Comparison Of Oxygenation In The Frontal Cortex Between Low- And High-intensity Cycling Exercise: A NIRS Study

Cerebral blood flow (CBF) and oxygen metabolism change during continuous exercise depending on exercise intensity in accordance with the magnitude of exertion. Perception of effort and will to perform exercise are closely related with function of the prefrontal cortex (PFC) and the underlying physiological mechanisms remain to be elucidated. To estimate changes in cerebral metabolic rate for oxygen (CMRO2) and CBF in the PFC during exercise, near-infrared time resolved spectroscopy (TRS) has advantages since absolute changes in cerebral blood volume (CBV) and cerebral hemoglobin oxygen saturation (ScO2) can be detected. PURPOSE: To identify if exercise induced changes of CMRO2 and CBV in the PFC may differ between low- and high-intensity exercise, and to clarify if the association between cerebral perfusion and oxygen metabolism may be affected. METHODS: Twelve recreationally active men (age, 24 ± 6 years) performed 15-min of low-intensity constant-load cycling exercise (ExL; 33 ± 6% VO2max), while ten men of identical characteristics (age, 21 ± 1 years) performed the similar bout of high-intensity (ExH; 64 ± 8% VO2max). Respiratory and cardiovascular parameters and the rate of perceived exertion (RPE) were measured. Cerebral oxygenation in both sides of PFC was measured during ExL and ExH by TRS indicating ScO2 and total hemoglobin concentration ([HbT]), an index of CBV. Changes from the baseline in CBV (rCBV), CMRO2 (rCMRO2) and oxygen extraction fraction (rOEF) were estimated, assuming a constant power law relationship between CBF and CBV. Comparisons for variables were made using two-way ANOVA with repeated measures. RESULTS: RPE differed between ExL and ExH, 8.8 ± 1.1 and 13.1 ± 1.6 a.u. in Borg scale. Compared with ExL, rCBV after ExH increased significantly (p < 0.0026) in the left PFC by 13%, as rCMRO2 induced by exercise did not different between ExL and ExH for both sides of PFC. (p = 0.49 and 0.84, in the right and left). rOEF correlated with rCMRO2 greater in ExL (R2 = 0.81) compared with ExH (R2 = 0.44). CONCLUSIONS: Dynamic exercise induces dissociated relationships in cerebral perfusion and oxygen metabolism in a manner that CMRO2 would be preserved by OEF depending on exercise intensity. Our results imply that changes in this relationship may reflect the function of the PFC associated with perception of effort.