Reliability of the Metabolic Response During Steady-State Exercise at FATmax in Young Men with Obesity

ABSTRACT

Purpose: In this study we evaluated the reliability of blood lactate levels (BLa), energy expenditure and substrate utilization during prolonged exercise at the intensity that elicits maximal fat oxidation (FATmax). Furthermore, we investigated the accuracy of a single graded exercise test (GXT) for predicting energy metabolism at FATmax. Methods: Seventeen young men with obesity (26 ± 6 years; 36.4 ± 7.2 %body fat) performed a GXT on a treadmill in a fasted state (10–12 h) for the assessment of FATmax and cardiorespiratory fitness. Afterward, each subject performed two additional prolonged FATmax trials (102 ± 11 beats·min⁻¹; 60-min) separated by 7 days. Indirect calorimetry was used for the assessment of energy expenditure and substrate utilization kinetics whereas capillary blood samples were taken for the measurement of BLa. Results: The BLa (limits of agreement (LoA): −1.2 to 0.8 mmol∙L⁻¹; p = 1.0), fat utilization (LoA: −8.0 to 13.4 g∙h⁻¹; p = 0.06), and carbohydrate utilization (LoA: −27.6 to 22.4 g∙h⁻¹; p = 0.41) showed a good agreement whereas a modest systematic bias was found for energy expenditure (LoA: −16811 to 33355 kJ∙h⁻¹; p < 0.05). All the aforementioned parameters showed a moderate to good reliability (Intraclass correlation coefficient: 0.67–0.92). The GXT overestimated fat (~46%) and carbohydrate (~26%) utilization as well as energy expenditure (36%) during steady-state exercise at FATmax. Conversely the GXT underestimated BLa (~28%). Conclusion: a single GXT cannot be used for an accurate prediction of energy metabolism during prolonged exercise in men with obesity. Thus, an additional steady-state FATmax trial (40–60 min) should be performed for a tailored and precise exercise prescription.

KEYWORDS:

• Energy metabolism
• exercise test
• indirect calorimetry
• nutrition
• physical exercise

Acknowledgments

The authors would like to thank all the subjects who kindly participated in this study. Likewise, the authors recognize Dr. Marina Trejo who donated the test strips for the analysis of blood lactate levels. IACG was supported by a Ph.D scholarship (859438) from the Consejo Nacional de Humanidades, Ciencia y Tecnología (Conahcyt). However, the institution did not participate in the study design or manuscript preparation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contribution statement

Investigation, I.A.C.-G.; conceptualization and methodology, A.R.-J. and I.A.C-G.; formal analysis, F.J.A.-G., I.A.C-G., R.P.; data curation, R.P. and F.J.A.-G; writing—original, I.A.C.-G.; writing—review and editing, A.R.-J., F.J.A.-G and R.P.; visualization, F.J.A.-G. and I.A.C.-G; supervision and project administration, A.R.-J. All authors have read and agreed to the published version of the manuscript.

Data availability statement

The dataset supporting the findings from this study is available from the lead author upon reasonable request.

IRB approval

The study protocol was reviewed and approved by the Ethics Committee of the Autonomous University of Ciudad Juarez (CIBE-2018-1-11) prior study initiation.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02701367.2024.2311641.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.