Purpose: The aim of the present study was to investigate whether the sigmoid pattern of deoxy[Hb + Mb] during incremental exercise is specific to non-steady-state conditions.
Methods: Ten highly trained cyclists performed an incremental step (40 W·3 min−1) and ramp (35 W·min−1) exercise. Deoxy[Hb + Mb] was measured at the distal and proximal sites of the musculus vastus lateralis throughout the exercises using near-infrared spectroscopy. Deoxy[Hb + Mb] was set out as a function of work rate (% peak power), and using curve-fitting techniques, the best-fitting model was determined.
Results: These procedures showed that the sigmoid pattern also provided the best fit for the pattern of deoxy[Hb + Mb] in the step exercise. Furthermore, it was observed that the sigmoid model was similar for the ramp (d = 6.9% ± 1.1% and 6.9% ± 1.4%·%−1 peak power; c/d = 52.1% ± 3.8% and 52.1% ± 4.5% peak power, for the proximal and distal measurement sites, respectively) and the step exercise (d = 7.4% ± 1.5% and 6.4% ± 1.5%·%−1 peak power; c/d = 52.3% ± 6.0% and 52.5% ± 4.2% peak power, for the proximal and distal measurement sites, respectively). The pattern of deoxy[Hb + Mb] was not influenced by measurement site.
Conclusions: From the present study, it can be concluded that the sigmoid pattern of deoxy[Hb + Mb] during incremental exercise is not specific to non-steady-state conditions. It was hypothesized that this pattern is an expression of a nonlinear Q˙m/V˙O2m relationship, related to changes in muscle fiber-type recruitment.