Effects of aquatic therapy vs. standard care on gluteal muscle morphology and function in individuals with chronic low back pain: a randomized controlled trial

Muscular dysfunction of the lumbar-pelvic-hip complex is a hallmark of chronic low back pain (cLBP). This dysfunction is partly driven by muscle morphometry and composition, highlighting their importance in cLBP. Exercise-based interventions are commonly used in cLBP management; however, the extent to which different therapeutic approaches influence gluteal muscle health remains unclear. Aquatic therapy may offer a distinct therapeutic environment by reducing spinal loading while facilitating progressive muscle activation. This study aimed to (1) investigate the effects of aquatic therapy (AT) versus standard care (SC) on gluteal muscle size, intramuscular fat (IMF) and strength in patients with cLBP and (2) investigate whether positive changes in gluteal muscle health (i.e., size, composition, strength) are associated with concomitant improvements in patient-oriented outcomes. This randomized controlled trial included 34 participants with moderate-to-severe cLBP. The participants were randomized to either AT (n = 18) or SC (n = 16). Both groups completed a 10-week supervised intervention program consisting of 2 sessions per week. The baseline and postintervention assessments included pelvic magnetic resonance imaging, gluteal strength testing, and patient-reported questionnaires. Changes in muscle-related and patient-oriented outcomes within and between groups were analyzed using repeated-measures analysis of covariance, with baseline disability as a covariate. Repeated measures analysis of covariance revealed no significant changes in gluteal muscle volume in either group. Significant decreases in IMF were observed in the gluteus maximus (-2.56 [95%CI: -4.47 to -0.64], p = 0.01) and gluteus medius (-1.00 [95%CI: -1.97 to -0.04], p = 0.04) in the AT group, with no significant changes in the SC group. Both groups demonstrated significant increases in gluteal maximus (AT:55.20 [95%CI: 31.84 to 78.55], p < 0.001; SC:41.45 [95%CI: 16.52 to 66.38], p = 0.002) and medius (AT:72.34 [95%CI: 44.62 to 100.05], p < 0.001; SC:43.91 [95%CI: 14.32 to 73.49], p = 0.005) strength. Improvements in gluteus IMF were moderately correlated with increases in physical quality of life (gluteus maximus: r=-0.33; gluteus medius: r=-0.31) and decreases in pain catastrophizing (gluteus minimus: r = 0.39). The AT group demonstrated significant improvements in strength and IMF content, suggesting potential musculoskeletal benefits health in individuals with cLBP. This study was registered at ClinicalTrials.gov (NCT05823857 on 10/04/2023).