Non-invasive assessment of ribcage inspiratory muscle fatigue during two endurance tests in healthy subjects


Introduction: Fatigue is defined as a loss in the capacity for developing force and/or velocity of a muscle which is reversible by rest. The aim was to evaluate non-invasively the fatigue and recovery of the inspiratory ribcage muscles during two endurance tests in healthy subjects. Methods: 22 subjects were evaluated before, during and after performing a respiratory endurance test with normocapnic hyperpnea (NH) and inspiratory pressure threshold load (IPTL). Simultaneous measurements of muscle activity (electromyography), tissue oxygenation (NIRS), pressure (nasal inspiratory pressure), and volume (optoelectronic plethysmography) were performed. Results: There was a decrease in the maximum relaxation rate (MRR) and increase in the time constant ($τ$) after the IPTL test (p <0.05) and a decrease in the peak pressure generated in SNIP after both protocols (p <0.05). Additionally, there was a decrease in shortening velocity and mechanical power only after the IPTL test (p <0.05). The inspiratory ribcage muscles showed a linear drop in the median frequency in the IPTL test and an exponential drop in the NH test, which was not signi?cant for the development of fatigue and there was a linear increase in the NIRS variables in both protocols. Conclusion: It was concluded that the inspiratory ribcage muscles undergo changes after performing an endurance test with NH and IPTL. Additionally, the development of fatigue in these muscles and their consequent changes are more evident in the protocol with IPTL.

Clinical respiratory physiology, exercise and functional imaging