Coupling between global brain blood oxygen level‐dependent activity and cerebrospinal fluid dynamics in young endurance athletes

Cerebrospinal fluid (CSF) contributes to brain waste clearance through its coupling with cerebral haemodynamics. Aerobic exercise promotes brain health, but its influence on brain waste clearance remains unclear. This study examined the coupling between CSF and cerebral haemodynamics in endurance athletes. Fifteen young male endurance athletes were compared with 16 age-matched sedentary male controls. Resting-state functional magnetic resonance imaging was used to obtain brain global blood oxygen level-dependent (gBOLD) and CSF inflow signals. The gBOLD-CSF coupling was estimated using cross-correlation function and transfer function analyses in time and frequency domains, respectively. The magnitude of gBOLD and CSF oscillations was also quantified by power spectral density. The cross-correlation-derived gBOLD-CSF coupling was similar between athletes and sedentary controls (-0.30 ± 0.26 vs. -0.33 ± 0.22, P = 0.753). Power spectral density of the CSF inflow signal was significantly greater in athletes (2.83 [2.19, 3.47] z²/Hz) than sedentary individuals (1.84 [1.22, 2.46] z²/Hz, P = 0.030), whereas that of the gBOLD signal did not differ between groups. Although transfer function gain did not show a statistically significant group difference, a moderate effect size was observed (1.50 [-0.36, 3.36] vs. 1.24 [-0.06, 2.55], P = 0.051, effect size: 0.523). Transfer function phase and coherence were comparable between groups. Significant frequency dependence was observed for gBOLD power spectral density as well as transfer function gain, phase and coherence across groups. Endurance athletes demonstrated greater CSF fluctuation compared with sedentary individuals. Our findings suggest that endurance training may be linked to changes in CSF dynamics.