-based exercise reduces endothelial dysfunction and therefore pathogenesis of vascular disease in individuals with type 2 diabetes. The coherent methodology and assessment techniques used in this study supports the reliability and validity of results. Although, many of the assessments including plasma volume, triglycerides and lipoprotein cholesterol levels reported no significant change with exercise. This suggests that further consideration when selecting appropriate assessments for this study would benefit by eliminating irrelevant data, and in turn decrease economic burden.

More recent research on the effects of exercise on vascular functioning in type 2 diabetes patients found similar adaptations in adolescent participants. Another study concluded that lower intensity exercise, in particular, promotes greater physiological improvements of endothelial function. Significant increases in brachial artery flow mediated dilation was reported, reflecting those found in the study under review. Interestingly, participants that were prescribed low to moderate intensity exercise generated greater flow mediated dilation following exercise to those prescribed to high intensity.

Practical Advice
Several limitations of this study inhibit its ability to reflect a broad population. One major limitation is the use of only sixteen participants with a significantly higher number of males. Increasing the sample size and creating greater gender variability would assist in ensuring these results are applicable to a larger population. In doing so, the validity and reliability of results would also be improved.

Another limitation is the large variability in medications used by participants. A total of four types of medication were reportedly taken by participants throughout the duration of this study. Some of these medications impacted results such as those exhibited in the differences of flow mediated dilation between patients taking lipid-lowering medication (2.9 ± 1.9%) and those not (3.3 ± 0.6%).

Further studies should be conducted to compare the effects of specific exercise types on different variables. An example of this would be analysing the difference in aerobic training versus resistance training in type 2 diabetes patients. This could be enhanced by also assessing and comparing the results of variables such as gender, different age groups, individuals prescribed to similar medications, weight categories and physical activity status. This data would be highly beneficial when developing specific and individualised training programs for type 2 diabetes patients in the future.

Further Information
Refer to the additional resources below to further enhance understanding of vascular functioning in type 2 diabetes, as well as the importance of exercise on glycaemic control.

Diabetes Australia - Type 2 Diabetes

Determinants of Vascular Function in Patients with Type 2 Diabetes

Effects of Different Modes of Exercise Training on Glucose Control and Risk Factors for Complications in Type 2 Diabetic Patients