Handgrip exercise does not alter CO2 -mediated cerebrovascular flow-mediated dilation.

Abstract

Handgrip exercise (HG), a small muscle exercise, improves cognitive function and is expected to provide a useful exercise mode to maintain cerebral health. However, the effect of HG on cerebral blood flow regulation is not fully understood. The present study aimed to examine the effect of acute HG on cerebral endothelial function as one of the essential cerebral blood flow regulatory functions. Thirteen healthy young participants performed interval HG, consisting of 4 sets of 2min HG at 25% of maximum voluntary contraction with 3min recovery between each set. Cognitive performance was evaluated before and at 5 and 60min after interval HG using the Go/No-Go task (reaction time and accuracy). The diameter and blood velocity of the internal carotid artery (ICA) were measured using a duplex Doppler ultrasound system. To assess cerebral endothelial function, hypercapnia (30s of hypercapnia stimulation, end-tidal partial pressure of CO2 : +9mmHg)-induced cerebrovascular flow-mediated dilatation (cFMD) was induced, calculated as relative peak dilatation from baseline diameter. The shear rate (SR) was calculated using the diameter and blood velocity of the ICA. As a result, cognitive performance improved only at 5min after interval HG (reaction time, P=0.008; accuracy, P=0.186), whereas ICA SR during interval HG and cFMD after interval HG were unchanged (P=0.313 and P=0.440, respectively). These results suggest that enhancement in cerebral endothelial function is not an essential mechanism responsible for acute HG-induced cognitive improvement. NEW FINDINGS: What is the central question of this study? Does handgrip exercise, a small muscle exercise, improve cerebral endothelial function? What is the main finding and its importance? Acute interval isometric handgrip exercise (2min of exercise at 25% maximum voluntary contraction, followed by 3min of recovery, repeated for a total of 4 sets) did not improve cerebral endothelial function. Since the cerebrovascular shear rate did not change during exercise, it is possible that acute handgrip exercise is not sufficient stimulation to improve cerebral endothelial function.