en ستون فقرات Spine surgery پژوهشی Research Article <div style="text-align: justify;"><strong>Background</strong>: The gluteus medius (GMed) and quadratus lumborum (QL) muscles play crucial roles in stabilizing the pelvis and spine, yet their activation may be compromised in individuals with low back pain. Water exercises have shown promise in enhancing muscle function and coordination.&nbsp;<br> <strong>Objectives</strong>: This study aimed to investigate the effectiveness of water kinetic chain exercises in improving maximum voluntary isometric contraction (MVIC) of the targeted muscles in patients with chronic non-specific low back pain (CNSLBP).<br> <strong>Methods</strong>: A double-blind randomized controlled trial enrolled sixty men aged 40&ndash;60 years with CNSLBP. Participants were randomly assigned to three groups: water-based open kinetic chain exercises (WOKCe), water-based closed kinetic chain exercises (WCKCe), and a no-intervention control group. Surface EMG assessed MVIC, with electrodes positioned over the QL (about 2&ndash;3 cm lateral toward the L3 spinous process) during lateral trunk flexion and over the GMed (at the midpoint between the greater trochanter and the iliac crest) during hip abduction. Between-group differences were assessed using analysis of covariance (ANCOVA) after eight weeks of intervention (three sessions per week).&nbsp;<br> <strong>Results</strong>: ANCOVA revealed significant improvements in MVIC for both experimental groups compared to controls (P<0.05). For GMed MVIC, both aquatic exercise groups demonstrated significant improvements (F=7.08, P=0.002, &eta;&sup2;=0.212) with high statistical power (0.917). Similarly, for QL MVIC, both intervention groups showed substantial enhancements (F=12.94, P=0.001, &eta;&sup2;=0.316) with excellent statistical power (0.996). Post-hoc analyses confirmed that both WCKCe and WOKCe groups achieved comparable improvements in both muscle groups, with no significant differential effects between the two intervention modalities.<br> <strong>Conclusion</strong>: Both the WOKCe and WCKCe interventions resulted in significant enhancements in MVIC of the GMed QL muscles. These results suggest that either intervention can be effectively integrated into clinical and rehabilitation practices to improve muscle function and stability in individuals with chronic low back pain. This underscores the potential for tailored therapeutic strategies to optimize patient outcomes in musculoskeletal rehabilitation.</div> Low back pain, Maximum voluntary isometric contraction (MVIC), Kinetic chain, Gluteus medius (GMed), Quadratus lumborum (QL) 121 136 http://jros.iums.ac.ir/browse.php?a_code=A-10-2723-1&slc_lang=en&sid=1 Hossien Ashoury hoosienashoury@yahoo.com, h_ashoury@pnu.ac.ir 10031947532846008657 10031947532846008657 Yes Department of Physical Education and Sport Sciences, Payame Noor University, Tehran, Iran. Ali Yalfani yalfani@basu.ac.ir 10031947532846008658 10031947532846008658 No Department of Sport Rehabilitation, Faculty of Physical Education and Sport Sciences, Bu-Ali Sina University, Hamadan, Iran.