Reproducibility of Fatmax and Fat Oxidation Rates during Exercise in Recreationally Trained Males

Abstract

Aerobic exercise training performed at the intensity eliciting maximal fat oxidation (Fatmax) has been shown to improve the metabolic profile of obese patients. However, limited information is available on the reproducibility of Fatmax and related physiological measures. The aim of this study was to assess the intra-individual variability of: a) Fatmax measurements determined using three different data analysis approaches and b) fat and carbohydrate oxidation rates at rest and at each stage of an individualized graded test. Fifteen healthy males [body mass index 23.1±0.6 kg/m2, maximal oxygen consumption () 52.0±2.0 ml/kg/min] completed a maximal test and two identical submaximal incremental tests on ergocycle (30-min rest followed by 5-min stages with increments of 7.5% of the maximal power output). Fat and carbohydrate oxidation rates were determined using indirect calorimetry. Fatmax was determined with three approaches: the sine model (SIN), measured values (MV) and 3rd polynomial curve (P3). Intra-individual coefficients of variation (CVs) and limits of agreement were calculated. CV for Fatmax determined with SIN was 16.4% and tended to be lower than with P3 and MV (18.6% and 20.8%, respectively). Limits of agreement for Fatmax were −2±27% of with SIN, −4±32 with P3 and −4±28 with MV. CVs of oxygen uptake, carbon dioxide production and respiratory exchange rate were <10% at rest and <5% during exercise. Conversely, CVs of fat oxidation rates (20% at rest and 24–49% during exercise) and carbohydrate oxidation rates (33.5% at rest, 8.5–12.9% during exercise) were higher. The intra-individual variability of Fatmax and fat oxidation rates was high (CV>15%), regardless of the data analysis approach employed. Further research on the determinants of the variability of Fatmax and fat oxidation rates is required.

Reliability and Day-to-day Variability of Peak Fat Oxidation During Treadmill Ergometry

“…However, whilst these results enable closer comparisons to some of those from other investigations, making reasonable inferences as to the physiological plausibility and practical applicability of these LoA has shown to be a challenging task. As implied by Croci [16], previous studies have deemed an intra-individual variability of ± 10 beats/min for HR at V PFO as acceptable, since this reflects a realistic margin in individuals who use HR for the monitoring of training intensity [7,15]. Accordingly, in the present investigation this threshold has been sustained in most participants, with only three of them eventually exceeding the given cutoff (though by no more than 3 beats/min).…”

“…To date, there have been a few investigations assessing the reproducibility of Fat peak [6,7,[13][14][15][16]. Though the majority of those have failed to make thorough statistical analyses by not providing indicators of both relative and absolute reliability for Fat peak estimations (i.e.…”

“…The reproducibility of the intensity eliciting peak fat oxidation (PFO) rates (i.e. Fat peak , but also referred to as Fat max or LIPOXmax) has been reported for a variety of submaximal incremental protocols [6,7,[13][14][15][16]. However, all reliability studies to date have used cycle ergometry as the exercising method of choice, which in turn may limit a valid transferability from any of the previously tested protocols and their respective reproducibility indicators into other types of exercise.…”

Assessment of maximal fat oxidation during exercise: A systematic review

“…The data analysis approaches used across the studies included were the following: (a) The measured‐values data analysis approach was applied in 37 studies (33.0%). This data analysis approach is based on the highest fat oxidation rate recorded in the graded exercise protocol . (b) 25 studies applied the 2nd polynomial curve data analysis approach, and nine studies applied the 3rd polynomial data analysis approach (22.3% and 8.0%, respectively).…”

“…This data analysis approach is based on the graphical depiction of fat oxidation as a function of exercise intensity performing a 2nd or 3rd polynomial curve with intersection at (0;0). Fat max can be calculated by differentiation of the 2nd or 3rd polynomial equation and corresponded to the intensity at which the value of the differentiated equation was equal to zero . (c) The sine model data analysis approach was used in nine studies (7.1%).…”