Does treadmill walking affect neurovascular coupling during cognitive activation in healthy individuals?

Treadmill desks have become increasingly popular in the workplace to improve physical health. However, it is unknown whether treadmill walking affects neurovascular coupling, which is the increase in cerebral blood flow during cognitive tasks. Additionally, it is unknown whether the speed of treadmill walking affects neurovascular coupling or if there is a sex difference in the response. A total of 49 subjects (22 male, 27 female) walked on a treadmill at four different walking speeds (0.5 mph, 1.5 mph, 2.5 mph and 3.5 mph) in addition to a standing condition (0 mph). While standing or walking at each speed, participants also performed the Stroop color-word test. Continuous cerebral flow velocity in the right middle cerebral artery (MCAv), blood pressure, heart rate, and end-tidal CO2 were measured throughout testing. The percent increase in MCAv from the no tasking condition (standing or walking at each speed) to the Stroop tasking condition (Stroop + standing or walking at each speed) was analyzed to measure neurovascular coupling. Results showed a significant effect of walking speed (p=0.003) as well as a significant interaction between walking speed and sex (p=0.012) on the percent increase in MCAv during the Stroop tasking condition (0 mph: Men = 2.6 ± 5.8%, Women = 1.8 ± 3.7%; 0.5 mph: Men = 2.3 ± 4.2%, Women = 3.6 ± 5.2%; 1.5 mph: Men = 4.1 ± 6.2%, Women = 4.2 ± 4.9%; 2.5 mph: Men = 3.4 ± 7.4%, Women = 4.0 ± 4.3%; 3.5 mph: Men = −1.7 ± 7.8%, Women = 3.4 ± 7.0%). There was also a small, but significant effect of walking speed on the difference in end-tidal CO2 between the Stroop tasking condition and the no tasking condition within each speed (p=0.005; 0 mph: Men = 0.0 ± 1.1 mmHg, Women = −0.1 ± 1.4 mmHg; 0.5 mph: Men = −0.1 ± 0.8 mmHg, Women = 0.0 ± 0.7 mmHg; 1.5 mph: Men = 0.0 ± 1.3 mmHg, Women = 0.2 ± 0.9 mmHg; 2.5 mph: Men = 0.4 ± 1.7 mmHg, Women = 0.1 ± 0.9 mmHg; 3.5 mph: Men = −1.0 ± 2.0 mmHg, Women = −0.2 ± 1.1 mmHg). There was no interaction between speed and sex in end-tidal CO2. This data suggests that there is a small, but significant reduction in neurovascular coupling in men during the Stroop test at 3.5 mph, but this reduction may be partially explained by the reduction in end-tidal CO2. This study highlights that neurovascular coupling is preserved during treadmill walking across the slower walking speeds. However, neurovascular coupling at 3.5 mph needs to be further examined with controlled levels of end-tidal CO2 to support whether neurovascular coupling is reduced at this faster walking speed in men.