Exercise as it relates to Disease/Sprinting and Obesity... Can it work?"
A critical appraisal of the journal article: "Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men" (Whyte LJ, Gill JM, Cathcart AJ. Metabolism. 2010;59(10):1421–8).
What is the background to this research?
Despite generally accepted knowledge that participating in regular physical activity lowers the risk of many diseases, participation still remains low. For many years The American College of Sports Medicine has stipulated that to attain the health benefits of physical activity, adults should aim to accumulate at least 30 minutes of moderate intensity exercise on most days. This recommendation is a common guideline for physical activity and is also implemented by the United Kingdom  and Australia.
Despite only being advised to accumulate 30 minutes of physical activity each day, lack of time has been reported as a significant barrier to exercise  and associated with low physical activity. If time is a major issue in physical activity participation, could a quick high intensity workout be the solution? Most recently The American College of Sports Medicine has placed greater emphasis on shorter duration, high-intensity exercise performed a minimum of 3 times per week.
This study aimed to investigate the effects of high-intensity sprint training on metabolic and vascular risk factors in overweight/obese sedentary men. If this type of exercise is proven to provide a meaningful and significant health benefit then perhaps guidelines might consider modifying their recommendations to include specific information on interval style training.
Where is the research from?
This research was conducted by Laura Whyte, Jason Gill and Andrew Cathcart from the University of Glasgow. The study was published in the journal: Metabolism Clinical and Experimental volume 59 in 2010. The Journal of Metabolism publishes original cutting-edge research papers exclusively in the field of metabolism related sciences.
All authors of this study have written a variety of papers centered around exercise performance and the relationship between exercise and health. Since publishing this 2010 study, Whyte and Gill have continued to research the the effect of high-intensity exercise on metabolic health biomarkers in overweight/obese sedentary men in their 2013 paper.
What kind of research was this?
This research is classified as an interventional study, specifically a single arm pre-post study due to only having one test group. There was no blinding in the study as all subjects were aware of the intervention and its aims. This study could have benefitted from a control group and perhaps other groups performing different exercise programs for comparison.
What did the research involve?
The participants in this study consisted of ten male volunteers between the ages of 18 and 40 who were overweight/obese and participated in less than 1 hour per week of structured exercise. The training protocol consisted of 6 sessions of sprint interval training across a 2 week period, with 1 to 2 days recovery in between sessions. Each session required the participant to perform 30 second "all out" sprints on a cycle ergometer with a fixed recovery period of 4.5 minutes.
A limitation of this study is the sample size, 10 subjects is not well representative of the entire population and may bias the results as outlying results can have a skewing affect on the mean and standard deviation. The other major limitation is that although subjects were asked to consume their normal diet and continue living their normal sedentary lifestyle, it is not guaranteed that they followed instructions. Without monitoring of diet and exercise one cannot say confidently that the sprint interval intervention was solely responsible for the health benefits experienced post study.
What were the basic results?
The researchers tracked many different health and physical fitness related measures at baseline and at 24 hours and 72 hours post-intervention in order to establish the physiological affects of this intervention. The crucial and most significant changes seen in the subjects after the intervention were:
- Increase in absolute (8.4%) and relative (9.5%) VO2 max. Higher aerobic fitness levels are associated with numerous health benefits most importantly a longer lifespan.
- Decrease in body mass (1.1%). Mortality rates decrease when a person's body mass index is within a healthy range.
- Decrease in waist (1.1%) and hip circumference (1.0%). Hip and waist circumference are a measure of abdominal obesity which is associated with increased risk of morbidity and mortality.
- Increased insulin sensitivity (23.3%). Low insulin sensitivity will stimulate the body to try to compensate by producing more insulin which can lead to health complications.
- Decreased fasting insulin (24.6%). Having a high level of circulating insulin (hyperinsulinemia) can lead to damaged blood vessels, high blood pressure, heart disease, heart failure and obesity.
- Decrease in systolic (5%) and diastolic (12.7%) blood pressure. High blood pressure or hypertension, can increase the risk of stroke, heart attack and kidney disease.
All results indicate that this type of exercise had positive affect on health for the subjects of this intervention. The magnitude of health changes seen by using sprint interval training were comparable to those observed after 6 to 8 weeks of conventional endurance exercise training in untrained or moderately trained adults.
What conclusions can we take from this research?
Earlier studies conducted on young, fit, normal-weight men concluded that sprint interval training can improve cardiorespiratory fitness  and insulin sensitivity. This study concurs that sprint interval training has a positive affect on health and that additional benefits in body composition and blood pressure are also seen when sprint interval training is applied to overweight/obese sedentary populations.
While sprint interval training involves very short efforts of physical exercise, the 4-5 minute rest times between efforts makes the total session duration comparable to the 30 minutes stated in physical activity guidelines. Although the time excising is a fraction of the time of moderate intensity activity, the time taken to complete the sprint interval session does not make it any more viable as a time saving exercise. Despite this, further research into sprint interval training in which diet and all physical activity are controlled is still important in order to see the direct affects of the sprint interval training.
Two of the authors of this study; Whyte and Gill have conducted further study into determining the shortest exercise with significant health benefits. Their later study has concluded that a maximal extended sprint, not sprint interval training is the most time efficient exercise for overweight/obese individuals.
This intervention has shown significant health benefits for overweight/obese individuals, however, informed decision making needs to be practiced when considering high intensity activity for this population. Exercise specialists need to consider motivation, adherence and above all else safety. Pre-exercise screening must be followed to identify individuals at an elevated risk of having an adverse event in response to exercise.
Current physical activity guidelines from:
Information on the benefits of high intensity interval training.
Exercise and Sports Science Australia pre-exercise screening tool.
If you have a chronic health condition and are unsure of how to begin an exercise program, an exercise physiologist is the best allied health professional to help you safely begin your exercise journey.
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