Exercise as it relates to Disease/The effects of HIIT on aerobic fitness, cardiac function and insulin resistance in healthy older adults
This Wikibook page presents a critical appraisal of the research article: "Novel all-extremity high-intensity interval training improves aerobic fitness, cardiac function and insulin resistance in healthy older adults".
What is the background to this research?
Age is a considerable risk factor for cardiovascular disease (CVD) and other related diseases. Therefore, improving and maintaining cardiovascular fitness is an important consideration with age. Previous studies have shown improved cardiovascular health lowers mortality and reduces risk of developing CVD and related diseases.
High-intensity interval training (HIIT), in many forms, has been shown to improve CV health and insulin resistance in a wide range of age groups and health levels, including older people. Specifically, treadmill and bike ergometer HIIT protocols have been used previously in studies focusing on older adults. According to the researchers, although previous studies have been done on the effects of HIIT training in older adults, this is the first study to focus on the effects of specifically all-extremity non weight bearing HIIT. Therefore, a benefit of this study is that it has filled a previous gap in knowledge, while simultaneously building on current knowledge from similar research.
Where is the research from?
The study was conducted in 2016 at the University of Florida, located in Gainesville FL, United States. Specifically, the interventions were performed at the Integrative Cardiovascular Physiology laboratory, in the Centre for Exercise Science. It is unclear as to whether there is any underlying motive for this research.
What kind of research was this?
The study design was a randomised controlled parallel group study consisting of a control group (CONT, n = 14) as well as two exercise groups (MICT, n = 14 and HIIT, n = 15). Participants who met the selection criteria were assigned a group randomly based on a computer random number generator.
The research hypothesis was "8 weeks of all extremity HIIT will be more effective in improving aerobic fitness, cardiac function, and metabolic risk factors compared to all extremity MICT in healthy older adults".
Randomised control studies are widely used in scientific research. Randomisation allows for reduced bias, as researchers are unable to choose participants for each group based on certain characteristics that may be favourable for supporting the hypothesis. The aim of randomisation like this is to improve the chance that the research groups are representative of the general population, and therefore, the results are likely to be representative of the general population as well. The use of a control group aims to "prove" that the research intervention was the cause of any changes in the research groups, and that results were not due to chance or some other variable. These two aspects improve the strength of this research.
This study was a "between subjects" design, meaning participants were assigned to only one group and were not subject to both interventions. This increases the possibility of an error as it does not acount for the variability between each individual. This can result in skewed data.
The study also had a fairly low sample size, with only 43 participants split into 3 groups, only 17 of which were male. Low sample size reduces the external validity, that is, the likelihood that the results will be representative of the general population. The larger female participation may have also skewed the results, again reducing the external validity of the study.
What did the research involve?
The research aimed to measure the feasibility of HIIT training as an intervention for the declining aerobic fitness, cardiac function and other metabolic risk factors seen with age.
Both HIIT and MICT groups performed their exercise on a non-weight bearing, all-extremity ergometer. Exercise was performed 4 days per week for 8 weeks. Both groups performed a 10 min warmup and a 5 min cool down at 70% HR peak and both underwent a period of familiarisation/ pre conditioning before the trial. Allowing participants to familiarise/pre condition themselves to the exercise reduces the likelihood that the results will be due to "practice effects". This is the tendency for participants to become better at a task because they have become familiar with it, rather than because the intervention has caused a change. This improves the strength of this research.
The HIIT protocol consisted of "4 x 4 minute intervals at 90% of HR peak interspersed with 3 x 3-minute active recovery intervals at 70% HR peak" – 25 min total. Previous research has demonstrated that HIIT protocols with intensities of 85-95% of HR peak induce significant improvements across a range of age groups. Therefore, the design of this specific HIIT protocol is supported by previous research.
The MICT protocol consisted of 32 minutes at 70% HR peak.
|Aerobic Fitness and Caloric Expenditure||Measured using open-circuit spirometry during a maximal graded test on a treadmill. 6 min warmup at 70-80% of age predicted HR max with 2.5% increase every 2 mins after warmup until exhaustion.||Open-circuit spirometry is a comprehensive way of testing aerobic fitness.||Requires participants to work at their maximum which may rule out participants with other health conditions.|
|Cardiac Function||Transthoracic echocardiogram used to measure LV wall thickness and internal dimensions.||Non-invasive, comprehensive and very commonly used.||-|
|Body Composition||Height measured using a stadiometer, weight measured using electric scales, fat and fat-free mass measured using dual-energy x-ray absorptiometry (DXA).||DXA is widely regarded as the "gold standard" in body composition measurement.||-|
|Lipids, Glucose and Insulin||Levels were determined from analysis of fasting blood samples.||-||-|
|Resting Blood Pressure||Measured automatically using Dinamap GE.||Quick and easy.||-|
|Habitual Physical Activity||Participants wore an accelerometer for 4 consecutive days (3 weekdays and 1 weekend day).||Measuring habitual activity helps to show that research results were not due to variables outside of the intervention such as other exercise.||A 4-day physical activity log may not be sufficient to infer typical weekly physical activity over several weeks or months.|
What were the basic results?
|Caloric Expenditure||Similar between HIIT and MICT|
|Aerobic Fitness||Improved only in HIIT ~11%|
|Cardiac Contractile Function||Improved only in HIIT ~4%|
|Insulin Resistance||Decreased only in HIIT 26%|
|Left Ventricular Morphology and Diastolic Function||Unchanged in all groups|
|Fasting Blood Glucose and Lipids||Unchanged in all groups|
|Body Weight, BMI and Body Composition||Unchanged in all groups|
The research also found a significant positive correlation between improvements in cardiac contractile functions and improvements in VO2peak, suggesting a causation relationship between the two.
It is important to note that the study had a mortality rate of 16%, however all cases were unrelated to the intervention. This shows that there was nothing inherent in the study that caused people to drop out.
What conclusions can we take from this research?
This study helps to strengthen existing evidence that aerobic fitness, cardiac function and insulin resistance can be improved in an older population who are free of cardiovascular or other major clinical disease. Specifically, this study showed that non-weight bearing, all extremity HIIT training is a feasible means of improving fitness.
The use of a non-weight bearing intervention has important implications and benefits over traditional treadmill or bike ergometer HIIT protocols for older individuals who may suffer from conditions such as poor balance.
Sedentary but otherwise relatively healthy older adults should aim to improve their cardiovascular and metabolic health with exercise. If possible, supervised HIIT, of the same or similar protocol as the one presented in this study, should be performed 4 days per week (fitness, injury and energy permitting) for similar results as found in this research.
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