Respiratory muscle oxygenation kinetics: Relationships with breathing pattern during exercise

This work aimed to investigate accessory respiratory muscle oxygenation (RMO2) during exercise, using near-infrared spectroscopy, and to study relationships between RMO2 kinetics and breathing parameters. Nineteen young males (19.3 +/- 1.5 years) performed a maximal incremental test on a cycle ergometer. Changes in breathing pattern were characterized by accelerated rise in the breathing frequency (f(Racc)), plateau of tidal volume (V-Tplateau) and inflection point in the VENT relationship (V-E/V-Tinflection). First and second ventilatory thresholds (VT1 and VT2) were also determined. RMO2 kinetics were monitored by NIRS on the serratus anterior. During exercise, all subjects showed reduced RMO2 (deoxygenation) with a breakdown (B-RMO2) at submaximal workload (86% VO(2)max). VO2 corresponding to B-RMO2 and to f(Racc), V-Tplateau, V-E/V-Tinflection, or VT2 were not different. Relationships were found between the VO2 at B-RMO2 and the VO2 at f(Racc) (r=0.88, P < 0-001), V-Tplateau (r=0.84, p < 0.001), V-E/V-Tinflection (r=0.58, p < 0.05) or VT2 (r = 0.79, p < 0.001). The amplitude of RMC, at maximal workload was weakly related to VO2max (r = 0.58, p < 0.05). B-RMO2 seems to be due to the change in breathing pattern and especially to the important rise in breathing frequency at the VT2 exercise level. Moreover, subjects who exhibit higher VO2max also exhibit a higher decrease in respiratory muscle oxygenation during exercise.