Author(s): QUITTMANN, O.J., VAN EIK, S., ABEL, T., Institution: GERMAN SPORT UNIVERSITY COLOGNE, Country: GERMANY, Abstract-ID: 851

INTRODUCTION:
Maximal fat oxidation (MFO) has implications for metabolic health [1] and explains between 12-14% of the variance in ultra-endurance events [2,3]. MFO seems to be influenced by training status, exercise intensity/duration, nutrition and sex [4]. Regarding the latter, there are still inconclusive findings on the influence of sex, that are biased by the expressed units and performance differences between groups [5,6]. This study aimed to compare MFO and the corresponding intensity (Fatmax) between females and males who are matched for maximal oxygen uptake (V̇O2max).
METHODS:
A sub-sample was taken from a previous study in N = 44 well-trained runners/triathletes [7]. Ultimately, n = 10 females and n = 10 males met the inclusion criterion of a V̇O2max between 55 and 63 ml/min/kg. Substrate oxidation rates were calculated from a graded exercise test by using equations of stoichiometry [8]. Fat oxidation was calculated for every intensity level and interpolated by a quadratic polynomial to determine MFO and Fatmax (expressed in %V̇O2max). Normality was checked by the Kolomogorov-Smirnov test (α=10%). Based on this criterion, comparisons between groups were performed by an independent t-test or the Mann-Whitney-U-test (α=5%). Effect-sizes were calculated as Cohen’s d.
RESULTS:
There was no significant difference between females and males in terms of V̇O2max (d=-0.331, p=0.533), MFO (d=-0.500, p=0.269), Fatmax (d=0.030, p=0.948), onset of blood lactate accumulation (d=-0.775, p=0.108) and maximal lactate accumulation rate (d=-0.919, p=0.600). MFO was 0.38±0.14 and 0.45±0.14 g/min in females and males, respectively. Even if MFO was normalised to fat free mass, there was no difference between sexes (d=0.330, p=0.432). However, females needed significantly more time to cover a 5-km time trial (d=1.383, p=0.006).
CONCLUSION:
MFO and Fatmax were similar in females and males who are matched for V̇O2max. This indicates that the influence of training status is higher than the influence of sex per se. However, these results are specific for the applied protocol, equipment and equations, that seem to influence outcomes of fat oxidation [9]. Limitations worth mentioning are that no concrete standardizations were applied in terms of nutrition, daytime and menstrual cycle between participants, which increases the secondary variance of this study. Future studies should validate these findings in a larger and more standardized sample as well as in elite (endurance) athletes.

References
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7) Quittmann et al. (2022) Int J Sports Med
8) Péronnet & Massicotte (1991) Can J Sport Sci
9) Amaro-Gahete et al. (2019) Scand J Med Sci Sports