Intoduction: Sufficient blood and oxygen supply to the brain is crucial for optimal performance and exercise tolerance. This study examined the effects of endurance training on oxygen delivery to the right and left prefrontal cortex, hypothesizing that increased aerobic capacity would enhance brain oxygen delivery.

Methods: Sixteen (n=16) male distance runners (age: 34.1±5.1 yrs, body mass: 70.8±4.1 kg) trained five times per week for eight weeks. Training included two high-intensity interval sessions (90-100% VO₂max) and three continuous sessions (70-80% VO₂max). Before and after training VO₂max was assessed on a treadmill and a cycle ergometer. Deoxyhemoglobin (HHb), oxyhemoglobin (O₂Hb), total hemoglobin (tHb), and tissue saturation index (TSI) were recorded using functional multichannel near-infrared spectroscopy to assess local tissue oxygenation in the left and right prefrontal cortex, the vastus lateralis, and the biceps brachialis (inactive muscle) during 10 min of submaximal cycling performed at an intensity 5% below the first ventilatory threshold. Oxygen uptake and hemodynamic data were also collected using respiratory gas exchange and noninvasive photoplethysmography, respectively.

Results: VO₂max increased in both running (from 55.2±1.2 to 58.8±1.8 ml/kg/min, p<0.01) and cycling (from 51.1±2 to 54.3±2.2 ml/kg/min, p<0.01). During the 10-min submaximal exercise, post-training increases were observed in O₂Hb (27.7%), HHb (37.9%) and THb (30.6%) in both the left and right prefrontal cortex (p<0.01). However, TSI decreased in the left (-9.8%, p<0.05) and remained unchanged in the right prefrontal cortex. In the vastus lateralis, O₂Hb (-27.1%), THb (-18.7%) and TSI (-10.4%) decreased (p<0.05), while HHb remained unchanged. Calculated arterio-venous oxygen difference increased (+5.6%, p<0.05) after training. In the inactive biceps brachii muscle, O₂Hb and THb increased (by +59% and +44%, respectively; p<0.05), while HHb and TSI remained unchanged.

Conclusions: Endurance training increases muscle oxygen extraction and reduces blood flow to working muscles, facilitating blood volume redistribution and augmenting oxygen delivery to the brain, during submaximal exercise. The right and left prefrontal cortex appear to adapt differently to endurance training, suggesting distinct functions in regulating aerobic exercise tolerance.

Ethical standards: the study was approved by the University’s Ethical Committee for human experimentation and conformed to the Declaration of Helsinki.