Acute Cardiorespiratory Responses to Inspiratory Pressure Threshold Loading

Purpose: We tested the acute responses to differing pressure threshold inspiratory loading intensities in well-trained rowers. The purpose of this study was to evaluate 1) how the magnitude of inspiratory pressure threshold loading influences repetition maximum (RM), tidal volume (VT), and external work undertaken by the inspiratory muscle; and 2) whether the inspiratory muscle metaboreflex is activated during acute inspiratory pressure threshold loading. Methods: Eight males participated in seven trials. Baseline measurements of maximal inspiratory pressure(PImax), resting tidal volume (VT), and forced vital capacity (FVC) were made. During the remaining sessions, participants undertook a series of resistive inspiratory breathing tasks at loads corresponding to 50%, 60%, 70%, 80%, and 90% of PImax using a pressure threshold inspiratory muscle trainer. The number of repetitions completed at each load, VT, heart rate (fc), and measures of arterial blood pressure was assessed continuously during
each trial. Results: A standardized cutoff of 10% FVC was used to define the RM, which decreased as loading intensity increased (P < 0.05). This response was nonlinear, with an abrupt decrease in RM occurring at loads >70% of PImax. The most commonly used inspiratory muscle training regimen of 30RM corresponded to 62.5% +/- 4.6% of PImax and also resulted in the highest external work output. Tidal volume (VT) decreased significantly over time at 60%, 70%, and 80% of PImax (P < 0.05), as did the amount of external work completed (P < 0.05). Conclusions: Although all loads elicited a sustained increase in fc, only the 60% load elicited a sustained rise in mean arterial blood pressure (P = 0.016), diastolic blood pressure (P = 0.015), and systolic blood pressure (P = 0.002), providing evidence for a metaboreflex response at this load.