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

Oliver Chrzanowski-Smith, Rob Edinburgh, Mark Thomas, Nicos Haralabidis, Sean Williams, James Betts, Javier Gonzalez

Research output: Contribution to journalArticlepeer-review

19 Citations (SciVal)


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; V˙ O 2peak: 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 (%V˙ O 2peak) 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%V˙ O 2peak, 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%V˙ O 2peak; 95% limits of agreement: ± 0.17 g·min −1 and × / ÷ 1.90%V˙ O 2peak, 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.

Original languageEnglish
Pages (from-to)1745-1759
Number of pages15
JournalEuropean Journal of Applied Physiology
Issue number8
Publication statusPublished - 15 Jun 2020


  • Exercise metabolism
  • FAT
  • Indirect calorimetry
  • Peak fat oxidation
  • Reliability
  • Variation

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine
  • Public Health, Environmental and Occupational Health
  • Physiology (medical)


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