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Perspective ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Physiol. | doi: 10.3389/fphys.2019.00909

Optimizing maximal fat oxidation assessment by a treadmill-based graded exercise protocol: when should the test end?

  • 1EFFECTS-262 Research group, Departament of Medical Physiology., University of Granada, Spain
  • 2Promoting Fitness and Health through Physical Activity, Department of Physical Education and Sports, Faculty of Sport Sciences, University of Granada, Spain
  • 3Center for Healthy Aging, University of Copenhagen, Denmark

Maximal fat oxidation during exercise (MFO) and the exercise intensity eliciting MFO (Fatmax) are considered important factors related to metabolic health and performance. Numerous MFO and Fatmax data collection and analysis approaches have been applied, which may have influenced their estimation during an incremental graded exercise protocol. Despite the heterogeneity of protocols used, all studies consistently stopped the MFO and Fatmax test when the respiratory exchange ratio (RER) was 1.0. It remains unknown however whether reaching a RER of 1.0 is required to have an accurate, reliable and valid measure of MFO and Fatmax. We aimed to investigate the RER at which MFO and Fatmax occurred in sedentary and trained healthy adults. A total of 177 sedentary aged between 18-65 years participated in the study. MFO and Fatmax were calculated by an incremental graded exercise protocol before and after 2 exercise-based intervention. Our findings suggest that a graded exercise protocol aiming to determine MFO and Fatmax could end when a RER=0.93 is reached in sedentary healthy adults, and when a RER=0.90 is reached in trained adults independently of sex, age, body weight status, or the Fatmax data analysis approach. In conclusion, we suggest reducing the RER from 1.0 to 0.95 to be sure that MFO is reached in outliers individuals. This methodological consideration has important clinical implications, since it would allow to apply smaller workload increments and/or to extend the stage duration to attain the steady-state, without increasing the test duration.

Keywords: MFO, FATmax, Peak fat oxidation, methodology, RER

Received: 10 Apr 2019; Accepted: 02 Jul 2019.

Edited by:

Gary Iwamoto, University of Illinois at Urbana-Champaign, United States

Reviewed by:

Todd A. Astorino, California State University San Marcos, United States
Nicholas A. Burd, University of Illinois at Urbana-Champaign, United States
Poghni A. Peri-Okonny, Saint Luke's Health System, United States  

Copyright: © 2019 Amaro-Gahete, Sanchez-Delgado, Helge and Ruiz. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mr. Francisco J. Amaro-Gahete, University of Granada, EFFECTS-262 Research group, Departament of Medical Physiology., Granada, Spain, amarof@ugr.es