The effect of breathing frequency on inspiratory muscle endurance during incremental threshold loading.

We tested whether there were differences in measures of respiratory muscle endurance between tests with spontaneously chosen breathing patterns and tests with fixed breathing rates in normal volunteers. Measures of respiratory muscle endurance-maximum load tolerated, mean mouth pressure at maximum load and peak pressure at maximum load were reproducible over three tests with the spontaneously chosen breathing pattern. There was no difference in these measurements between the three tests with fixed breathing frequency. There was no difference in tidal volume, inspiratory time, and the ratio of inspiratory time to total breath duration between the tests in which breathing pattern was spontaneously chosen; there was a difference in these measurements between the tests with a fixed breathing frequency. We conclude that regulation of breathing frequency is unnecessary in the two-minute threshold loading test to obtain reproducible results for measures of respiratory muscle endurance.