Changes in fat oxidation in response to various regimes of high intensity interval training (HIIT)

Abstract

Increased whole-body fat oxidation (FOx) has been consistently demonstrated in response to moderate intensity continuous exercise training. Completion of high intensity interval training (HIIT) and its more intense form, sprint interval training (SIT), has also been reported to increase FOx in different populations. An explanation for this increase in FOx is primarily peripheral adaptations via improvements in mitochondrial content and function. However, studies examining changes in FOx are less common in response to HIIT or SIT than those determining increases in maximal oxygen uptake which is concerning, considering that FOx has been identified as a predictor of weight gain and glycemic control. In this review, we explored physiological and methodological issues underpinning existing literature concerning changes in FOx in response to HIIT and SIT. Our results show that completion of interval training increases FOx in approximately 50% of studies, with the frequency of increased FOx higher in response to studies using HIIT compared to SIT. Significant increases in β-HAD, citrate synthase, fatty acid binding protein, or FAT/CD36 are likely responsible for the greater FOx seen in these studies. We encourage scientists to adopt strict methodological procedures to attenuate day-to-day variability in FOx, which is dramatic, and develop standardized procedures for assessing FOx, which may improve detection of changes in FOx in response to HIIT.

Contextualising Maximal Fat Oxidation During Exercise: Determinants and Normative Values

“…It is likely that training-induced increases in MFO are mediated by adaptations to adipose tissue lipolysis, NEFA transport to skeletal muscle, skeletal muscle NEFA uptake, muscle triglyceride lipolysis, and/or mitochondrial uptake of fatty acids, given fat oxidation may be limited by fatty acid delivery to skeletal muscle or mitochondrial fatty acid uptake (Romijn et al, 1993 , 1995 ; Sidossis et al, 1997 ; Starritt et al, 2000 ; van Loon et al, 2001 ; Spriet, 2014 ). Indeed, alongside long-standing observations of adaptations to fat metabolism in response to moderate-intensity training (Howald et al, 1985 ; Talanian et al, 2010 ; Egan et al, 2011 ), various high-intensity or sprint interval training regimens can also stimulate beneficial adaptations across many steps involved in fat oxidation (Astorino and Schubert, 2017 ), including increased mitochondrial enzyme activity and protein content (Burgomaster et al, 2005 , 2006 , 2007 , 2008 ; Gibala et al, 2006 ), muscle membrane fatty acid transport protein content (Talanian et al, 2007 , 2010 ; Perry et al, 2008 ), and lipolytic enzyme protein content (Talanian et al, 2010 ).…”

“…MFO is generally upregulated in response to exercise training (Mogensen et al, 2009 ; Alkahtani et al, 2013 ; Astorino et al, 2013 ; Besnier et al, 2015 ; Ipavec-Levasseur et al, 2015 ; Lanzi et al, 2015 ; Nordby et al, 2015 ; Rosenkilde et al, 2015 ; Bagley et al, 2016 ; Mora-Rodríguez et al, 2016 ; Tan et al, 2016 ) whilst Fat max typically remains unchanged (Venables and Jeukendrup, 2008 ; Mogensen et al, 2009 ; Alkahtani et al, 2013 ; Ipavec-Levasseur et al, 2015 ; Rosenkilde et al, 2015 ; Bagley et al, 2016 ; Astorino et al, 2017 ; Schubert et al, 2017 ), although increased Fat max has been observed on occasion (Mogensen et al, 2009 ; Lanzi et al, 2015 ; Nordby et al, 2015 ). Training-induced increases in MFO have been consistently observed in sedentary populations (Mogensen et al, 2009 ; Alkahtani et al, 2013 ; Astorino et al, 2013 ; Besnier et al, 2015 ; Ipavec-Levasseur et al, 2015 ; Lanzi et al, 2015 ; Nordby et al, 2015 ; Rosenkilde et al, 2015 ; Mora-Rodríguez et al, 2016 ; Tan et al, 2016 ), but this effect has not always been observed in previously-active populations (Astorino and Schubert, 2017 ; Schubert et al, 2017 ), and remains uninvestigated in endurance-trained athletes.…”

“…However, high CVs (>15%) have been reported with 24-h dietary control (Croci et al, 2014a ). The reason for this disparity in reliability is unclear, but may be related to the effectiveness of the pre-exercise dietary and exercise control measures (Astorino and Schubert, 2017 ). Failing to adequately match pre-exercise muscle glycogen content is likely to impact MFO given muscle glycogen availability is an independent regulator of substrate metabolism during exercise (Hargreaves et al, 1995 ).…”

Effect of High-Intensity Interval Training on Body Composition, Cardiorespiratory Fitness, Blood Pressure, and Substrate Utilization During Exercise Among Prehypertensive and Hypertensive Patients With Excessive Adiposity

“…In the context of obesity, as a relevant HTN comorbidity and a target for exercise, fat oxidation rates have been found to be highest during low-to moderate-intensity exercise [i.e., MICT, moderate x watts of power output cycling (Achten et al, 2002)]. Intriguingly, the major mechanisms of adiposity loss associated with HIIT seem to be related to mitochondrial adaptations in skeletal muscle after HIIT, including an increase in mitochondrial biogenesis, and other molecular adaptations at Kreb's cycle (into mitochondria) as increases in proteins citrate synthase, cytochrome oxidase, or at membranes proteins as fatty acid binding protein (FABP pm ), or fatty acid CD36 (FAT/CD36) among others (Gibala et al, 2012;Astorino and Schubert, 2018). Also, the specific turn-on/turn-off periods in each interval bout in HIIT promote superior hormonal activity [i.e., adrenaline/noradrenaline catecholamines (Boutcher, 2010), and natriuretic peptide (Birjandi et al, 2016)] after exercise than traditional MICT modalities.…”

Supplements and Nutritional Interventions to Augment High-Intensity Interval Training Physiological and Performance Adaptations—A Narrative Review

“…Males have been reported to have greater increases in cardiorespiratory fitness [186], fat loss [187,188], increased mixed muscle protein synthesis [189], and improved metabolic outcomes (e.g., improved glycemic control) [190,191], compared to females. In contrast, one study reported females to have greater improvements in cardiorespiratory fitness [187], while a majority of studies report no effect of sex on cardiorespiratory adaptations [189][190][191][192][193], body composition [187,192,194], or metabolic [187,192,193,[195][196][197] effects of HIIT. Despite these suggested differences, very few well-powered studies directly address sex differences in response to HIIT.…”