Abstract
The purpose of this study was to characterize cerebrovascular responses to rowing exercise, investigating whether their diurnal variation might explain performance differences across a day. Twelve male rowers completed incremental rowing exercise and a 2000-m ergometer time trial at 07:00h and 16:00h, 1 week apart, while middle cerebral artery velocity (MCAv), cerebral (prefrontal), and muscular (vastus lateralis) tissue oxygenation and hemoglobin volume (via near-infrared spectroscopy), heart rate, and pressure of end-tidal CO2 (PETCO2) were recorded. MCAv was 20-25% above resting levels (68 +/- 12cm/s) during submaximal and maximal exercise intensities, despite PETCO2 being reduced during maximal efforts (down approximate to 0.5-0.8kPa); thus revealing a different perfusion profile to the inverted-U observed in other exercise modes. The afternoon time trial was 3.4s faster (95% confidence interval 0.9-5.8s) and mean power output 3.2% higher (337 vs 347W; P=0.04), in conjunction with similar exercise-induced elevations in MCAv (P=0.60) and reductions in cerebral oxygenation (TOI) (P=0.12). At the muscle, afternoon trials involved similar oxygen extraction (HHb volume and TOI) albeit from a relatively lower total Hb volume (P<0.01). In conclusion, rowing performance was better in the afternoon, but not in conjunction with differences in MCAv or exercise-induced differences in cerebral oxygenation.