Pattern of deoxy[Hb + Mb] during ramp cycle exercise: influence of aerobic fitness status

During ramp exercise the deoxy[Hb + Mb] pattern follows a sigmoid model [f(x) = f ₀ + A/(1 + exp^{−(−c  + dx)})], indicating a non-linear muscle blood flow \( (\dot{Q}{\text{m}})/{\text{oxygen}}\;{\text{uptake}}\;(\dot{V}{\text{O}}_{{2{\text{m}}}} ) \)-relationship. We hypothesised that in trained cyclists the sigmoid would display a rightward shift, due to an increased oxidative capacity and/or higher percentage of slow-twitch fibres. A total of 10 cyclists and 11 physically active students (PA students) performed a relative ramp exercise (±12 min) and a ramp25-exercise (25 W min⁻¹). Deoxy[Hb + Mb] was measured at the M. Vastus Lateralis by NIRS, normalized to the total amplitude of the response and expressed as a function of absolute and relative (%peakP) work rate. The work rate corresponding to c/d (i.e.50% of the amplitude of the deoxy[Hb + Mb] response) was the only parameter of the sigmoid that differed significantly between cyclists (57.9 ± 4.4% and 60.1 ± 4.1%peakP in the relative and ramp25, respectively) and PAstudents (49.6 ± 4.2% and 48.2 ± 5.1%peakP, respectively), indicating a rightward shift of the sigmoid in the cyclists. These results suggest a change in the time course of C_(a–v)O₂ as a function of aerobic fitness status.