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Background: There is no clear evidence whether inspiratory muscle strength (Pi_max) is closely linked to inspiratory muscle endurance (T_lim). Moreover, normal values of T_lim, measured by flow-resistive loads, have not been established. Objectives: We tried to find answers to the following questions: Is it possible to establish normative values of T_lim when using flow-dependent, resistive loads? Are Pi_max and Borg scale values predictors of T_lim? Are anthropometric and spirometric data closely related to T_lim? Is it really necessary to measure T_lim in addition to Pi_max when evaluating inspiratory muscle function? Methods: Sixty-eight healthy Austrian volunteers between 17 and 75 years of age and with a sedentary lifestyle participated in our study. Pi_max was defined as the maximal inspiratory mouth pressure, measured with a differential pressure transducer. T_lim was determined as the time span until exhaustion, while breathing against a resistive loading device. Results: Pi_max values showed a low intra- and high interindividual variability for both sexes and were significantly age, weight and height dependent. For male subjects, Pi_max was also significantly related to spirometric parameters. T_lim values showed a very high interindividual variability, but a low intraindividual variability. Interestingly, no correlation was found between T_lim and Pi_max, nor lung function parameters and age. Conclusions: The results indicate that both Pi_max and T_lim have to be determined when inspiratory muscle function is measured. Normal values for T_lim, evaluated by flow-resistive loads, cannot be satisfactorily established due to the high interindividual variability.

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