# Exercise as it relates to Disease/High Intensity Interval Training: effect on Metabolic Syndrome factors
## Metabolic Syndrome: What is it?

Metabolic Syndrome is not a specific diseased state, but rather a cluster of conditions including central or visceral adiposity and dyslipidaemia, type II diabetes and insulin resistance, and cardiovascular disease and hypertension. Metabolic syndrome is defined by the International Diabetes Federation as central obesity as well as two of the following states: triglycerides greater than 150 mg/dL, HDL cholesterol levels lower than 40 mg/dL for males, 50 mg/dL for females, blood pressure greater than 130/85 or undertaking treatment for hypertension, and fasting plasma glucose levels greater than 100 mg/dL or type 2 diabetes. The consequences of metabolic syndrome are extensive, including the patient being five times more likely to develop diabetes, an increased risk of cancers partially due to elevated insulin (a growth factor) levels, the development of non-alcoholic fatty liver, and chronic inflammation. Here, exercise as a means to improve the factors comprising Metabolic Syndrome are discussed with regard to the somewhat controversial High Intensity Interval Training (HIIT) exercise method.

## HIIT evidence for Obesity, Dyslipidaemia and Chronic Inflammation

With increased adiposity comes an increase in inflammation due to pro-inflammatory cytokines stimulated by increased M1 macrophage levels, including those released from adipose tissue itself, such as interleukin 6 and c-reactive protein, a key marker of inflammation. To reduce the chronic inflammation associated with obesity, adiposity must be reduced. A number of studies have shown a significant increase in the body’s ability to oxidise fat resulting from HIIT interventions, even for as short a time as 2.5 hours over a 2 week period. These results all show similar or superior effects to continuous type training with regard to oxidative enzyme activity and mitochondrial capacity. Of interest, peroxisome-proliferator activated receptor γ coactivator PGC-1α levels significantly increase following low volume HIIT, which is associated with increased oxidative capacity and mitochondrial enzyme expression, and importantly, anti-inflammatory pathways, including the increase in circulating adiponectin.
Addressing dyslipidaemia, visceral fat stores are comparatively less ‘stable’ than others, tending to release excess free fatty acids, which is a contributing factor in the instance of dyslipidaemia. A reduction in visceral fat storage would therefore be desired to contribute to the reduction in severity of dyslipidaemia. In addition to the increased oxidative capacity observed with HIIT, a study conducted on metabolic syndrome patients revealed HIIT the superior training choice when compared to continuous training, with results including greater decreases in lipogenesis, fatty acid transport into adipose tissue, waist circumference and body weight, indicating a reduction in visceral fat storage and an increase in the body’s ability to metabolise fat with a HIIT exercise intervention.

## HIIT evidence for Type 2 Diabetes and Insulin Resistance

The increased mitochondrial enzyme activity discussed above, while increasing oxidative capacity and ability to oxidise fats, also benefits the metabolic syndrome patient with a reduction in the risk and severity of other metabolic disorders, including insulin resistance. HIIT in metabolic syndrome patients has been found most effective in the improvement of insulin sensitivity, fasting blood glucose and cell function when compared to continuous training. The earlier mentioned PGC-1α not only benefits muscle oxidative capacity and anti-inflammatory mechanisms, but also has a positive effect on glucose uptake.
HIIT has been found to increase skeletal muscle glucose transport capacity in patients with type 2 diabetes, through increased insulin sensitivity, and by the increased skeletal muscle content of the chemical mediator GLUT4. Following a HIIT program, subjects were also found to have a higher muscle glycogen content, a lower rate of glycogen utilisation, and an increased capacity for lipid oxidation after just 2 short weeks comprising six HIIT sessions.

## HIIT evidence for Cardiovascular Disease and Hypertension

Though often perceived as an inappropriate and unsafe form of training, interval based training techniques have provided numerous benefits in applications to a range of populations, including cardiovascular conditions such as coronary artery disease, hypertension and post-infarction heart failure. It is thought that short intense bursts of activity, while causing increases in peripheral vascular stress, may in fact ‘insulate’ the heart from such stresses due to the brief exercise duration. Compared to continuous training, HIIT has been found to have a greater flow on effect with the reduction of blood pressure, and increases in endothelial function, and of the two types of training, HIIT was the only one found to decrease arterial stiffness.
Aerobic capacity has been well documented to be superiorly developed using HIIT training when compared to continuous training, particularly on a time to results basis. An increase in cardiovascular fitness has been noted when applying HIIT techniques to coronary artery disease patients. Aerobic capacity determined by VO2 peak was found to increase significantly with HIIT when compared to continuous training (46% and 14% respectively) in a study of patients with stable post-infarction heart failure. Additional findings revealed declines in end-diastolic and end-systolic volumes, and increases in left ventricular ejection fraction brachial artery flow with HIIT, and quality of life.

## Recommendations

Previously regarded as an unsafe and inappropriate exercise tool for many populations, HIIT has gained much credit in the literature as a potentially beneficial mode of exercise for the improvement of a number of conditions, including those comprising Metabolic Syndrome. The exact volume, frequency and intensity is yet to be determined as HIIT focus is relatively new. Studies as short as 2 weeks with 3 sessions per week have proven HIIT benefits significantly superior to continuous training. However, as a general consensus, a HIIT exercise intervention of 10–16 weeks, involving 3 HIIT sessions per week, with achieved intensities of 80-95% peak HR during 2-4 minute high intensity periods and 40-70% peak HR during 2-3 minute active recovery periods, repeated 4-6 times provides sufficient training stimulus for positive adaptations in those presenting with Metabolic Syndrome factors. However, before undertaking any physical activity program, a medical exam must first be conducted to determine the appropriateness of a HIIT intervention, and to provide any individual limitations, for example, for diabetics with conditions such as retinopathies. Any program will be of most benefit when tailored to each individual, and additionally overseen by a physician. Where appropriate, a combination of exercise equipment involved in the provision of HIIT is ideal, as this provides total body training, stimulating the greatest amount of skeletal muscle tissue prospective of adaptation, as well as benefiting the patient with whole body exercises improving personal strength and range of motion, and follows cardiac rehabilitation procedures.

## Further reading

International Diabetes Federation's 'The IDF Consensus Worldwide Definition of the Metabolic Syndrome' (2006) provides valuable and clear information regarding the classification, diagnosis and management of Metabolic Syndrome.

## References

* 1 2 3 4 International Diabetes Federation. The IDF Consensus Worldwide Definition of the Metabolic Syndrome. Brussels, Belgium: International Diabetes Federation; 2006.
* ↑ Grundy SM. Metabolic Syndrome: connecting & reconciling cardiovascular and diabetes worlds. Journal of the American College of Cardiology. 2006;47(6):1093-1100.
* 1 2 3 Shoelson SE & Goldfine AB. Fanning the flames of obesity-induced inflammation. Nature Medicine. 2009;15(4):373-374.
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* 1 2 3 4 5 Talanian JL, Galloway SDR, Heigenhauser GJF, Bonen A & Spriet LL. Two Weeks of High-Intensity Aerobic Interval Training Increases the Capacity for Fat Oxidation During Exercise in Women. Journal of Applied Physiology. 2007;102:1439-1447.
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* 1 2 3 4 5 6 7 8 9 10 Tjonna AE, Lee SJ, Rognmo O, Stolen TO, Bye A, Haram PM, Loennechen JP, Al-Share QY, Skogvoll E, Slordahl SA, Kemi OJ, Najjar SM & Wisloff U. Aerobic Interval Training Versus Continuous Moderate Exercise as a Treatment for the Metabolic Syndrome. Circulation: Journal of the American Heart Association. 2008;118:346-354.
* 1 2 3 4 5 6 7 8 9 Wislof U, Stoylen A, Loennechen JP, Bruvold M, Rognmo O, Haram PM, Tjonna AE, Helgerud J, Slordahl SA, Lee SJ, Videm V, Bye A, Smith GL, Najjar SM, Ellingsen O & Skaerpe T. Superior Cardiovascular Effect of Aerobic Interval Training Versus Moderate Continuous Training in Heart Failure Patients: A Randomised Study. Circulation: Journal of the American Heart Association. 2007;115:3086-3094.
* 1 2 3 Little JP, Safdar A, Wilkin GP, Tarnopolsky MA & Gibala MJ. A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms. Journal of Physiology. 2010:1011-1022.
* ↑ Carr MC & Brunzell JD. Abdominal Obesity and Dyslipidemia in the Metabolic Syndrome: Importance of Type 2 Diabetes and Familial Combined Hyperlipidemia in Coronary Artery Disease Risk. Journal of Clinical Endocrinology & Metabolism. 2013;89(6):2601-2607.
* 1 2 3 4 5 6 Warburton DER, McKenzie DC, Haykowsky MJ, Taylor A, Shoemaker P, Ignaszewski AP & Chan SY. Effectiveness of High-Intensity Interval Training for the Rehabilitation of Patients with Coronary Artery Disease. The American Journal of Cardiology. 2005;95:1080-1084.
* 1 2 Guimarães GV, Ciolac EG, Carvalho VO, D’Avila VM, Bortolotto LA & Bocchi EA. Effects of Continuous vs. Interval Exercise Training on Blood Pressure and Arterial Stiffness in Treated Hypertension. Hypertension Research. 2010;33(6):627-632.
* 1 2 3 4 Rognmo O, Hetland E, Helgerud J, Hoff J & Slordahl SA. High intensity aerobic interval exercise is superior to moderate intensity exercise for increasing aerobic capacity in patients with coronary artery disease. European Journal of Cardiovascular Prevention and Rehabilitation. 2004;11:216-222.