Inspiratory muscle performance in endurance athletes and sedentary subjects

Objective: The aim of this study was to determine whether whole-body endurance training is associated with increased respiratory muscle strength and endurance. Methodology: Respiratory muscle strength (maximum inspiratory pressure (PI_max)) and endurance (progressive threshold loading of the inspiratory muscles) were measured in six marathon runners and six sedentary subjects. Results: PI_max was similar between the two groups of subjects but the maximum threshold pressure achieved was greater in marathon runners (90 ± 8 vs 78 ± 10% of PI_max, respectively, mean ± SD, P < 0.05). During progressive threshold loading, marathon runners breathed with lower frequency, higher tidal volume, and longer inspiratory and expiratory time. At maximum threshold pressure, marathon runners had lower arterial O₂ saturation, but perceived effort (Borg scale) was maximal in both groups. Efficiency of the respiratory muscles was similar in both groups being 2.0 ± 1.7% and 2.3 ± 1.8% for marathon runners and sedentary subjects, respectively. Conclusions: The apparent increase in respiratory muscle endurance of athletes was a consequence of a difference in the breathing pattern adopted during loaded breathing rather than respiratory muscle strength or efficiency. This implies that sensory rather than respiratory muscle conditioning may be an important mechanism by which whole-body endurance is increased.