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<br />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 barorefex 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 signifcantly greater post-exercise hypotensive response during a 10-min recovery window compared to smaller muscle mass IHG exercise. The signifcantly greater reduction in TPR may be an important mechanism for the diferences in BP response.