Physical Activity and Fitness Levels on Cerebral Hemodynamics: A Systematic Review

Background Physical activity (PA) and fitness have been linked to improved cerebrovascular function, yet no comprehensive synthesis has integrated evidence across measurement techniques. This review examines the sustained effects of PA and fitness on cerebral hemodynamics using functional near‐infrared spectroscopy (fNIRS), transcranial Doppler (TCD), and magnetic resonance imaging (MRI), focusing on observational designs to capture long‐term adaptations rather than acute exercise responses. Methodology A systematic search was conducted in Web of Science and MEDLINE until September 14, 2024. Studies measuring cerebral hemodynamics in individuals with varying PA and fitness levels were included, whereas those with pathological conditions were excluded. Results Eighteen studies were included. fNIRS studies showed that higher fitness was associated with greater oxyhemoglobin (HbO2) response during cognitive tasks, although effects varied by age and sex. TCD studies indicated elevated middle cerebral artery velocity (MCAv) and cerebrovascular reactivity (CVR) in trained individuals, particularly under hypercapnic conditions, but with mixed findings in older and less active populations. MRI studies revealed that higher aerobic fitness was associated with lower resting cerebral blood flow (CBF), suggesting improved neurovascular efficiency. Across modalities, a convergent pattern emerged linking PA and fitness to favorable cerebral hemodynamic adaptations, modulated by age, sex, exercise type, and measurement techniques. Conclusion This review shows that PA and fitness are associated with more favorable cerebral hemodynamics, including oxygenation, blood flow, and vascular reactivity, with convergent evidence across fNIRS, TCD, and MRI. However, these effects are modulated by age and sex, and evidence remains concentrated in young and older adults and on aerobic exercise, warranting further research across populations and exercise modalities.