The Agreement between Fat max and the Gas-Exchange and Blood Lactate Thresholds: A Systematic Review and...

Area of Science:

• Exercise Physiology
• Metabolic Adaptations
• Sports Science

Background:

• The relationship between maximal fat oxidation intensity (Fatmax) and exercise thresholds like lactate threshold/gas-exchange threshold (LT/GET) is of interest in sports performance and health.
• Existing literature shows inconsistent agreement between Fatmax and LT/GET intensities.
• This review systematically assesses the literature to clarify the relationship and identify moderating factors.

Purpose of the Study:

• To systematically review and meta-analyze studies comparing exercise intensity at Fatmax versus LT/GET.
• To determine if Fatmax occurs at the same intensity as LT/GET.
• To investigate how study design and participant characteristics moderate the relationship between Fatmax and LT/GET.

Main Methods:

• A systematic literature search was conducted across PubMed, MEDLINE, Embase, and Scopus databases.
• Studies reporting both Fatmax and LT/GET in healthy adults were included.
• A random effects multilevel meta-analysis and univariate moderator analyses were performed.

Main Results:

• The meta-analysis of 42 studies found Fatmax occurred at a significantly lower exercise intensity than LT/GET (approx. 5.78% V̇O2max lower).
• Differences varied based on participant characteristics (age, sex, fitness), nutritional status, and study protocols.
• Moderator analyses identified key factors influencing the Fatmax-LT/GET relationship.

Conclusions:

• Fatmax generally occurs at a lower exercise intensity than LT/GET.
• The difference is smaller in sedentary individuals (<20 years), with shorter fasting periods (<6 hours), and using treadmill-based, two-session protocols.
• Under these specific conditions, LT/GET may serve as a practical surrogate for Fatmax when direct measurement is not feasible.