Author(s): BERNABEU, A., HAYS, A., BENDAHAN, D., JUE, T., GIRAUD, D., BRÉGEON, F. , Institution: AIX-MARSEILLE UNIVERSITY, Country: FRANCE, Abstract-ID: 2345

INTRODUCTION:
It has been largely acknowledged that the vastus lateralis (VL) deoxygenation (HHb) measured by near-infrared spectroscopy (NIRS) during a maximal incremental test on an ergocycle typically displays a linear increase followed by a break point (BP) above the maximal aerobic capacity (MAP) [1,2]. However, the onset of BP varies substantially across individuals [1,3,4] while the corresponding physiological accounting factors remain poorly understood. In the present study, we aimed to better characterize the BP using a combined lactate, muscle (time-domain NIRS) and systemic oxygenation analysis. We hypothesized that different BP profiles could be distinguished based on this whole set of measurements.
METHODS:
13 trained male cyclists (19.7±0.9 years, V̇O₂max: 63.0±5.2 mL·min-1·kg-1) performed an incremental test to exhaustion (100 W + 25 W·2min-1). Both VL (time-domain NIRS) and systemic oxygenation (gas exchange analysis) were continuously monitored. First and second ventilatory thresholds (VT1, VT2) were determined using the Beaver method [5]. Capillary blood was sampled 2 min post-exercise to determine the maximal lactate concentration ([La]max). HHb kinetics were modelled using a double-linear regression resulting in 2 segments (S1, S2). BP intensity and slopes of S1 and S2 were determined. Statistical comparisons were performed using Mann-Whitney U tests.
RESULTS:
All subjects displayed a biphasic muscle oxygenation profile with 2 distinct patterns: 8 subjects (G1) displayed a deoxygenation acceleration (slope of S2 > slope of S1) after the BP whereas the remaining 5 subjects (G2) displayed a deoxygenation attenuation (slope of S2 < slope of S1). Of interest, BP occurred significantly earlier in G1 (70.08 ± 11.40 vs. 95.10 ± 9.20 % of MAP, p = 0.006). In addition, a higher power (300 ± 26.73 vs. 260 ± 13.69 W, p = 0.012) and a larger V̇O₂ (86.04 ± 2.53 vs. 80.93 ± 2.66 expressed %V̇O₂max, p = 0.016) at VT2 were quantified in G1. The MAP (350 ± 26.73 vs 300 ± 17.68 W, p = 0.007) was also larger. V̇O₂max (63.80 ± 6.16 vs. 60.52 ± 4.70 mL·min-1·kg-1, p = 0.21) and [La]max (10.32 ± 2.87 vs. 10.47 ± 1.83 mmol.L-1, p = 0.51) did not differ between groups.
CONCLUSION:
Combined muscle and systemic oxygenation measurements allow to distinguish two HHb patterns in the VL. The first profile was related to the occurrence of an early BP followed by an accelerated deoxygenation, while for the second profile, BP was delayed and followed by decelerated deoxygenation. The first profile was associated with a higher power output and V̇O₂ at VT2, as well as a larger MAP, despite similar V̇O₂max and [La]max between groups. These results suggest a potentially optimized peripheral efficiency in G1 which could be linked to a training effect. This inter-individual variability in peripheral O₂ extraction should be further documented in a larger amount of subjects.

References
[1] Boone & al., 2016 [2] Ianetta & al., 2017 [3] Ferreira & al., 2006 [4] Rupp & al., 2007 [5] Beaver & al., 1986