Cerebral blood flow responses to aquatic treadmill exercise

Introduction. Aquatic treadmills are used as a rehabilitation method for conditions such as spinal cord injury, osteoarthritis and stroke, and can facilitate an earlier return to exercise training for athletes. However, their effect on cerebral blood flow (CBF) responses has not been examined. We tested the hypothesis that aquatic treadmill exercise would augment CBF and lower heart rate compared to land-based treadmill exercise. Methods: Eleven participants completed incremental exercise (crossover design) starting from walking pace [4 km/h, immersed to iliac crest (aquatic), 6 km/h (land)] and increasing 1 km/h every 2 min up to 10 km/h for aquatic (maximum belt speed) or 12 km/h for land. Following this, participants completed two 2-min bouts of exercise immersed to mid-thigh and mid-chest at constant submaximal speed (aquatic), or were ramped to exhaustion (land; increased gradient 2° every min). Middle cerebral flow velocity (MCAv) and heart rate (HR) were measured throughout, and the initial 10 min of each protocol and responses at each immersion level were compared. Results. Compared to land-based treadmill, MCAvmean increased more from baseline for aquatic exercise (21 vs. 12%; p<0.001), while being associated with lower overall HR (pooled difference: 11 b/min; p<0.001). MCAvmean increased similarly during aquatic walking compared to land-based moderate intensity running (~10 cm/s; p=0.56). Greater water immersion lowered HR (139 vs. 178 b/min for mid-chest vs. mid-thigh), while MCAvmean remained constant (P=0.37). Conclusion. Findings illustrate the potential for aquatic treadmill exercise to enhance exercise-induced elevations in CBF, and thus optimise shear-stress mediated adaptation of the cerebrovasculature.