Male versus Female Forebrain Associations with Cardiodynamic Response during Isometric Exercise

Abstract

The present study examined the cortical network associated with cardiac adjustments during the first 30 sec of isometric handgrip exercise and how this network is affected by sex differences. Healthy men (n=10) and women (n=10) completed four trials of 5% and 35% maximal voluntary contraction (MVC) handgrip exercise in two separate sessions. Heart rate (HR) and cortical activities were measured during the functional magnetic resonance imaging (fMRI) session while arterial blood pressure (MAP), HR and muscle sympathetic nerve activity (MSNA) were recorded during a separate session. Both male and female showed significant increase in HR and MAP during the 35% relative to 5% MVC trials (p<0.001) with a handgrip x sex interaction observed in HR (p<0.03). There was no MSNA response to either exercise level. Relative to the 5% MVC trials, stronger activities at the motor cortex and the cerebellum and stronger deactivation at the medial frontal gyrus and the left inferior parietal gyrus were observed during the 35% MVC trails. The left anterior insula was deactivated in female but not in male during the 35% MVC trials. These findings revealed that a complex cortical network is associated with rapid cardiovascular response to exercise in both men and women. The small variations in cortical activity between men and women may contribute to the sex-specific heart rate responses at the onset of isometric exercise. Supported by Heart and Stroke Foundation of Ontario, and Canadian Space Agency.