Exercise as it relates to Disease/HIIT or Prolonged Continuous Exercise- Which is better for obese young women?

This fact sheet is in response to the research article "Comparable Effects of High-Intensity Interval Training and Prolonged Continuous Exercise Training on Abdominal Visceral Fat Reduction in Obese Young Women" by Zhang and colleagues (2017).

What is the background to this research?
Obesity is a worldwide issue that continues to have significant health and financial repercussions. Most commonly measured using BMI, obesity not only depends on the balancing of calorie intake and expenditure but also on the composition of adipose tissue in the body. Moderate intensity continuous training (MICT) has been used as a training method to help reduce body mass index (BMI), reduce adiposity, and improve aerobic fitness for many decades. Exercise performed at around 60% of an individual’s VO2 max for a duration of at least 30 minutes is considered to be MICT. In recent years however, high intensity interval training (HIIT) has been frequently researched and commonly used as an alternative exercise method to MICT in the prevention and reduction of obesity. This training method consists of short bursts of near maximal intensity exercise (90-95% VO2 max) broken up by a rest period. These work and rest periods are repeated for the duration of the exercise which is generally less than 30 minutes.

Despite the growing popularity of HIIT, the benefits of HIIT over MICT are relatively unknown with different research proving mixed results. This study by Zhang and colleagues aims to add to this research by comparing the two training methods in their effectiveness in an obese female population.

Where is the research from?
The research was conducted by Zhang and six other colleagues from China, Hong Kong and Australia. Several of the authors have worked together previously on similar research. The study was conducted in Shijiazhuang, China and was published in the Journal of Diabetes Research in 2017.

What kind of research was this?
The research was a quantitate randomized control trial with two experimental groups and one control group.

What did the research involve?
Fifty-two 18-22-year-old obese (defined as BMI  25kg/m2 in this study) female university students were recruited to the study. Participants were recruited based upon their meeting of a number of health and lifestyle based selection criteria. From the 52 recruits, 5 declined participation and 4 did not complete the programs, leaving 43 participants who completed the study.

Participants were randomly selected into either a twelve-week moderate intensity continuous training (MICT) program, high intensity interval training (HIIT) program, or a control group where no exercise was performed. The MICT program involved participants exercising at 60% of their VO2 Max until they reached the required work output. The HIIT program involved participants exercising at 90% of their VO2 max for 4 minutes, followed by 3 minutes of passive recovery. This was repeated until the required work output was reached. All exercises were performed on a cycle ergometer (stationary bike).

A number of body composition measurements were taken before and after the program and aerobic tests were performed pre and post intervention and at the end of the fourth and eighth weeks. These measurements included total body mass, body fat percentage, fat mass, abdominal visceral and subcutaneous fat area, and VO2 max.

What were the basic results?
Zhang and colleagues found that after completing the 12-week program both the MICT and HIIT groups had achieved reductions in their body mass, body fat percentage, fat mass, and abdominal fat area. MICT and HIIT groups also improved their aerobic capacity. No changes in these measures occurred in the control group, and there was no significant difference in the improvements between the MICT and HIIT groups.

Overall the results show that MICT and HIIT are effective reducing body fat, fat mass, and abdominal fat area in obese young women. They also demonstrate that there is no difference in the results achieved between MICT and HIIT programs when the same work output is achieved.

What conclusions can we take from this research?
From this research we can conclude that MICT and HIIT are both effective training methods to improve aerobic capacity and reduce body fat, fat mass, and abdominal fat area. While obese female university students were used for this study, similar results have been found in the same and different populations.

While this study found no significant difference in HIIT and MICT, other studies have found that HIIT produces better results against other biological measures .This is important to consider when applying these methods to other populations that wish to achieve different results.

We can also conclude that in an obese population there is no significant difference in the effectiveness of MICT or HIIT to improve aerobic fitness and reduce overall fatness. However, because HIIT produces similar results to MICT in significantly less exercise time it may be a preferred training method with time poor individuals.

Practical advice
MICT and HIIT can be used by both obese, overweight or healthy individuals to help reduce body mass, body fat percentage, fat mass, and abdominal fat area. As HIIT produces the same results as MICT but with less exercise time it may be a more popular training method for time poor individuals.

However, it is important to note that due to the many health effects associated with overweight and obesity it is important for individuals to visit their doctor and complete a pre-exercise screening before they adopt any exercise program.

Further information

 * World Health Organization fact sheet on overweight and obesity http://www.who.int/mediacentre/factsheets/fs311/en/
 * What is VO2 Max? https://www.verywell.com/what-is-vo2-max-3120097
 * Exercise and Sport Science Australia pre-exercise screening tool https://www.essa.org.au/wp-content/uploads/2011/09/Screen-tool-version-v1.1.pdf