Comparison of diaphragmatic endurance, trunk muscle endurance, and respiratory function in individuals with and without forward head posture: a case control study

Introduction Forward head posture (FHP) is a common postural disorder. The aim of this study was to compare diaphragmatic endurance, trunk muscle endurance, and respiratory function in individuals with and without forward head posture (FHP).Methods The study included individuals with (FHP group, n = 32) and without (control group, n = 35) FHP. FHP was determined by craniovertebral angle. Diaphragmatic endurance was assessed using the Maximum Phonation Time (A/I phonation test), trunk muscle endurance using McGill Trunk Endurance Muscle tests (trunk flexion endurance test, trunk extension endurance test, trunk lateral flexion endurance test), and respiratory function using spirometry. Independent Sample T-test and Mann Whitney U test were used for analysis.Results Individuals with FHP had lower mean A (p = 0.006, d = 0.69), I (p = 0.015, d = 0.61) phonation durations, and significantly all trunk muscle endurance across all tests (p < 0.001, d = 1.31–1.73) compared to control group. No significant between-group differences were found in respiratory parameters (p > 0.05).Conclusion Individuals with FHP demonstrated significantly reduced A/I phonation duration-suggestive of impaired diaphragmatic endurance and reduced trunk muscle endurance compared to individuals without FHP, while respiratory function remained similar between groups. These findings suggest that diaphragmatic and trunk muscle function should be considered in the clinical management of FHP.