Exercise as it relates to Disease/Effects of cycle training on metabolic syndrome

The following is a fact sheet regarding the impact of eight weeks of progressive cycle training on insulin resistance in metabolic syndrome. A 2014 study titled ‘Insulin Responsiveness in Metabolic Syndrome after Eight Weeks of Cycle Training’ by Stuart. C et al is critiqued and insights are offered into the research and its practical implications.

1. Background to the Research

Obesity and diabetes have an increasing prevalence in western society in recent years, particularly in Australia and the United States. Insulin resistance, hyperinsulemia, visceral obesity, hypertension and dyslipidaemia are all components of the pre-diabetic state known as metabolic syndrome. Reaching exercise guidelines is beneficial in the prevention and management of type two diabetes and metabolic syndrome. A similar 2012 study by Grontved et al. suggested that sufficient combination of aerobic and resistance training can lower the incidence and reverse the effects of type two diabetes in men.

2. Where is the research from?

The research was conducted at the East Tennessee State University by Charles A. Stuart, Mark A. South, Michelle L. Lee, Melanie P. McCurry, Mary E. Howell, Michael W. Ramsey, and Michael H. Stone and was published in November 2014.

3. What kind of research was this?

The research at hand is an experimental case-control study. The subjects were divided into two groups to investigate the differences in results from the training intervention. All subjects were still classified as ‘sedentary’: - Those classified to have metabolic syndrome (high risk for type two diabetes n=11) - The control group (low risk for type two diabetes n=7)

4. Research Methodology

The study involved 8 weeks of stationary cycle training 4 times weekly in conjunction with mid-section resistance training which was performed once a week. 18 sedentary subjects were recruited that had reported to not have engaged in regular physical activity for the past year. The subjects were classed into two groups; high risk for diabetes (BMI>30 and family history of diabetes) and low risk for diabetes (BMI <30 and no family history of diabetes). The 11 subjects in the high risk group qualified to have metabolic syndrome as set by the International Diabetes Federation. Subjects performed four five minute sets of cycling at a specific resistance with 1 minute light cycling between sets. The cadence was 75-85 rpm and the intensity began at 100 watts and increased weekly. Three day dietary reviews were undertaken and analysed to ensure that body composition remained relatively unchanged and was also monitored throughout the study. The content of insulin receptor subunits IRS-1, Glut 4 and STP synthase were assessed through immunoblotting before and after the training intervention. Muscle Fibre type, composition and size were also quantified through muscle biopsy of the vastus lateralis and image analysis software. Euglycemic clamp was used to reach an insulin concentration of 50 μU/mL. 90 minutes after the infusion steady state glucose infusion rate was used to quantify insulin sensitivity.

5. Basic Results

There were some changes to insulin resistance when measured by assessing B cell function and indexing insulin sensitivity. The control group improved responsiveness somewhat compared to the metabolic syndrome group although these changes were not seen to be statistically significant. The mean steady state glucose infusion rate remained unchanged in both the metabolic syndrome and control groups at the conclusion of the 8 weeks of cycle training, indicating that insulin resistance was unaffected. Three mechanisms of the insulin signalling pathway were quantified before and after the intervention. The expression of insulin receptors, insulin like receptor substrate 1 and GLUT4 were recorded through muscle biopsy. Insulin receptor expression showed an overall increase in both groups post training, Glut 4 was slightly increased in the metabolic syndrome group however, expression of IRS-1 decreased. Despite the fact that insulin sensitivity did not improve after the stationary cycle training intervention increases in some of the signalling pathway elements were improved. Although slight, the changes in these mechanisms could have the potential to improve insulin resistance in type two diabetics and metabolic syndrome.

6. Researcher’s Interpretation of the Results

Due to the results of the study researchers have concluded that the cycle training intervention alone is not sufficient to have significant effects on insulin resistance in both those classified to have metabolic syndrome and controls. It was concluded that although there were some health benefits to the subjects as a result of the aerobic exercise intervention, without a change in diet or body composition the impacts on insulin sensitivity were minimal.

7. What conclusions should be taken away from this research?

The primary conclusion taken from the study is that without change in body composition, aerobic exercise does little to increase insulin sensitivity. A study by Davidson et al. looked at the effects of different training methods in enhancing insulin sensitivity. The same steady state glucose infusion rate was used to measure insulin sensitivity and it was found to respond best to the group that combines both aerobic and resistance training. A 2014 study by Bouchonville et al supports the claims made in the study by Stuart et al. and further investigates claims made by Davidson et al. The study investigated the effects of weight loss from diet, exercise without weight loss, and exercise with weight loss (decreasing fat mass). The exercise prescribed was a combination of both aerobic and strength training and insulin sensitivity was tested by an oral glucose tolerance test. Insulin sensitivity index improved in both the weight loss and weight loss with exercise group with the greatest improvements found in this group. The control and exercise only group showed no change in insulin sensitivity, supporting the findings in the study by Stuart et al.

8. Implications of the Research

The research has great relevance for the community given the rise of diabetes and obesity in western society in recent years. The research has highlighted the best methods to reduce insulin resistance, the key factor in metabolic syndrome and type two diabetes. The results of this research provides insight into how to reduce the growing problem of insulin resistance in type 2 diabetes and the associated strain on the healthcare system. It should be noted that the study being critiqued did have a relatively low number of subjects participating (n=18). This is not a high enough number of participants to draw definite conclusions from the results presented. However, the article does make reference to a number of other studies which yield results that support those of the study. These studies have much higher sample sizes and thus, may yield more reliable results.

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