Cycling exercise transitions showed an initial unmodified muscle oxygenation time delay of 8.9s below and 6.4s above the ventilatory threshold, indicating adequate O2 availability.
Observational (n=10)
Near-infrared spectroscopy (NIRS) was utilized to gain insights into the kinetics of oxidative metabolism during exercise transitions. Ten untrained young men were tested on a cycle ergometer during transitions from unloaded pedaling to 5 min of constant-load exercise below (VT) the ventilatory threshold. Vastus lateralis oxygenation was determined by NIRS, and pulmonary O2 uptake (Vo --> Vo2) was determined breath-by-breath. Changes in deoxygenated hemoglobin + myoglobin concentration Deltadeoxy(Hb + Mb) were taken as a muscle oxygenation index. At the transition, Delta[deoxy(Hb + Mb)] was unmodified time delay (TD) for 8.9 +/- 0.5 s at VT (both significantly different from 0) and then increased, following a monoexponential function time constant (tau) = 8.5 +/- 0.9 s for VT. For >VT a slow component of Deltadeoxy(Hb + Mb) on-kinetics was observed in 9 of 10 subjects after 75.0 +/- 14.0 s of exercise. A significant correlation was described between the mean response time (MRT = TD + tau) of the primary component of Deltadeoxy(Hb + Mb) on-kinetics and the tau of the primary component of the pulmonary Vo2 on-kinetics. The constant muscle oxygenation during the initial phase of the on-transition indicates a tight coupling between increases in O2 delivery and O2 utilization. The lack of a drop in muscle oxygenation at the transition suggests adequacy of O2 availability in relation to needs.
Grassi et al. (Tue,) conducted a observational in Healthy untrained (n=10). Cycling exercise transitions vs. Below vs above ventilatory threshold (<VT vs >VT) was evaluated on Muscle oxygenation index (changes in deoxygenated hemoglobin + myoglobin concentration) and pulmonary O2 uptake kinetics. Cycling exercise transitions showed an initial unmodified muscle oxygenation time delay of 8.9s below and 6.4s above the ventilatory threshold, indicating adequate O2 availability.