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)

Abstract

ObjectivesTo compare the effects of interval training and moderate-intensity continuous training (MOD) on body adiposity in humans, and to perform subgroup analyses that consider the type and duration of interval training in different groups.DesignSystematic review and meta-analysis.Data sourcesEnglish-language, Spanish-language and Portuguese-language searches of the electronic databases PubMed and Scopus were conducted from inception to 11 December 2017.Eligibility criteria for selecting studiesStudies that met the following criteria were included: (1) original articles, (2) human trials, (3) minimum exercise training duration of 4 weeks, and (4) directly or indirectly compared interval training with MOD as the primary or secondary aim.ResultsOf the 786 studies found, 41 and 36 were included in the qualitative analysis and meta-analysis, respectively. Within-group analyses showed significant reductions in total body fat percentage (%) (interval training: −1.50 [95% CI −2.14 to −0.86, p<0.00001] and MOD: −1.44 [95% CI −2.00 to −0.89, p<0.00001]) and in total absolute fat mass (kg) (interval training: −1.58 [95% CI −2.74 to −0.43, p=0.007] and MOD: −1.13 [95% CI −2.18 to −0.08, p=0.04]), with no significant differences between interval training and MOD for total body fat percentage reduction (−0.23 [95% CI −1.43 to 0.97], p=0.705). However, there was a significant difference between the groups in total absolute fat mass (kg) reduction (−2.28 [95% CI −4.00 to −0.56], p=0.0094). Subgroup analyses comparing sprint interval training (SIT) with MOD protocols favour SIT for loss of total absolute fat mass (kg) (−3.22 [95% CI −5.71 to −0.73], p=0.01). Supervised training, walking/running/jogging, age (<30 years), study quality and intervention duration (<12 weeks) favourably influence the decreases in total absolute fat mass (kg) observed from interval training programmes; however, no significant effect was found on total body fat percentage (%). No effect of sex or body mass index was observed on total absolute fat mass (kg) or total body fat percentage (%).ConclusionInterval training and MOD both reduce body fat percentage (%). Interval training provided 28.5% greater reductions in total absolute fat mass (kg) than MOD.Trial registration numberCRD42018089427.

Mechanistic and methodological perspectives on the impact of intense interval training on post‐exercise metabolism

“…Recent work has identified small to moderate improvements in body composition following HIIT/SIT that are similar to and, in some cases, greater than that which is seen following MICT. Indeed, a recent meta‐analysis indicated that while MICT, HIIT, and SIT are similarly effective at reducing body fat percentage, interval training results in superior reductions in total absolute fat mass by ~28.5% compared to MICT . Others have reported equal effectiveness at reducing total body fat percentage and absolute fat mass, though only when protocols are matched for total work .…”

“…Indeed, a recent meta-analysis indicated that while MICT, HIIT, and SIT are similarly effective at reducing body fat percentage, interval training results in superior reductions in total absolute fat mass by ~28.5% compared to MICT. 12 Others have reported equal effectiveness at reducing total body fat percentage and absolute fat mass, though only when protocols are matched for total work. 64 When protocols are not matched, MICT tends to produce greater reductions in total body fat percentage compared to HIIT and SIT as a whole, though Wingate-based SIT (performed in an "all-out" manner) on its own produces body fat reductions comparable to MICT in less time.…”

“…Both types of exercise result in similar aerobic adaptations to traditional moderate‐intensity continuous training (MICT), as well as anaerobic benefits unique to this modality . Importantly, these training adaptations are achieved with a lower‐time commitment and exercise volume than MICT, and despite this reduction in training volume, it includes improvements in body composition …”

“…3,6,8 Importantly, these training adaptations are achieved with a lower-time commitment and exercise volume than MICT, 2,7,9 and despite this reduction in training volume, it includes improvements in body composition. 4,[10][11][12] An important factor to consider is the magnitude and duration of the oxygen uptake (VO 2 ) response that occurs after cessation of both interval and continuous training. During exercise, V O 2 elevates to support the increased energy demand and remains elevated after exercise, resulting in a V O 2 above baseline.…”

Resistance High-Intensity Interval Training (HIIT) Improves Acute Gluconeogenesis from Lactate in Mice

“…High-Intensity Interval Training (HIIT) is characterized by repeated high-intensity, short-duration exercises intercalated with active recovery (low-intensity exercise) or rest. In aerobic protocols -which are more common -HIIT exercises reach heart rates above 80% the maximum, or oxygen consumption above 85% the VO 2peak [10][11][12]. HIIT is effective in improving performance and physical conditioning, cardiovascular health and in modifying the muscle energy metabolism.…”