Baroreflex and autonomic responses to two equated isometric resistance exercise protocols in females

Different resistance exercise set configurations seem to lead to distinct hemodynamic, baroreflex and autonomic responses. Nevertheless, both the baroreflex and the autonomic reactivity to an equated work-to-rest ratio (W:R-equated) isometric exercise (IE) session in females still must be clarified. Thus, the present work investigated the autonomic and baroreflex responses of two W:R-equated isometric exercise sessions in female participants. Nine healthy females (25 ± 3 years) performed two isometric protocols equated by W:R with 30% 1-RM - a long set configuration (LSC): 4 sets x 2 min isometric x 2 min rest; and a short set configuration (SSC): 16 sets x 30 s isometric x 24s rest. Blood pressure (BP) and cardiac intervals were monitored by photoplesthysmography and electrocardiogram before, during and after (immediately, 30 and 60 min) exercise. The time domain parameters and frequency domain measures of the heart rate variability were calculated along with the baroreflex gain and effectiveness. A two-way repeated measures ANOVA was applied. Both protocols evoked a reduction in the baroreflex gain, whereas the LSC gain reduction lasted longer (30 and 60 minutes). Only the SSC was able to lower the root mean square of successive differences between normal heart beats (RMSSD) during exercise, when compared to pre-session values (p < 0.05). The standard deviation of the normal-to-normal interval (SDNN) increased during exercise with the LSC protocol (p<0.05). The high-frequency (HF) band only decreased during exercise using the SSC protocol (p < 0.05), while the LF/HF ratio was also only elevated in the SSC during exercise (p<0.05). The LSC evoked more prolonged reductions in the baroreflex gain, while the SSC protocol caused a greater disturbance in cardiac autonomic modulation.