High‐intensity, low‐volume inspiratory muscle strength training blunts the cardiovascular response to constant load respiratory testing

Abstract

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.