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Clinical Trial
. 2020 Aug;120(8):1745-1759.
doi: 10.1007/s00421-020-04397-3. Epub 2020 Jun 1.

The day-to-day reliability of peak fat oxidation and FATMAX

Oliver J Chrzanowski-Smith  1 , Robert M Edinburgh  1 , Mark P Thomas  1 , Nicos Haralabidis  1 , Sean Williams  1 , James A Betts  1 , Javier T Gonzalez  2
Affiliations
Clinical Trial

The day-to-day reliability of peak fat oxidation and FATMAX

Oliver J Chrzanowski-Smith et al. Eur J Appl Physiol. 2020 Aug.

Abstract

Purpose: Prior studies exploring the reliability of peak fat oxidation (PFO) and the intensity that elicits PFO (FATMAX) are often limited by small samples. This study characterised the reliability of PFO and FATMAX in a large cohort of healthy men and women.

Methods: Ninety-nine adults [49 women; age: 35 (11) years; [Formula: see text]O2peak: 42.2 (10.3) mL·kg BM-1·min-1; mean (SD)] completed two identical exercise tests (7-28 days apart) to determine PFO (g·min-1) and FATMAX (%[Formula: see text]O2peak) by indirect calorimetry. Systematic bias and the absolute and relative reliability of PFO and FATMAX were explored in the whole sample and sub-categories of: cardiorespiratory fitness, biological sex, objectively measured physical activity levels, fat mass index (derived by dual-energy X-ray absorptiometry) and menstrual cycle status.

Results: No systematic bias in PFO or FATMAX was found between exercise tests in the entire sample (- 0.01 g·min-1 and 0%[Formula: see text]O2peak, respectively; p > 0.05). Absolute reliability was poor [within-subject coefficient of variation: 21% and 26%; typical errors: ± 0.06 g·min-1 and × / ÷ 1.26%[Formula: see text]O2peak; 95% limits of agreement: ± 0.17 g·min-1 and × / ÷ 1.90%[Formula: see text]O2peak, respectively), despite high (r = 0.75) and moderate (r = 0.45) relative reliability for PFO and FATMAX, respectively. These findings were consistent across all sub-groups.

Conclusion: Repeated assessments are required to more accurately determine PFO and FATMAX.

Keywords: Exercise metabolism; FATMAX; Indirect calorimetry; Peak fat oxidation; Reliability; Variation.

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Conflict of interest statement

The authors declare no conflicts of interest. JTG has received research funding and has acted as a consultant for Arla Foods Ingredients, Lucozade Ribena Suntory, Kenniscentrum Suiker and Voeding, and PepsiCo. JAB has received research funding and has acted as a consultant for GlaxoSmithKline, Lucozade Ribena Suntory, Kellogg’s, Nestlé, and PepsiCo.

Figures

Fig. 1
Fig. 1
Comparison of Trial A and Trial B for peak fat oxidation rate (a; g·min−1) and FATMAX (b %V˙O2peak) in all participants (whole sample). The solid thick line represents mean ± SD (or × / ÷ for FATMAX) with individual data denoted by the thin lines (dashed = Females; solid = Males). c A Bland–Altman plot displaying the difference in PFO (g·min−1) between Trial A and B. The solid line represents bias and the dashed lines represent lower and upper 95% limits of agreement. Females are denoted by open circles and males are indicated by filled circles. Measured values approach used to determine PFO and FATMAX
Fig. 2
Fig. 2
Comparison of peak fat oxidation (g·min−1; a) and FATMAX (%V˙O2peak; b) between the different data analysis approaches applied to determine PFO and FATMAX (values reflect an average of Trial A and Trial B). The solid thick line represents mean ± SD with individual data denoted by the thin lines
See this image and copyright information in PMC

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