Applications of near-infrared spectroscopy in “anaerobic” diagnostics – SmO₂ kinetics reflect PCr dephosphorylation and correlate with maximal lactate accumulation and maximal pedalling rate

We investigated the relationship of the time-dependent behaviour of muscle oxygen saturation SmO₂(t), phosphagen energy supply W_PCr(t) and blood lactate accumulation ΔBLC(t) during a 60-s all-out cycling sprint and tested SmO₂(t) for correlations with the end of the fatigue-free state t_Ff, maximal pedalling rate PR_max and maximal blood lactate accumulation rate v̇La_max. Nine male elite track cyclists performed four maximal sprints (3, 8, 12, 60 s) on a cycle ergometer. Crank force and cadence were monitored continuously to determine PR_max and t_Ff based on force-velocity profiles. SmO₂ of the vastus lateralis muscle and respiratory gases were measured until the 30th minute after exercise. W_PCr was calculated based on the fast component of the post-exercise oxygen uptake for each sprint. Before and for 30 minutes after each sprint, capillary blood samples were taken to determine the associated ΔBLC. Temporal changes of SmO₂, W_PCr and ΔBLC were analysed via non-linear regression analysis. v̇La_max was calculated based on ΔBLC(t) as the highest blood lactate accumulation rate. All models showed excellent quality (R² > 0.95). The time constant of SmO₂(t) τSmO₂ = 2.93±0.65 s was correlated with the time constant of WPCr(t) τ_PCr = 3.23±0.67 s (r = 0.790, p < 0.012), v̇La_max = 0.95±0.18 mmol·l⁻¹ ·s⁻¹(r = 0.768, p < 0.017) and PR_max = 299.51±14.70 rpm (r = -0.670, p < 0.049). t_Ff was correlated with τ_SmO2 (r = 0.885, p < 0.001). Our results show a time-dependent reflection of SmO₂ kinetics and phosphagen energy contribution during a 60-s maximal cycling sprint. A high v̇La_max results in a reduction, a high PR_max in an increase of the desaturation rate. The half-life of SmO₂ desaturation indicates the end of the fatigue-free state.