Acute cardiac autonomic and haemodynamic responses to leg and arm isometric exercise.

OBJECTIVES: Acute cardiovascular responses following a single session of isometric exercise (IE) have been shown to predict chronic adaptations in blood pressure (BP) regulation. It was hypothesised that exercises which recruit more muscle mass induce greater reductions in BP compared to exercises using smaller muscle mass. To test this hypothesis, the current study aimed to compare the acute haemodynamic and autonomic responses to a single session of isometric wall squat (IWS) and isometric handgrip (IHG) training. METHODS: Twenty-six sedentary participants performed a single IWS and IHG session in a randomised cross-over design, with training composed of 4 × 2-min contractions, with 2-min rest, at 95 HRpeak and 30% MVC respectively. Haemodynamic and cardiac autonomic variables were recorded pre, during, immediately post, and 1-h post-exercise, with the change from baseline for each variable used for comparative analysis. RESULTS: During IWS exercise, there was a significantly greater increase in systolic BP (P < 0.001), diastolic BP (P < 0.001), mean BP (P < 0.001), heart rate (P < 0.001), and cardiac output (P < 0.001), and a contrasting decrease in baroreflex effectiveness index (BEI) and cardiac baroreceptor sensitivity (cBRS). In the 10-min recovery period following IWS exercise, there was a significantly greater reduction in systolic BP (P = 0.005), diastolic BP (P = 0.006), mean BP (P = 0.003), total peripheral resistance (TPR) (P < 0.001), BEI (P = 0.003), and power spectral density (PSD-RRI) (P < 0.001). There were no differences in any variables between conditions 1-h post exercise. CONCLUSIONS: Isometric wall squat exercise involving larger muscle mass is associated with a significantly greater post-exercise hypotensive response during a 10-min recovery window compared to smaller muscle mass IHG exercise. The significantly greater reduction in TPR may be an important mechanism for the differences in BP response.

Continuous Cardiac Autonomic and Hemodynamic Responses to Isometric Exercise.

PURPOSE: Elevated arterial blood pressure (BP) is associated with autonomic dysfunction and impaired hemodynamic control mechanisms. Isometric exercise (IE) training has been demonstrated effective at reducing BP; however, the continuous cardiovascular responses during IE are underinvestigated. We hypothesized that reflex autonomic cardiovascular control is an important mediator in reducing BP. To test our hypothesis, we investigated continuous cardiac autonomic modulation and baroreceptor reflex sensitivity (BRS) in response to IE. METHODS: Twenty-five prehypertensive participants performed a single IE wall squat training session. Total power spectral density (PSD) of HR variability (HRV) and associated low-frequency (LF) and high-frequency (HF) power spectral components were recorded in absolute (ms) and normalized units (nu) before, during, and after an IE session. HR was recorded via electrocardiography and BRS via the sequence method. Continuous BP was recorded via the vascular unloading technique and stroke volume via impedance cardiography. Total peripheral resistance was calculated according to Ohm's law. RESULTS: During IE, there were significant reductions in HRV (P < 0.05) and BRS (P < 0.05) and significant increases in HR (P < 0.001), systolic, diastolic, and mean BP (all P < 0.001). In recovery from IE, HRV (P < 0.001), HFnu (P < 0.001), and BRS (P < 0.001) significantly increased with a significant decrease in LFnu (P < 0.001) and LF:HF ratio (P < 0.001), indicative of predominant parasympathetic over sympathetic activity. This autonomic response was associated with a significant reduction in systolic (23.2 ± 18.1 mm Hg, P < 0.001), diastolic (18.7 ± 16.9 mm Hg, P < 0.001), and mean (15.8 ± 15.5 mm Hg, P < 0.001) BP, below baseline and a significant reduction in total peripheral resistance (P < 0.001). CONCLUSIONS: A single IE session is associated with improved cardiac autonomic modulation and hemodynamic cardiovascular control in prehypertensive males. These acute responses may be mechanistically linked to the chronic reductions in resting BP reported after IE training interventions.