High intensity, low volume inspiratory muscle strength training (IMST) has favorable effects on casual systolic blood pressure and systemic vascular resistance. However, the acute effects of IMST on heart rate (HR), blood pressure (BP) and sympathetic regulation of vascular resistance and the trajectory of post exercise recovery are not known. We recruited fourteen young adults (7 women/7 men, age: 22±2 years) to perform a single bout of high intensity IMST (inspiratory resistance set at 75% of maximal inspiratory pressure) importantly, female and male subjects were matched in regard to the target inspiratory pressure and target inspiratory muscle work per breath. We recorded HR, beat-to-beat changes in BP and postganglionic, muscle sympathetic nerve activities (MSNA) continuously throughout Baseline, a single bout of IMST (comprising five sets of 6 inspiratory efforts) and in Recovery. We show that one bout of IMST does not effect a change in BP however, it effects a significant increase in HR (68.4 ±11.7 BPM vs. 85.4 ±13.6 BPM; p<0.001) and a significant decline in MSNA (6.8 ±1.1 bursts/15s bin; p<0.001 vs. 3.6 ±0.6 bursts/15s bin) relative to Baseline. Remarkably, among men MSNA rebounded to Baseline levels within the first minute of Recovery however in women, MSNA suppression persisted for 5 minutes. We show that in healthy young adults, high intensity, low volume respiratory training results in the acute suppression of MSNA. Importantly, MSNA suppression is of greater magnitude and longer duration in women than in men.

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Previous studies indicate inspiratory muscle strength training (IMST) may attenuate blood pressure (BP) and heart rate (HR) responsiveness to sustained respiratory muscle work. However, these previous studies used a less vigorous IMST intervention and did not have subjects gauge perception of respiratory effort. Our objective in this study was to evaluate the effects of 6 weeks high intensity (75% maximum inspiratory pressure), low volume (5 sets of 6 breaths/day) IMST on BP and HR responses to a resistive breathing trial (RBT) to exhaustion (target pressure = 65% of maximal inspiratory pressure or PImax; duty cycle = 0.7; breathing frequency matched to eupnea). We recruited 10 (7M; 3F) healthy young adults to complete two RBT, pre‐ and then again post‐, 6 weeks IMST. Throughout the RBT we assessed beat‐to‐beat changes in BP and HR, inspiratory pressure, respiratory muscle work (mmHg.s) and recorded participant ratings of perceived exertion (RPE) via the Borg scale. We report significant IMST‐related improvements in endurance time (PRE: 362.0 ±46.6s vs. POST: 663.8 ±110.3s, p=0.003) and respiratory muscle work (PRE: ‐9445 ±1562mmHg.s vs. POST: ‐16648 ±3761mmHg.s, p=0.069). Remarkably, despite significant gains in work and endurance, the latter stages of the post RBT were characterized by a reduced cardiovascular responsiveness (i.e., SBP, DBP and HR) and lower RPE, consistent with a blunting of the metaboreflex.

Background Our laboratory has shown that an abbreviated form of inspiratory muscle strength training (IMST) performed 5 minutes/day, 5 days/week for 6 weeks lowers casual systolic blood pressure and systemic vascular resistance in healthy young adults. While the effects of IMST have been characterized in the short term, the acute effects of the training protocol on cardiovascular function have not been documented. Purpose To characterize the acute cardiovascular response to a bout of IMST (comprising 5 sets of 6 breaths) in healthy young adults. Methods Fourteen healthy women and men (n=14, 7F/7M, age: 22±2 years) performed five sets of six inspiratory efforts against a target resistance set at 75% of maximum inspiratory pressure (PImax). We recorded inspiratory pressure, postganglionic, multiunit muscle sympathetic nerve activity (MSNA), beat‐to‐beat changes in blood pressure (SBP and DBP), and heart rate (HR) at baseline, during IMST and in recovery. Results There were no differences between women and men in regard to PImax (F: −79.9±17.7 and M: −78.3±21.7 mmHg, p=0.8794), or baseline measures of MSNA (F: 7.3±1.8 bursts/15s bin and M:6.2±1.4 bursts/15s bin, p=0.6377), SBP (F:114.0±9.1 and M:114.0±4.7 mmHg, p=0.9855), and HR (F: 75±8 bpm and M:74±15 bpm, p=0.6994). During IMST, women and men attained the same target pressure (75% PImax) (F: −58.6±13.0 mmHg and M: −58.7 ±16.3 mmHg, p=0.8794) and performed the same amount of inspiratory work per breath (F: 84.1±22.2 and M: 85.0±25.9 mmHg.s, p=9176). Relative to baseline, HR increased 25±10%, (p<0.0001) and MSNA decreased 43±20% (p<0.0001) in all subjects. In recovery, MSNA suppression persisted in women but not in men (p=0.015). There were no acute effects of IMST on systolic (p=0.895) or diastolic (p=0.761) blood pressures. Conclusion IMST exerts an acute inhibitory effect on MSNA in young men and women. Our data highlight a disparity in the time course of the recovery of MSNA post IMST for women vs. men. Support or Funding Information National Institutes of Health Interdisciplinary Training Grant in Cardiovascular Sciences T32 HL007249