Estimation of Cerebral Hemodynamics and Oxygenation During Various Intensities of Rowing Exercise: An NIRS Study

This study aimed to investigate changes in cerebral hemodynamics and oxygenation at moderate, heavy, maximal and supramaximal intensities of rowing exercise. It also examined whether these changes reflect alterations in sensation of effort and mood. We also aimed to examine the effects of peak pulmonary oxygen consumption ( $$ O_2p ) on cerebral oxygenation.

Eleven rowers, consisting out of six athletes and five recreational rowers [two female; age, 27 ± 9 years; height, 171 ± 7 cm, body mass, 67 ± 9 kg; $$ O_2p , 53.5 ± 6.5 mL min^-1 kg^-1] rowed a 13-min session separated by 10 and 3 min, at 70 (Ex_70%) and 80% of $$ O_2p (Ex_80%), respectively, on a rowing ergometer, followed by three sessions of 1-min supramaximal exercise (ExSp). After a warm-up at 60% of $$ O_2p (ExM), seven male rowers performed a 2,000 m all-out test (Ex₂₀₀₀). Cardiovascular and respiratory variables were measured. Cerebral oxygenation was investigated by near-infrared time-resolved spectroscopy (TRS) to measure cerebral hemoglobin oxygen saturation (ScO₂) and total hemoglobin concentration ([HbT]) in the prefrontal cortex (PFC) quantitatively. We estimated the relative changes from rest in cerebral metabolic rate for oxygen (rCMRO₂) using TRS at all intensities. During Ex_70% and Ex_80%, ratings of perceived exertion (RPE) were monitored, and alteration of the subject's mood was evaluated using a questionnaire of Positive-and-Negative-Affect-Schedule after Ex_70% and Ex_80%.

When exercise intensity changed from Ex_70% to Ex_80%, the sense of effort increased while ScO₂ decreased. [HbT] remained unchanged. After Ex_70% and Ex_80%, a negative mood state was less prominent compared to rest and was accompanied by increases in both ScO₂ and [HbT]. At termination of Ex₂₀₀₀, ScO₂ decreased by 23% compared to rest. Changes in ScO₂ correlated with $$ O_2p only during Ex₂₀₀₀ (r = -0.86; p = 0.01). rCMRO₂ did not decrease at any intensities.

Our results suggest that alterations in the sense of effort are associated with oxygenation in the PFC, while positive changes in mood status are associated with cerebral perfusion and oxygen metabolism estimated by TRS. At exhaustion, the cerebral metabolic rate for oxygen is maintained despite a decrease in ScO₂.