Respiratory muscle endurance, oxygen saturation index in vastus lateralis and performance during heavy exercise

• The objectives were to investigate the relationship between respiratory muscle endurance, oxygen tissue saturation index dynamics and the time to exhaustion during a constant-load exercise at 90% of VO2max.
• The respiratory muscle endurance was tested with an incremental respiratory exercise by SpiroTiger® which enabled partial rebreathing and voluntary normocapnic hyperpnea.
• O2 tissue saturation index (TSI) kinetics was recorded by a near-infrared spectroscopy device (NIRS) in vastus lateralis.
• The TSI remained steady between 20 and 80% of TTE. Between 80 and 100% of TTE (7.5 ± 6.1%, p < 0.05) a significant drop in TSI concomitant with a minute ventilation increase (16 ± 10 l min−1) was observed.
• Significant correlations between respiratory muscle endurance, the TSI time plateau (between 20 and 80% TL90) and time to exhaustion were observed.

The purpose of this study was to investigate the relationships between respiratory muscle endurance, tissue oxygen saturation index dynamics of leg muscle (TSI) and the time to exhaustion (TTE) during high intensity exercise. Eleven males performed a respiratory muscle endurance test, a maximal incremental running field test (8 km h−1 + 0.5 km h−1 each 60 s) and a high-intensity constant speed field test at 90% VO2max. The TSI in vastus lateralis was monitored with near-infrared spectroscopy. The TSI remained steady between 20 and 80% of TTE. Between 80 and 100% of TTE (7.5 ± 6.1%, p < 0.05), a significant drop in TSI concomitant with a minute ventilation increase (16 ± 10 l min−1) was observed. Moreover, the increase of ventilation was correlated to the drop in TSI (r = 0.70, p < 0.05). Additionally, respiratory muscle endurance was significantly correlated to TSI time plateau (20–80% TTE) (r = 0.83, p < 0.05) and to TTE (r = 0.95, p < 0.001). The results of the present study show that the tissue oxygen saturation plateau might be affected by ventilatory work and that respiratory muscle endurance could be considered as a determinant of performance during heavy exercise.