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 (SmO₂) 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. SmO₂ 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 SmO₂ kinetics and vLa_max were observed: (1) a very strong inverse relationship (r = -0.994, p < 0.001) between SmO₂ desaturation and vLa_max time dependent kinetics, (2) a significant inverse relationship (r = -0.648, p < 0.001) between SmO₂ 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 SmO₂ 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. SmO₂ desaturation closely reflects the vLa_max kinetics, with the time points of the SmO₂ nadir and peak vLa_max closely corresponding.