Assessment of work load intensity in respiratory muscle training

Purpose: The respiratory muscles can be trained like the other skeletal muscles. However, due to the complexity of the thoracopulmonary system, the assessment of work load intensity during training still remains a complicated matter. Therefore, the aim of this study was to evaluate the feasibility of work load intensity quantification during a period of respiratory muscle training. Methods: Seven healthy participants performed a four-week respiratory muscle training under normocapnic hyperpnoea using a device that allows a constant isocapnic end-tidal CO2 fraction via a two-way piston valve connected to a rebreathing bag. The size of the bag was adjusted to 50–60% of the subject’s vital capacity, with a breathing frequency such that requested ventilation corresponded to 50–60% of maximal voluntary ventilation. Participants trained about 24 min per session (5 min of exercise/1 min of rest, 4 times), 3 days a week, for 4 weeks. The isocapnic device estimated the entire breath-volume during training. At the end of each training session, we asked to provide a rating of the perceived exertion (sRPE, a.u.; CR-10 scale). Results: A moderate correlation between the entire breath-volume during training and the sRPE was found in all training sessions (r = 0.54; p\ 0.01), while moderate to very strong correlations were found for each participant (r = 0.58; p\ 0.05–r = 0.96; p \0.01). Conclusions: The findings of this study suggest that the sRPE, a cost-effective monitoring tool, could be a valid approach to assess training work load during respiratory muscle training.