Continuous cardiac autonomic and haemodynamic responses to isometric exercise in females

Purpose: Hypertension is associated with impaired haemodynamic control mechanisms and autonomic dysfunction. Isometric exercise (IE) interventions have been shown to improve autonomic modulation and reduce blood pressure (BP) in predominantly male participants. The physiological responses to IE are under explored in female populations; therefore, this study investigated the continuous cardiac autonomic and haemodynamic response to a single bout of IE in a large female population.

Methods: Forty physically inactive females performed a single, individually prescribed isometric wall squat training session. Total power spectral density of heart rate variability (HRV) and associated low frequency (LF) and high-frequency (HF) power spectral components, were recorded in absolute (ms2) and normalised units (nu) pre, during and post an IE session. Heart rate (HR) was recorded via electrocardiography and baroreceptor reflex sensitivity (BRS) via the sequence method. Continuous blood pressure was recorded via the vascular unloading technique and stroke volume via impedance cardiography. Total peripheral resistance (TPR) was calculated according to Ohm’s Law.

Results: During IE, there were significant reductions in HRV (p<0.001) and BRS (p<0.001), and significant increases in heart rate (p<0.001), systolic, mean and diastolic BP (p<0.001 for all). In recovery following the IE session, cardiac autonomic parameters returned to baseline (p=0.974); however, total peripheral vascular resistance significantly reduced below baseline (p<0.001). This peripheral vascular response was associated with significant reductions in systolic (-17.3±16.5 mmHg, p<0.001), mean (-18.8±17.4 mmHg, p<0.001) and diastolic BP (-17.3±16.2 mmHg, p<0.001), below baseline.

Conclusion: A single IE session is associated with improved haemodynamic cardiovascular responses in females. Cardiac autonomic responses return to baseline values, which suggests alternative mechanisms are responsible for the post exercise haemodynamic improvements in females. Future mechanistic research is required to investigate the acute and chronic effects of IE in female populations with different resting BP profiles.