Acute Effects of Different Inspiratory Muscle Training Intensities on Intercostal Muscle Oxygenation in Healthy Adults: A Randomized Crossover Study.
Abstract
Background
Increased inspiratory loading increases oxygen consumption and metabolic demand in the respiratory muscles, affecting muscle oxygenation. However, evidence regarding different inspiratory muscle training (IMT) intensities on intercostal muscle oxygenation remains limited. This study compared acute effects of different IMT intensities on intercostal muscle oxygenation and cardiorespiratory responses.
Methods
This randomized, single-blind, crossover study included 30 healthy individuals. Participants performed IMT at 0% (sham), 30% maximal inspiratory pressure (endurance-based) (MIP), and 70% MIP (strength-based) in randomized order. Intercostal muscle oxygen saturation (SmO₂) and total hemoglobin (THb) were assessed near-infrared spectroscopy. Respiratory muscle strength (mouth pressure device) endurance (incremental threshold loading test), heart rate, peripheral oxygen saturation [pulse oximeter (SpO₂)] and dyspnea and fatigue (Modified Borg Scale) were evaluated.
Results
No significant difference was observed in resting SmO₂ among the training intensities (p=0.337). Minimum SmO₂, maximum SmO₂, and ΔSmO₂ differed significantly according to training intensity (p<0.001). The 70% MIP protocol resulted in lower minimum and maximum SmO₂ values and a greater ΔSmO₂ than the sham and 30% MIP protocols. Maximum THb and ΔTHb were also significantly higher during the 70% MIP protocol. ΔHR, perceived dyspnea, and fatigue were significantly greater 70% MIP protocol than the sham and 30% MIP protocols (p<0.05).
Conclusions
High intensity IMT (70% MIP) induced greater intercostal muscle deoxygenation and increase in total hemoglobin than sham and endurance IMT. High-intensity loading also induced greater increases in heart rate, perceived dyspnea, and fatigue. These findings suggest that physiological responses different IMT intensities should be considered when designing IMT programs.