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 ( ${\dot{V}}_{O_2\max }$ ) 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 ${\dot{V}}_{O_2\max }$ 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 ${\dot{V}}_{O_2\max }$ , 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 ${\dot{V}}_{O_2\max }$ . After steady-state cycling, SSE1 R_bl was correlated with absolute ${\dot{V}}_{O_2\max }$ (r = 0.67, p = 0.01) and relative ${\dot{V}}_{O_2\max }$ (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 ${\dot{V}}_{O_2\max }$ (r = 0.58, p = 0.02), relative ${\dot{V}}_{O_2\max }$ (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, ${\dot{V}}_{O_2\max }$ 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 ${\dot{V}}_{O_2\max }$ and exercise intensity thresholds. Nonetheless, their predictive validity is limited to a broad estimate of the aerobic fitness of an individual.