The Effect of High-Intensity Interval Training Type on Body Fat Percentage, Fat and Fat-Free Mass: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

Abstract

This systematic review and meta-analysis of randomized controlled trials (RCTs) compared body compositional changes, including fat mass (FM), body fat percentage (BF%), and fat-free mass (FFM), between different types of high-intensity interval training (HIIT) (cycling vs. overground running vs. treadmill running) as well as to a control (i.e., no exercise) condition. Meta-analyses were carried out using a random-effects model. The I2 index was used to assess the heterogeneity of RCTs. Thirty-six RCTs lasting between 3 to 15 weeks were included in the current systematic review and meta-analysis. RCTs that examined the effect of HIIT type on FM, BF%, and FFM were sourced from online databases including PubMed, Scopus, Web of Science, and Google Scholar up to 21 June 2022. HIIT (all modalities combined) induced a significant reduction in FM (weighted mean difference [WMD]: −1.86 kg, 95% CI: −2.55 to −1.18, p = 0.001) despite a medium between-study heterogeneity (I2 = 63.3, p = 0.001). Subgroup analyses revealed cycling and overground running reduced FM (WMD: −1.72 kg, 95% CI: −2.41 to −1.30, p = 0.001 and WMD: −4.25 kg, 95% CI: −5.90 to −2.61, p = 0.001, respectively); however, there was no change with treadmill running (WMD: −1.10 kg, 95% CI: −2.82 to 0.62, p = 0.210). There was a significant reduction in BF% with HIIT (all modalities combined) compared to control (WMD: −1.53%, 95% CI: −2.13, −0.92, p = 0.001). All forms of HIIT also decreased BF%; however, overground running induced the largest overall effect (WMD: −2.80%, 95% CI: −3.89 to −1.71, p = 0.001). All types of HIIT combined also induced an overall significant improvement in FFM (WMD: 0.51 kg, 95% CI: 0.06 to 0.95, p = 0.025); however, only cycling interventions resulted in a significant increase in FFM compared to other exercise modalities (WMD: 0.63 kg, 95% CI: 0.17 to 1.09, p = 0.007). Additional subgroup analyses suggest that training for more than 8 weeks, at least 3 sessions per week, with work intervals less than 60 s duration and separated by ≤90 s active recovery are more effective for eliciting favorable body composition changes. Results from this meta-analysis demonstrate favorable body composition outcomes following HIIT (all modalities combined) with overall reductions in BF% and FM and improved FFM observed. Overall, cycling-based HIIT may confer the greatest effects on body composition due to its ability to reduce BF% and FM while increasing FFM.

Effects of a 16-Week Training Program with a Pyramidal Intensity Distribution on Recreational Male Cyclists

“…In the meta-analysis report by Fatemeh Khodadadi et al [ 24 ], resulting from the analysis of cycling intervention studies with HIIT (training protocols duration between 3 and 15 weeks), the weighted mean effect was −1.72 kg for fat mass, −0.92% for fat mass percentage, and an increase of 0.63 kg for fat-free mass. In the present study, the reduction was −1.87 kg (−11.78%) for fat mass, −10.07% for fat mass percentage, an increase of 0.35 kg (0.61%) (not significant) for lean mass, and 1.95% for lean mass percentage.…”

“…The differences observed between the present study and the interventions with HIIT could be due to the great disparity of TID, the duration of the training protocols, and the fact that HIIT is much more stressful and does not allow a large training volume. Therefore, Z1 and Z2 training time may have had a greater effect on reducing fat mass in the present study, and HIIT, while also contributing to fat mass loss, appears to have a greater effect on increasing fat-free mass [ 24 , 25 ].…”

Exercise Effects on Health-Related Quality of Life (HRQOL), Muscular Function, Cardiorespiratory Function, and Body Composition in Smokers: A Narrative Review

“…During exercise training, a significant decrease in the amount of fat-free mass, total body, and visceral fat occurs with an overall reduction of the whole-body mass [46]. Additional evidence has supported that significant changes are associated with the duration and intensity of training, with notable differences in body mass, BMI, waist circumference, fat-free mass, fat mass, and percentage of body fat, with rates of fat oxidation in grams per day increasing during training [31].…”

“…Early studies noted that fat metabolism is higher during moderate continuous training [39][40][41][42][43], with a recent study suggesting a higher total fat oxidation quantity after a HIIT session [26]. HIIT assists in improving the body composition by increasing body and skeletal muscle fatty acid oxidation and the inhibition of appetite and facilitating the release of corticotrophin hormone [37,46]. Moreover, there are some reasons to believe that the excess post-exercise oxygen consumption (EPOC) might assist in post-exercise fat metabolism [44].…”

“…Although these changes are observable during endurance training, it is less dominant and slower than when performing HIIT. Recent studies have taken note of endurance training individuals having a high energy expenditure, which could be caused by a sufficient EPOC [46,47]. Therefore, a linear relationship exists between the EPOC magnitude and exercise intensity in determining whether body composition and weight improvements will occur [48].…”