Assessment of Inspiratory Muscle Endurance in Healthy Adults by Recording Breathing Characteristics

Respiratory muscle function is considered as strength and endurance. Since respiratory muscles are used a submaximally in daily life, measurement of respiratory muscle endurance rather than respiratory muscle strength is a more functional assessment. Measurement of respiratory muscle endurance is recommended to be performed by controlling the respiratory frequency and recording the breathing parameters. The purpose of this study was to evaluate respiratory muscle endurance with the incremental threshold loading (ITL) test in healthy adults by recording breathing parameters.

This observational, cross-sectional study included 112 healthy adult subjects aged between 18 to 35 years. The anthropometric characteristics (weight and height), pulmonary function testing including forced expiratory volume (FEV1), forced vital capacity (FVC), and maximal voluntary ventilation (MVV), maximum inspiratory pressure (MIP), and physical activity level (International Physical Activity Questionnaire-Short Form - IPAQ-SF) were evaluated. Inspiratory muscle endurance is assessed with ITL.

The inspiratory muscle endurance (PImax) was 54.08±21.62 cmH2O. Correlations between the PImax showed weak positive results with height (r=0.392, P < 0.001), weight (r=0.382, P < 0.001), and FEV1 (r=0.386, P < 0.001), moderate positive results with FVC (r=0.446, P < 0.001) and MVV (%) (r=0.541, P < 0.001), while strong positive results with MIP (r=0.796, P < 0.001). According to the regression analysis results, the MIP and MVV% values explained 63% of PImax.

Inspiratory muscle endurance in healthy adults can be explained with MIP and MVV. The ITL testing that is performed by recording respiratory mechanics, such as the inspiratory volume, inspiratory flow and work of breathing, can guide the determination of respiratory muscle training intensity.