Competing Demands: Acute Effects of Inspiratory Load on Hemodynamics and Vastus Lateralis Deoxygenation During Cycling

Recently, the combination of inspiratory muscle resistance (IMR) training with aerobic exercise has become a common practice, driven by the expectation of optimizing training outcomes. However, performance during aerobic exercise may be limited by increased respiratory effort and activation of the inspiratory muscle metaboreflex. Despite this, the acute effects of this combined approach are not yet fully understood. Therefore, this study aimed to investigate how inspiratory muscle resistance (IMR) influences performance, cardiovascular responses, and muscle oxygenation in healthy young men. Ten participants completed four visits: (I) cardiopulmonary exercise testing to determine ventilatory anaerobic threshold (VAT), (II) inspiratory muscle strength assessment, and (III-IV) two constant-load cycling sessions, preceded by either IMR at 30% of S-Index or a sham condition at 10%. Exercise tolerance (time to exhaustion, Tlim), heart rate variability (HRV), blood pressure, respiratory rate, and vastus lateralis muscle oxygenation were evaluated. Tlim was significantly reduced in the IMR condition compared to sham (<i>p</i> = .03), indicating decreased exercise tolerance. HRV showed expected autonomic responses during exercise, with no significant differences between conditions. Blood pressure and respiratory rate increased similarly during both sessions. Muscle deoxygenation profiles were generally comparable; however, Near-Infrared Spectroscopy (NIRS) revealed significantly greater deoxyhemoglobin concentration at peak exercise during IMR (<i>p</i> < .05), suggesting enhanced muscle oxygen extraction. In conclusion, IMR combined with aerobic exercise acutely reduces exercise tolerance but does not exacerbate cardiovascular stress, supporting its safety in healthy individuals. Nevertheless, increased metabolic demand may explain the reduced endurance observed.