Learning effect of respiratory muscle endurance tests in healthy adults

We aimed to evaluate learning effects, feasibility, and self-reported experiences of incremental and constant load respiratory muscle endurance tests (IET/CET) in healthy subjects. PImax, handgrip force and physical activity (PA) were assessed. IET and CET were performed on 2 visits (V1 and V2) using the POWERBreathe®KH2 with a pressure threshold load. The IET started at 10%PImax. Load was increased by 10%PImax/min until task failure and peak pressure (Ppeak) was recorded. For CET this Ppeak was used as the initial load. In case of tests <3min or ˃10min, this load was adjusted to obtain an optimal test duration. Time until task failure (Tlim) was registered. 61 subjects were recruited (39±16y, 33 males). Handgrip force was 37±12kg (83±19%predicted) and 62% of subjects had a moderate PA level. PImax was 104±28cmH2O at V1 vs. 111±27cmH2O at V2 (p<0.001). Ppeak was 82±25cmH2O (78%PImax; range:15-115%) at V1 vs. 96±27cmH2O (86%PImax; range:32-130%) at V2 (p<0.001). Regarding CET, Tlim did not show significant differences between both visits (6.6±3.6min vs. 6.7±3min) but the submaximal load against which CET was performed increased significantly: 84±25cmH2O (81%PImax; range:29-121%) vs. 94±26cmH2O (84%PImax; range:23-130%); (p<0.001). During V2 only 1 subject needed a second attempt for the IET while 41 subjects needed a second attempt for the CET (20 because test duration <3min and 18 ˃10min). In 13 subjects despite the total of 4 attempts the registered CET was still ˃10min and in 3 it was still <3min. The IET was experienced as more comfortable than the CET (p<0.001) and was preferred by 75% of subjects (p<0.001). Both tests showed a large learning effect but IET was easier to perform and preferred by subjects.