Introduction. Respiratory muscle endurance assessment methods are currently not well-standardized.

Aims. To develop standardized protocols for both incremental and constant load respiratory muscle endurance tests (IET/CET), while quantifying potential learning effects and assessing the subjective experience of participants.

Methods. A cross-sectional study was conducted in healthy non-smoking adults from Spain and Belgium. After measuring maximal respiratory pressure (PImax), IET and CET were performed on two visits with the POWERBreathe®KH2, using a threshold load. The IET started at 10%PImax. Load was subsequently increased by 10%PImax/min until task failure. The peak pressure (Ppeak) was recorded. For CET the Ppeak achieved in the IET for each visit was used as initial load. In case duration was <3 min or ?10 min, load was adjusted to achieve an optimal test duration. Time until task failure (Tlim) and subjective experience were assessed.

Results. The sample was composed of 45 subjects (37±17 years, 23 males). In 32 subjects a second attempt for the CET was required during the second visit. There was a significant learning effect observed during the IET (Ppeak:82±23cmH₂O vs. 91±26cmH₂O; p<0.001), which was also reflected in the load selected for the CET (81±25cmH₂O vs. 90±26cmH₂O; p<0.001). Tlim during CET was 7.1±2.7min vs. 5.9±2.4min on both visits (p=0.02). In general, the IET was experienced as more comfortable than the CET (p<0.001) and preferred by 78% of participants (p<0.001).

Conclusions. The proposed standardized protocols for IET and CET are feasible in healthy adults. Significant learning effects were observed and the IET was easier to perform and preferred by the volunteers.