Applications of near-infrared spectroscopy in “anaerobic” diagnostics – SmO 2 kinetics reflect PCr dephosphorylationand correlate with maximal lactate accumulation and maximal pedalling rate

Figures

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  FIG. 1. Example of the time-course of power output P (W), oxygen consumption V̇O2 (l · min−1), and blood lactate concentration BLC (mmol · l−1) during the 60-s cycling sprint test protocol.

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  FIG. 2. Mean model function of EPOC(t) after the 60-s sprint test with its fast (V̇O2FC) and slow components (V̇O2SC) and the asymptotic resting level of oxygen uptake (V̇O2Base). The fast component corresponds to the amount of energy gained from the dephosphorylation of high-energy phosphates during exercise.

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  FIG. 3. A typical example of the data for the total mass of haemoglobin and myoglobin (tHb) with its oxygenated portion (oxHb) and for the muscle oxygen saturation data (SmO2) with the calculated model SmO2(t) during the 60-s sprint test. SmO2(t) showed a very good description of the SmO2 raw data until the middle of the test. After that, a slight increase in SmO2 could be observed despite the athlete’s maximal effort. The level of tHb was almost constant throughout the sprint. This phenomenon could be observed in all athletes.

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  FIG. 4. Mean time-dependent O2 saturation of the vastus lateralis muscle (SmO2(t)), mean time-dependent blood lactate accumulation (ΔBLC(t)) and mean time-dependent phosphagen energy supply (WPCr(t)) during the 60-s sprint test. By visual comparison, a high correlation of the kinetics can be assumed, which could be confirmed statistically.

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  FIG. 5. Results of the correlation analysis between the time constant of SmO2(t)(τSmO2) and A) the time constant of WPCr(t) (τPCr), B) the maximal rate of blood lactate accumulation (v̇Lamax), C) the maximal pedalling rate (PRmax) and D) the end of the fatigue-free state (tFf).

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  FIG. 6. Deviation of the model of the time-dependent amount of alactic energy predicted using the mean time constant of SmO2(t) from the mean original model of WPCr(t) in each second during the 60-s sprint with bias and standard deviation (SD).

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  FIG. 7. Visualisation of the mean time courses of oxygen saturation SmO2(t) [%], time-dependent anaerobic alactic energy contribution WPCr(t) [kJ], time-dependent blood lactate accumulation ΔBLC(t) [mmol · l−1] and resulting lactate formation rate v̇La(t) [mmol · l−1 · s−1] with suggested interpretation of characteristic point in times: At the onset of maximal exercise the rate of PCr split reflects the energy demand of the working muscle [16, 17]. About the have of the PCr stored in the muscle can be depleted without significant changes in ATP depletion rate and ATP concentration in the working muscle [16]. Assuming that glycolytic and oxidative ATP resynthesis is activated by the cell’s ADP concentration or phosphorylation deficit, a subsequent rapid increase in ADP or Cr will then activate glycolytic and mitochondrial ATP resynthesis to compensate for an increased rate of dephosphorylation [12]. The higher the rate of glycolytic and mitochondrial rephosphorylation, the slower the rate of PCr dephosphorylation subsequently. Due to the comparatively low glycolytic and the even lower oxidative ATP resynthesis rate – especially at the beginning of maximal exercise – the energy flow in the…