Maximum abdominal excursion assessment using an abdominal excursion measuring device: Reliability and validity of a new device for simple and quantitative assessment of respiratory function

•The current respiratory function measurement devices are difficult to use and require specialist operations.•We devised a simple respiratory muscle assessment method, abdominal expansion measurement, which measures the amount of abdominal expansion to the ventral side.•Studies have shown that measures the amount of abdominal expansion to the ventral side is reliable and valid and helps estimate the respiratory muscles.•If further data collection and a simple measurement tool are developed, abdominal expansion measurements may become common. This study aimed to verify the reliability and validity of abdominal expansion and respiratory function measurements. Forty healthy adult males underwent lung capacity, effort lung capacity, respiratory muscle strength, cough strength, diaphragm ultrasound, and abdominal expansion measurements. Abdominal expansion was measured using a device developed to accurately evaluate abdominal movements and calculate maximum abdominal expansion on the ventral side (AE-max: the difference between maximal abdominal contraction at the same time as maximal-effort expiration and maximal abdominal expansion at the same time as maximal-effort inspiration). Intra- and inter-rater reliabilities of the AE-max measurements were examined, the paired t-test was used for assessing the ratios of the expansion and contraction displacement components in AE-max, and regression analysis was used to obtain equations for predicting maximum inspiratory pressure (MIP) based on AE-max. Both intra- and inter-rater reliabilities were high. Criterion-related validity showed that AE-max was associated with all respiratory function parameters, especially MIP, and a high percentage of expansion displacement. Regression analysis showed that AE-max was significantly associated with MIP. Based on its association with MIP, the large proportion of expansion displacement in AE-max, and the results of the multiple regression analysis, we conclude that AE-max is a helpful measure for estimating MIP.