The day-to-day reliability of peak fat oxidation and FATMAX
Oliver J. Chrzanowski‐Smith, Robert M. Edinburgh, Mark Thomas, Nicos Haralabidis, Sean Williams, James A. Betts, Javier T. Gonzalez
Abstract
Abstract Purpose Prior studies exploring the reliability of peak fat oxidation (PFO) and the intensity that elicits PFO (FAT MAX ) are often limited by small samples. This study characterised the reliability of PFO and FAT MAX in a large cohort of healthy men and women. Methods Ninety-nine adults [49 women; age: 35 (11) years; $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak: 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 FAT MAX (% $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak) by indirect calorimetry. Systematic bias and the absolute and relative reliability of PFO and FAT MAX 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 FAT MAX was found between exercise tests in the entire sample (− 0.01 g·min −1 and 0% $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak, 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% $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak; 95% limits of agreement: ± 0.17 g·min −1 and × / ÷ 1.90% $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2 peak, respectively), despite high ( r = 0.75) and moderate ( r = 0.45) relative reliability for PFO and FAT MAX, respectively. These findings were consistent across all sub-groups. Conclusion Repeated assessments are required to more accurately determine PFO and FAT MAX .