Objectives The substrates utilisation at high intensity exercise has been less studied and intensity at which carbohydrates (CHO) remain single energy source while fat utilisation becomes negligible (FATmin), is debatable 4. Since physical activity in aerobic fat burn zone is prescribed to facilitate improvement of fat oxidation and insulin sensitivity while improving health 1, activity equal or above FATmin can’t be considered as beneficial. Therefore, FATmin could become important exercise parameter in sedentary population. The aim of this study was to determine FATmin while performing incremental treadmill test till exhaustion and to assess its correlation with anaerobic threshold (AT), which in turn can be used as an individuals performance marker or last exercise beneficial point.
Methodology Thirteen sedentary females (age: 34 ± 3 y, body mass: 62 ± 4 kg, height: 165 ± 4 cm) performed breath-by-breath test to measure maximal oxygen uptake (VO2max;ml·kg-1·min-1) and substrates oxidation (g·min-1). A Pearson correlation coefficient (r), 95% confidence interval (CI) and effect size (R2 ) were used to test connexion between VO2 at AT and at FATmin. Alpha intervals were set at p < 0.05. Substrates oxidation was calculated using a stoichiometric equation 4. The AT was detected by V-slope method 2.
Results VO2max was 34.89 ± 4.34 ml·kg-1·min-1 (95% CI 34.02 to 35.52). FATmin and AT occurred at 24.53 ± 4.25 ml·kg-1·min-1 VO2 (95% CI 24.29 to 24.97) and 24.04 ± 4.07 ml·kg-1·min-1 VO2 (95% CI 24.01 to 24.80), respectively. A high correlation was found between VO2 at FATmin and at AT (r = 0.91, p < 0.001, 95 % CI of 0.87 to 0.93). R2 was 0.83. Absolute fat oxidation rate at FATmin was 0.01 ± 0.01 g·min-1 (95% CI 0.00 to 0.01).
Conclusions This is the first study to detect FATmin and demonstrate correlation between VO2 at FATmin and at AT in sedentary females. High inter-subjects FATmin variation demonstrates marked degree of individuality and importance of existing correlation should be taken into consideration when aiming to optimise exercise prescription for sedentary population.
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Peric R, Meucci M, Nikolovski Z. Fat utilisationutilization during high intensity exercise: when does it end? Sport Med Open 2016;2(35). DOI: 10.1186/s40798-016-0060-1
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