Literature Review: High-Intensity Interval Training and Fat Loss

High-Intensity Interval Training and Fat Loss

           In the health and fitness industry, body composition (specifically body fat loss) has been the topic of much research and discussion (Clark, Rosa, DeRevere, & Astorino, 2019; Maillard, Pereira, & Boisseau, 2018; Roy, Meredith-Jones, Osborne, Taylor, Jospe, Williams, & Brown, 2018). While there are different ways to promote fat loss (lipolysis) through physical activity, cardiovascular training is regarded as the most efficient method to enhance fat loss (Shehata & Mahmoud, 2018). As a form of exercise, cardiovascular training can be broken down into two basic structures: moderate-intensity (or continuous training) and high-intensity interval training (HIIT) (Viana, Naves, Coswig, de Lira, Barbosa, Steele, Fisher, & Gentil, 2019). Moderate-intensity training consists of prolonged bouts of exercise done below one’s maximum heart rate; conversely, HIIT utilizes short, fast-paced intervals done near one’s maximum heart rate (Viana et al., 2019).

            Beliefs held by health care and fitness professionals indicate that, “there is still no consensus as to which training method is best to reduce body fat” (Viana et al., 2019, p. 656). The human body is a highly adapted organism that can carry out many complex functions (Purkart, Simunic, & Gerzevic, 2015). Understanding more about the body’s response to exercise could have a significant impact in several different areas including health care, fitness and personal training, education, and athletics.

           Due to the widespread variability of HIIT and moderate-intensity protocols, differentiated testing methods, and lack of adherence to exercise programs, there is no clear-cut answer as to which form of cardiovascular training is most beneficial for promoting fat loss (Viana et al., 2019; Maillard et al., 2018). These issues present some significant gaps in the literature. Therefore, this literature review will examine three different types of research—meta  analysis, studies done with obese participants, and studies done with randomized participants—to  help determine which type of cardiovascular exercise is most effective for reducing overall body fat percentage.

Procedure (Wedan, 2019)

              This literature review focused on finding scholarly, peer-reviewed research on the effects of high-intensity interval training on fat loss. The databases used for this review include: SPORTDiscus, MEDLINE, Directory of Open Access Journals, and the university’s Library One Search. The following keywords were used to search the databases: HIIT, high-intensity interval training, steady-state cardio, cardio, fat loss, body fat, weight loss, fat reduction, and body composition. While the initial search generated over 30,000 results, these numbers were reduced to just over 200 after adding further database search limiters. After a thorough reading of the research, there were 15 journal articles selected to be used in this review.

Inclusion and Exclusion Criteria (Wedan, 2019)

                The selected articles were evaluated based on their relevance and accessibility. The articles were either retained or discarded based on the inclusion and exclusion criteria described below. All of the articles needed to meet the following inclusion criteria: 1) be published between 2012-2019, 2) be a peer-reviewed and present empirical data, 3) be written in English, 4) be accessible through the university library, and 5) discuss high-intensity interval training and fat loss as a main theme. Articles were discarded based on the following exclusion criteria: 1) published earlier than 2012, 2) not written in English, and 3) not empirically derived data. Of the 15 articles identified, 10 articles met the inclusion criteria and were used in the review. 

Review of Literature

Meta-Analysis

              From the literature search, four meta-analysis articles were selected. In the first article, Maillard et al. (2017) assessed “the efficacy of HIIT in reducing total, abdominal, and visceral fat mass in normal-weight and overweight/obese adults” (p. 269). This analysis was conducted using nearly four decades worth of research and examined the effects of high-intensity running and cycling protocols (Maillard et al., 2017). In the second article, Viana et al. (2019) compared “the effects of interval training and moderate-intensity continuous training (MOD) on body adiposity in humans” (p. 655). The authors utilized nearly 800 articles and rigorous eligibility criteria for selecting their studies (Viana et al., 2019). The third meta-analysis focused on training methods that promoted the highest rates of lipid oxidation (Purkart et al., 2015). A review of 172 articles compared the effects of prolonged, moderate-intensity exercise to low volume, high-intensity interval training (Purkart et al., 2015). Lastly, Turk et al. (2017) investigated high-intensity training and obesity. As the first study of its kind, the authors analyzed the “effectiveness of HIIT on cardiopulmonary fitness and body composition in adults with obesity compared to traditional (high volume continuous) exercise” (Turk et al., 2017, p. 258).

             The meta-analysis studies provided a comprehensive overview of the research topic. As a group, these articles shared some strengths and weaknesses. To the researchers’ credit, each of the meta-analyses provided a thorough set of inclusion and exclusion criteria for the selected articles (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). For example, Viana et al. (2019) explained:

Studies that met the following criteria were included: (1) original articles, (2) human trials, (3) minimum exercise duration of 4 weeks, and (4) directly or indirectly compared interval training with MOD as the primary or secondary aim. (p. 655)

           Another shared strength of the meta-analyses was the widespread and diverse use of electronic databases (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). Search results were generated from reputable sources such as PubMed, Google Scholar, Scopus, Web of Science, Cochrane Library, Pedro, and Embase (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). Additionally, several different languages were utilized in the search process including English, Spanish, Portuguese, and Dutch (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). Along with these strengths, the meta-analyses also shared a common weakness: none of the studies were able to find a unified set of testing protocols for high-intensity training (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). In their research, Maillard et al. (2017) summarized that “owing to the wide variety of protocols used and the lack of full details about cycling training, further comparisons need to be made” (p. 269).

            When compared to the other two types of studies used in the literature review (studies using obese participants and studies using randomized participants), the meta-analyses conveyed similar findings and results (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). The collective research indicated that short sessions of high-intensity training promoted greater reductions in body fat than prolonged bouts of low or moderate-intensity cardiovascular exercise (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). This consistency in the research is noteworthy and could hold important implications in future health and wellness practices.

HIIT and Obese Participants

          Another theme that emerged from the literature was how HIIT effects fat loss in obese participants. Three articles were selected that addressed this topic. In the first article, Clark et al. (2019) examined the “effects of two high-intensity interval training (HIIT) regimens” on oxygen uptake, body composition, and strength in sedentary, obese women (p. 879). The study observed 17 women over a 6-week period (Clark et al., 2019). The second article studied the long-term prognosis of a HIIT intervention for obese adults (Roy et al., 2018). Two hundred and fifty participants were observed over a 12-month period and could select either a high-intensity or moderate-intensity exercise program (Roy et al., 2018). The third study looked at the behavioral patterns of sedentary, obese males after being exposed to HIIT and moderate-intensity training programs (Santos, Browne, Souza, Matos, Macedo, Farias-Junior, Farias-Junior, Costa, & Fayh, 2019). The authors studied 17 participants and analyzed whether their participation in HIIT would encourage them to adopt a more physically active lifestyle (Santos et al., 2019).

             The studies done by Clark et al., Roy et al., and Santos et al. give a unique perspective on HIIT and its relation to body composition. As obesity rates continue to increase across North America, fewer and fewer adults are meeting the recommended requirements for daily physical activity (Clark et al., 2019). Studies like these could have a significant impact on future exercise recommendations. As such, the three articles shared some similar strengths and weaknesses. Each of the studies employed a detailed selection process for its participants (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019). In their research, the authors accounted for different variables that might have influenced results (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019). Factors such as age, body mass index, current and previous medication, general physical readiness, blood pressure, and pre-existing conditions were accounted for during the selection process (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019). Although the studies were generally well-organized, two significant weaknesses were identified. In the study done by Clark et al. (2019), all the HIIT protocols were conducted on stationary bicycles; this limited the overall scope of the exercise program and left unanswered questions about other types of HIIT and fat loss. In a different study, Roy et al. (2018) did not account for the eating habits and caloric intake of their participants, thus risking outside factors influencing the results.

          When analyzed alongside the meta-analyses and randomized participant trials, the articles studying HIIT and obese participants concluded similar results (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019). Although the methodologies for the studies were not as strong as those used in the meta-analyses, the authors presented a compelling case for why HIIT is beneficial for obese persons trying to lose body fat.

HIIT and Randomized Participants

           The third theme found in the literature was how HIIT impacts fat loss in a randomized group of participants. Again, three articles were selected that addressed this topic. In the first article, Ahlert, Matzenbacher, Albarello, and Halmenschlager (2019) studied the relationship between “excess post-exercise oxygen consumption and recovery energy expenditure between high-intensity interval aerobic exercise (HIIT) and continuous aerobic exercise” (p. 20). The authors studied adult male runners and tracked their lipid metabolism after bouts of exercise (Ahlert et al., 2019). The second study explored “whether high-intensity interval training is an alternative time-efficient strategy for improving body composition and muscle strength in young women” (Carneiro, de Oliveira, Martins, Souza, Nunes, & Orsatti, 2017, p. 105). The researchers randomly assigned 25 women to two exercise groups (HIIT or aerobic and resistance training) and observed their progress over a 12-week period (Carneiro et al., 2017). In the final study, Shehata and Mahmoud (2018) explored the effects of “high-intensity interval training (HIIT) on weight, body mass index and body fat percentage in adults” (p. 125). The authors selected 40 untrained participants, half of whom engaged in a HIIT program three days per week for three months (Shehata & Mahmoud, 2018).

          After a thorough analysis, each of the studies contained several significant weaknesses. In the first article, Ahlert et al. (2019) only used experienced male runners as their participants. Using such a highly-trained homogenous group limits the study’s practical application to everyday populations. Similarly, Carneiro et al. (2017) used only female participants in their research. Again, this approach narrows the significance and use of the findings. Interestingly, Shehata and Mahmoud (2018) did not specify the sex of their participants. Additionally, the authors only explain the training protocols, results, and conclusions for the HIIT group; they do not give any information on the other half of the participants in the study (Shehata & Mahmoud, 2018). While each of the randomized participant articles did utilize sound testing protocols, the combined weaknesses of the studies overshadow the collective strengths.

             While the randomized participant studies delivered similar results to the other two article groups, it was surprising to see some of the studies appearing in academic literature. Although the meta-analysis studies and obese participant articles were not perfectly designed, their shortcomings did not seem as glaring or potentially impactful as those found in the randomized participant studies. Fortunately, despite the inconsistencies, all three of the themes found in the literature present a common message: HIIT, when performed correctly and consistently, can have significant benefits for overall fat loss (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019; Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017; Ahlert et al., 2019; Carneiro et al., 2017; Shehata & Mahmoud, 2018).

Conclusions and Recommendations

            This literature review compared the findings of ten studies on the topic of HIIT and fat loss. The selected articles were categorized into three distinct themes: meta-analysis, HIIT and obese participants, and HIIT and randomized participants. Overall, the results showed consistent findings—HIIT  can be a time-effective method for lowering body fat percentage (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019; Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017; Ahlert et al., 2019; Carneiro et al., 2017; Shehata & Mahmoud, 2018). Thus, the literature review was consistent with the original research question.

          After reading the various articles for this review, two aspects of the literature stood out. First, in nearly all of the studies, the inclusion and exclusion criteria provided a sophisticated filter for the researchers (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019; Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017; Ahlert et al., 2019; Carneiro et al., 2017; Shehata & Mahmoud, 2018). Even in the meta-analyses, the methods of processing which articles would be used was both thorough and effective (Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017). This is significant because it strengthened the credibility of the author’s research. Second, only a single study found results that supported their null hypothesis. Santos et al. (2019) concluded that exposing adult males to single bouts of HIIT did not elicit any significant changes in daily sedentary behaviors. This was contrary to their original hypothesis which predicted:

That the inactive obese males would decrease their habitual physical activity levels and increase their sedentary levels similarly following a single low-volume HIIE and MICE sessions compared to a day without exercise. (p.391)

           It is important to note that the authors of this study did not actually measure the effects of HIIT on body composition; rather, they approached HIIT from a psychological perspective and used it to assess human behaviour. Regardless, it was surprising to see that virtually every study found results that supported their initial hypothesis. The studies in the literature review provided strong evidence to help answer the original research question.

          Despite the unified findings, there were two significant limitations found across multiple studies. First, the studies did not always use comparable testing protocols for their HIIT and moderate-intensity exercises. Some studies had participants only riding stationary bikes while others had participants using bodyweight-only exercises, running wind sprints, working out with weights, or walking on a treadmill (Clark et al., 2019; Carneiro et al., 2017; Ahlert et al., 2019; Shehata & Mahmoud, 2018; Santos et al., 2019). Although HIIT can be generally categorized as “brief bouts of intense exercise >80% of maximum heart rate (HR max), followed by periods of low-intensity workouts or rest” (Carneiro et al., 2017, p. 106), it was unclear from the literature whether certain HIIT protocols had a greater effect on fat loss. In future research, having a unified set of testing procedures could help address this issue. Another cross-study limitation was the self-reporting standards used in some of the studies. In two of the articles examining HIIT and obesity, participants were asked to carry out some of the testing protocols outside of the clinical environment (Clark et al., 2019; Roy et al., 2018). This was problematic because of the increased possibility of experimental error. Roy et al. (2018) noted that by the end of their 12-month study, 73% of their participants had stopped reporting their data. If studies on HIIT and fat loss are conducted in the future, it would be wise to have the testing procedures administered in a clinical experimental setting.

              After reviewing the findings in the literature, it was clear that HIIT is an effective alternative to moderate-intensity cardiovascular training for reducing body fat (Clark et al., 2019; Roy et al., 2018; Santos et al., 2019; Maillard et al., 2017; Viana et al., 2019; Purkart et al., 2015; Turk et al., 2017; Ahlert et al., 2019; Carneiro et al., 2017; Shehata & Mahmoud, 2018). The results of this literature review could have significant real-world implications. These results could impact several important industries including healthcare, athletics, psychology, sociology, and education. Physical therapists could alter their rehabilitation programs, team trainers might adjust their training periodization, and physical education teachers could encourage students to explore different types of cardiovascular exercise. Many positive implications could arise from this research. Hopefully, continued investigation into the field of exercise science and body composition will lead to an improved quality of life for people around the world.

References

Ahlert, M., Matzenbacher, F., dos, S. A., & Henrique Halmenschlager, G. (2019). Comparison of epoc and recovery energy expenditure between hiit and continuous aerobic exercise training. Revista Brasileira De Medicina do Esporte, 25(1), 20-23.

Carneiro, M. A. S., de Oliveira, A. A., Martins, F. M., Souza, A. P., Nunes, P. R. P., & Orsatti, F. L. (2018). High-intensity interval body weight training promotes different adaptations to combined training in body composition and muscle strength in young women. Science & Sports, 33(3), 105-113. doi:10.1016/j.scispo.2017.11.001

Clark, A., Rosa, D. L., DeRevere, J. L., & Astorino, T. A. (2019). Effects of various interval training regimes on changes in maximal oxygen uptake, body composition, and muscular strength in sedentary women with obesity. European Journal of Applied Physiology, 119(4), 879-888.

Maillard, F., Pereira, B., & Boisseau, N. (2018). Effect of high-intensity interval training on total, abdominal and visceral fat mass: A meta-analysis. Sports Medicine (Auckland, N.Z.), 48(2), 269-288. doi:10.1007/s40279-017-0807-y

Purkart, B., Simunic, B., & Gerzevic, M., (2015). An overview of training methods that promote the highest lipid oxidation during and after a single exercise session. Annales Kinesiologiae, 6(2), 93-118.

 

Roy, M., Meredith-Jones, K., Osborne, H., Taylor, R. W., Jospe, M., Williams, S. M., & Brown, R. C. (2018). High-intensity interval training in the real world: Outcomes from a 12-month intervention in overweight adults. Medicine & Science in Sports & Exercise, 50(9), 1818-1826.

Santos, V., Browne, R., Souza, D., Matos, V., Macêdo, G., Farias-Junior, L., Farias-Júnior, J., Costa, E., & Fayh, A. (2019). Effects of high-intensity interval and moderate-intensity continuous exercise on physical activity and sedentary behavior levels in inactive obese males: A crossover trial. Journal of Sports Science and Medicine, 18, 390-398.

Shehata, A., & Mahmoud, I. (2018). Effect of high intensity interval training (hiit) on weight, body mass index and body fat percentage for adults. Ovidius University Annals, Series Physical Education & Sport/Science, Movement & Health, 18(2), 125-130.

Strong, H. (2018). Assignment #2 example (literature review search) [PDF file]. Retrieved from https://learn.twu.ca/pluginfile.php/227436/mod_assign/introattachment/0/Assignment%20%232%20Example%20%28Literature%20Review%20Search%29.pdf?forcedownload=1

Turk, Y., Theel, W., Kasteleyn, M. J., Franssen, F. M. E., Hiemstra, P. S., Rudolphus, A., Taube, C., & Braunstahl, G. J. (2017). Obesity Science & Practice, 258-271. doi:10.1002/osp4.109

Viana, R. B., Naves, J. P. A., Coswig, V. S., de Lira, C., Barbosa, A., Steele, J., Fisher, J. P., & Gentil, P. (2019). Is interval training the magic bullet for fat loss? A systematic review and meta-analysis comparing moderate-intensity continuous training with high-intensity interval training (HIIT). British Journal of Sports Medicine, 53(10), 655-664. doi:10.1136/bjsports-2018-099928

Wedan, W. (2019). Literature review search (Unpublished essay). Trinity Western University, British Columbia.