Abstract
PURPOSE: Training above ventilatory threshold (VT), and corresponding heart rate, have resulted in improvements in aerobic capacity; the ability to oxidize fatty acids is a limiting factor in endurance performance. Additionally, little is known about the contribution of body composition on maximal fat oxidation (Fatmax). The purpose of this study was to characterize Fatmax and its relationship to VT in endurance trained young adult males. A secondary purpose was to understand the impact of body composition on Fatmax. METHODS: 25 trained males (Age: 22.2 ± 2.4 yrs; Height:177.0 ± 4.8 cm; Weight: 75.3 ± 6.9 kg; VO2max: 50.5 ± 14.6 mL/kg/min) were assessed for body composition using dual-energy X-ray absorptiometry to estimate lean mass (LM), fat mass (FM), and percent body fat (%BF). All subjects performed an incremental graded exercise test to volitional exhaustion. Fatmax was determined as the exercise intensity (%VO2max) at which the highest rate of fat oxidation was observed. VT was determined automatically from the software as the point by which respiration increased to compensate for CO2 and lactate accumulation. Paired t-tests were used to determine the differences between Fatmax and VT%VO2max, FatmaxVO2 and VTVO2, and HR at Fatmax and VT. Multiple linear regression was used to analyze the influence of body composition on Fatmax. RESULTS: There were no significant differences between Fatmax and VT%VO2 (Mean Difference ± Standard Error: -0.2 ± 0.1%; p = 0.107) or FatmaxVO2 and VTVO2 (-3.4 ± 3.1 L/min; p = 0.288). FatmaxHR was significantly lower than VTHR (-11.7 ± 3.1 bpm; p = 0.001). LM, FM, %BF did not significantly influence Fatmax (F = 0.888, R2 = 0.13, p = 0.464). CONCLUSIONS: The similar intensity observed between VT and Fatmax suggests training above VT could be a useful strategy for maximizing fat oxidation during exercise, thereby supporting glycogen sparing in addition to enhanced training volume and exercise adaptations. Body composition does not appear to be an important factor for Fatmax in young males.
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