The effects of respiratory muscle functions on trunk muscle endurance in healthy young adults

Purpose: Respiratory muscles play a dual role in breathing and trunk stability during activities. The relationship between respiratory muscle functions and trunk stability has not yet been clarified. The aim of the study was to examine the effects of respiratory muscle functions on trunk muscle endurance in healthy young adults. Methods: McGill's trunk muscle endurance tests, which consist of trunk flexion endurance test (FE), Sorensen test (ST) and Side Bridge test (SB), were used to evaluate the participants' trunk muscle endurance. Respiratory muscle strength was evaluated by measuring intraoral maximal inspiratory and expiratory pressures using an intraoral pressure meter device. The respiratory muscle endurance test was performed with the incremental threshold load protocol using a threshold IMT device. Results: A total of 51 healthy young adults, with a mean age of 21.8 ± 3.2 years, were evaluated. The results of the linear regression models were significantly explained 46% of the variance in the SB and 38% in the FE, (for SB Adj R2=0.46, F=21.40, p< 0.001 and for FE Adj R2=0.38, F=15.65, p< 0.001). Respiratory muscle endurance contributed 30% to the endurance of the trunk flexor muscles, while respiratory muscle strength contributed only 8%. Similarly, respiratory muscle endurance contributed 38% to the endurance of the trunk lateral flexor muscles, while respiratory muscle strength contributed only 8%. Conclusion: Although respiratory muscle strength and respiratory muscle endurance were independent contributors to trunk muscle endurance, respiratory muscle endurance more affected trunk muscle endurance than respiratory muscle strength in healthy young adults.