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The Agreement between Fat max and the Gas-Exchange and Blood Lactate Thresholds: A Systematic Review and
Clorinda Hogan1, Troy J Cross1,2, Megan Tiong1,2
1Discipline of Exercise and Sport Science, Faculty of Medicine and Health, The University of Sydney, Camperdown, NSW, AUSTRALIA.
Background:
The relationship between the exercise intensity at which maximal fat oxidation occurs (Fat max ) and the lactate threshold/gas-exchange threshold (LT/GET) has gained interest in both sport performance and health-related communities, yet the absolute agreement between these two "thresholds" remains inconsistent. This review aims to systematically assess the available literature to determine whether Fat max occurs at the same exercise intensity as the LT/GET and to examine whether aspects of study design moderated this relationship.
Methods:
PubMed, MEDLINE, Embase, and Scopus were systematically searched from inception to January 20, 2025. Studies were included if they reported Fat max and measures of the LT/GET in healthy adults. Exercise intensities corresponding to these thresholds were analyzed using a random-effects multilevel meta-analysis. Univariate moderator analyses were performed to identify potential methodological or participant-related moderators of the effect size.
Results:
The meta-analysis ( N = 42 studies) revealed that Fat max occurred at a significantly lower exercise intensity than LT/GET, by approximately 5.78% , 4.75 mL·min -1 ·kg -1 , 22 W, or 11 beats ·min -1 (effect size = 0.74, 95% confidence interval = 0.32-1.16, P = 0.001). Moderator analyses indicated that differences between Fat max and LT/GET varied according to participant characteristics (e.g., age, sex, and fitness level), nutritional status, study design, testing protocols, and analytical methods.
Conclusions:
Although Fat max typically occurs at a lower exercise intensity than the LT/GET, this difference appears smaller in sedentary individuals (<20 yr), when testing is performed with a <6-h fasting period, and when treadmill-based, two separate sessions protocols are employed. Under these conditions, the LT/GET could serve as a surrogate for Fat max when direct substrate oxidation measurement is not feasible.
