Eccentric Isokinetic Rehabilitation for Chronic Lateral Epicondylitis in Female Swimmers: A Randomized Controlled Trial of Bilateral Neuromuscular Adaptations and Functional Performance

<i>Background and Objectives</i>: This study investigated the efficacy of eccentric isokinetic muscle strengthening versus passive motion protocols on neuromuscular function and performance capacity in female swimmers with chronic lateral epicondylitis. <i>Materials and Methods</i>: Twenty-five swimmers (age 46.1 ± 3.1 years) with lateral epicondylitis exceeding three months' duration completed a randomized controlled trial comparing eccentric training in Controlled Active Motion mode (experimental group (EG), <i>n</i> = 13) against passive motion in Continuous Passive Motion mode (control group (CG), <i>n</i> = 12). Both groups performed 18 supervised sessions over six weeks (60°/s angular velocity, progressive loading 1-12 sets × 5 repetitions). Bilateral concentric peak torque of elbow extensors and flexors constituted the primary outcomes. Secondary measures included push-up performance, explosive power assessed by the Seated Medicine Ball Chest Push Test, and goniometric range of motion. Linear mixed-effects models and analysis of covariance with baseline adjustment were employed. <i>Results</i>: Eccentric training produced side-specific strength adaptations in elbow flexors (confirmed interaction: F_1,23 = 8.56, <i>p</i> = 0.008, <i>η</i>_p² = 0.271), with the experimental group demonstrating balanced bilateral gains, whereas the control group exhibited asymmetric responses favoring the non-dominant limb. EG demonstrated superior functional gains: push-up repetitions increased 4.15 ± 1.77 versus 2.17 ± 1.27 in CG (adjusted difference = 3.21 repetitions, 95% CI [1.52, 4.90], <i>p</i> = 0.001, <i>d</i> = 1.31), while explosive power improved 0.32 ± 0.09 m versus 0.10 ± 0.06 m (adjusted difference = 0.35 m, 95% CI [0.25, 0.45], <i>p</i> < 0.001, <i>d</i> = 1.20). Range of motion remained unchanged across groups (all <i>p</i> > 0.65). <i>Conclusions</i>: Eccentric isokinetic strengthening confers substantial advantages over passive motion protocols for restoring upper-body muscular endurance and ballistic force production in swimmers with lateral epicondylitis, supporting its integration into rehabilitation frameworks for the management of tendinopathy.