Frontiers in Physiology (Jun 2020)

Fat Oxidation Kinetics Is Related to Muscle Deoxygenation Kinetics During Exercise

  • Anouck Zurbuchen,
  • Stefano Lanzi,
  • Stefano Lanzi,
  • Ludovic Voirol,
  • Cybele Barboza Trindade,
  • Boris Gojanovic,
  • Bengt Kayser,
  • Nicolas Bourdillon,
  • Xavier Chenevière,
  • Davide Malatesta

DOI
https://doi.org/10.3389/fphys.2020.00571
Journal volume & issue
Vol. 11

Abstract

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PurposeThe present study aimed to determine whether whole-body fat oxidation and muscle deoxygenation kinetics parameters during exercise were related in individuals with different aerobic fitness levels.MethodsEleven cyclists [peak oxygen uptake (V.O2⁢p⁢e⁢a⁢k): 64.9 ± 3.9 mL⋅kg–1⋅min–1] and 11 active individuals (V.O2⁢p⁢e⁢a⁢k: 49.1 ± 7.4 mL⋅kg–1⋅min–1) performed a maximal incremental cycling test to determine V.O2⁢p⁢e⁢a⁢k and a submaximal incremental cycling test to assess whole-body fat oxidation using indirect calorimetry and muscle deoxygenation kinetics of the vastus lateralis (VL) using near-infrared spectroscopy (NIRS). A sinusoidal (SIN) model was used to characterize fat oxidation kinetics and to determine the intensity (Fatmax) eliciting maximal fat oxidation (MFO). The muscle deoxygenation response was fitted with a double linear model. The slope of the first parts of the kinetics (a1) and the breakpoint ([HHb]BP) were determined.ResultsMFO (p = 0.01) and absolute fat oxidation rates between 20 and 65% V.O2⁢p⁢e⁢a⁢k were higher in cyclists than in active participants (p < 0.05), while Fatmax occurred at a higher absolute exercise intensity (p = 0.01). a1 was lower in cyclists (p = 0.02) and [HHb]BP occurred at a higher absolute intensity (p < 0.001) than in active individuals. V.O2⁢p⁢e⁢a⁢k was strongly correlated with MFO, Fatmax, and [HHb]BP (r = 0.65–0.88, p ≤ 0.001). MFO and Fatmax were both correlated with [HHb]BP (r = 0.66, p = 0.01 and r = 0.68, p < 0.001, respectively) and tended to be negatively correlated with a1 (r = -0.41, p = 0.06 for both).ConclusionThis study showed that whole-body fat oxidation and muscle deoxygenation kinetics were both related to aerobic fitness and that a relationship between the two kinetics exists. Individuals with greater aerobic fitness may have a delayed reliance on glycolytic metabolism at higher exercise intensities because of a longer maintained balance between O2 delivery and consumption supporting higher fat oxidation rates.

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