Validation of muscle oxygenation kinetics to predict aerobic fitness and exercise transition thresholds

The aim of this study was to validate previously developed equations to predict maximal oxygen uptake ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> ) from near-infrared spectroscopy (NIRS) during and after a period of limb ischaemia. Moreover, NIRS recovery kinetics after steady-state exercise (SSE) could be used to monitor <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> and exercise intensity thresholds. Seventeen healthy adults completed a 3 min 300 mmHg pressure cuff occlusion to measure the occlusion slope, relative rate of muscle reoxygenation at 10 s (Rep 10s), baseline (R_bl), peak (R_peak) and area under the curve (AUC_2min). SSE was performed at 100 W (SSE1) and 150 W (SSE2) to determine the relative rate of muscle reoxygenation (R1_bl and R2_bl). Thereafter, incremental maximal cycling was used to determine <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> , ventilatory thresholds (VTs) and gross efficiencies (GEs). The values of Rep 10s (r = 0.61, p = 0.02), R_bl (r = 0.53, p = 0.04), R_peak (r = 0.60, p = 0.02), AUC_2min (r = 0.67, p < 0.01) and occlusion slope (r = -0.68, p = 0.005) were correlated with absolute <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> . After steady-state cycling, SSE1 R_bl was correlated with absolute <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> (r = 0.67, p = 0.01) and relative <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> (r = 0.60, p = 0.02), in addition to absolute VT1 (r = 0.66, p = 0.01) and relative VT1 (r = 0.61 p = 0.02). The SSE2 R_bl was correlated with absolute <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> (r = 0.58, p = 0.02), relative <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> (r = 0.63, p = 0.02), absolute VT2 (r = 0.56, p = 0.03), relative VT2 (r = 0.62, p = 0.01) and GE2 (r = 0.56, p = 0.03). Using previously defined prediction equations, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> could be predicted with a modest degree of typical error (Rep 10s, 521 mL min^-1; R_peak, 525 mL min^-1; slope, 393 mL min^-1). NIRS kinetic profiles during or after a period of ischaemia or after SSE are related to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_{\mathrm{2}}}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> and exercise intensity thresholds. Nonetheless, their predictive validity is limited to a broad estimate of the aerobic fitness of an individual.