Respiratory muscle strength and endurance in individuals with and without lumbar instability: a cross-sectional study

Purpose Lumbar instability (LI) is a common cause of mechanical low back pain. Four primary muscle groups, including the abdominal, back, respiratory, and pelvic floor muscles, contribute to lumbar stability. Although previous studies have reported reduced strength in the abdominal and back muscles among individuals with LI, respiratory muscle, which plays a crucial role in spinal stability, remains largely unexplored in this population and has not been compared across patients with chronic low back pain (CLBP) and healthy individuals. Therefore, this study aimed to examine the strength and endurance of the respiratory muscles in individuals with CLBP, those with LI, and healthy controls. Methods 120 participants who met the inclusion criteria were recruited and divided equally into three groups: healthy individuals, CLBP, and LI groups. The outcome measurements included (i) inspiratory and (ii) expiratory muscle strength, measured as maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP), both reported in cm H2O; and (iii) respiratory muscle endurance, measured as maximum voluntary ventilation (MVV) using a spirometer and reported in litres per minute (l/min). Results The results revealed that MIP in the LI group was significantly lower compared to both the CLBP group (p = 0.04) and the healthy group (p < 0.001), whereas MEP showed no significant difference across the three groups. MVV showed significant differences between the LI group and the healthy group (p-value = 0.02). Conclusions Patients with lumbar instability exhibit reduced respiratory muscle strength, highlighting the importance of identifying this subgroup and prioritising respiratory muscle training alongside core strengthening in rehabilitation.