The relationship between muscle oxygen saturation kinetics and maximal blood lactate accumulation rate across varying sprint cycle durations

This study evaluated the relationship between muscle oxygen saturation (SmO 2) and the maximal blood lactate accumulation rate (vLa max) during three test durations (10, 15 and 30 s) to validate the optimal test duration of vLa max protocol. Thirteen developmental trained males (age: 27 ± 6 years and peak power: 1133 ± 185W and 14.88 ± 1.61 W·kg -1) performed three maximal cycle tests (10, 15 and 30 s). Performance metrics were measured throughout; peak power, mean power, and cadence. vLa max was determined using blood lactate concentrations following each test. SmO 2 of the vastus lateralis was measured using a MOXY device via near-infrared spectroscopy, throughout all experimental conditions. The shortest test (10 s) produced a significantly (p = 0.005; p < 0.001) higher vLa max (0.83 ± 0.15 mmol·L -1·s -1) than 15 s (0.67 ± 0.13 mmol·L -1·s -1) and 30 s (0.43 ± 0.06 mmol·L -1·s -1). Three relationships between SmO 2 kinetics and vLa max were observed: (1) a very strong inverse relationship (r = -0.994, p < 0.001) between SmO 2 desaturation and vLa max time dependent kinetics, (2) a significant inverse relationship (r = -0.648, p < 0.001) between SmO 2 time spent at the nadir and vLa max and (3) a moderate relationship (r = 0.508, p = 0.11) and similar time to attain the SmO 2 nadir (8.47 ± 1.50s) and vLa max (8.92 ± 0.77s). These results validate the 10-s test duration for determination of vLa max verified with mathematical modelling predicting peak vLa max occurs at ∼9 s. SmO 2 desaturation closely reflects the vLa max kinetics, with the time points of the SmO 2 nadir and peak vLa max closely corresponding.