Agreement between left and right middle cerebral artery blood velocity responses to incremental and constant work-rate exercise in healthy males and females.

To quantify the agreement between left and right middle cerebral artery blood velocity (MCAv) responses to incremental and constant work-rate exercise in adults.Seventeen healthy adults (23.8 ± 2.4 years, 9 females) completed a ramp incremental test to exhaustion on a cycle ergometer, three 6-minute transitions at a moderate-intensity, and three at a heavy-intensity, all on separate days. Bilateral MCAv was measured throughout using transcranial Doppler ultrasonography, with left and right MCAv data analysed separately. Data were analysed at baseline, gas exchange threshold, respiratory compensation point and exhaustion during ramp incremental exercise. MCAv responses to constant work-rate exercise were analysed using a mono-exponential model, to determine time- and amplitude-based kinetic response parameters.Left and right MCAv responses to incremental and constant work-rate exercise were significantly, strongly and positively correlated (≥ 0.61,< 0.01). Coefficient of variation (left versus right) ranged from 7.3%-20.7%, 6.4%-26.2% and 5.9%-22.5% for ramp, moderate and heavy-intensity exercise, respectively. The relative change in MCAv from baseline was higher in the right compared to left MCAv during ramp, moderate and heavy-intensity exercise (all< 0.05), but the effect sizes were small (≤ 0.4). Small mean left-right differences were present during ramp incremental exercise at all time-points (<6 cm s; <4%), and for all kinetic parameters during moderate and heavy-intensity exercise (<3 cm s, <3%, <4 s).These findings demonstrate similarities between left and right MCAv responses to incremental and constant-work rate exercise in adults on a group-level, but also highlight individual variation in the agreement between left and right MCAv exercise responses.