Applications of near-infrared spectroscopy in “anaerobic” diagnostics – SmO(2) 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 SmO(2)(t), phosphagen energy supply W(PCr)(t) and blood lactate accumulation ΔBLC(t) during a 60-s all-out cycling sprint and tested SmO(2)(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. SmO(2) of the vastus lateralis muscle and respiratory gases were measured until the 30(th) 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 SmO(2), 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 (R(2) > 0.95). The time constant of SmO(2)(t) τ(SmO2) = 2.93 ± 0.65 s was correlated with the time constant of W(PCr)(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 SmO(2) 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 SmO(2) desaturation indicates the end of the fatigue-free state.