Respiratory Muscle Oxygenation Kinetics: Relationships with Breathing Pattern during Exercise

This work aimed to investigate accessory respiratory muscle oxygenation (RMO 2 ) during exercise, using near-infrared spectroscopy, and to study relationships between RMO 2 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 TPateau ) and inflection point in the V E /V T relationship (V E /V Tinflection ). First and second ventilatory thresholds (VT1 and VT2) were also determined. RMO 2 kinetics were monitored by NIRS on the serratus anterior. During exercise, all subjects showed reduced RMO 2 (deoxygenation) with a breakdown (B-RMO 2 ) at submaximal workload (86% VO 2max ). VO 2 corresponding to B-RMO 2 and to fracc, V Tplateau, V E /V Tinflection, or VT2 were not different. Relationships were found between the VO 2 at B-RMO 2 and the VO 2 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 RMO 2 at maximal workload was weakly related to VO 2max (r=0.58, p<0.05). B-RMO 2 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 VO 2max also exhibit a higher decrease in respiratory muscle oxygenation during exercise.