Effects of Isolated Eccentric Squat Training at Different Velocities on Countermovement Jump Performance, Quadriceps Function, and Hypertrophy

Abstract Soda, N and Shimokochi, Y. Effects of isolated eccentric squat training at different velocities on countermovement jump performance, quadriceps function, and hypertrophy. J Strength Cond Res XX(X): 000–000, 2026—Eccentric training is widely combined with traditional resistance training to improve athletic performance. However, evidence on isolated eccentric training with free weights remains limited. This study investigated the effects of an isolated eccentric squat training at different velocities on quadriceps function, hypertrophy, and the countermovement jump (CMJ) biomechanics. Twenty-four male college students without strength training experience were assigned to 1 of 3 8-week protocols (3 sessions·wk −1 ): slow eccentric squat (SES), CMJ-specific fast eccentric squat (CMJ-specific-FES), or weighted CMJ (WCMJ) training. The SES group performed 5-second descent squats at back squat 1RM (BSQ1RM); CMJ-specific-FES used rapid descents at 50% BSQ1RM. The WCMJ group trained with loads optimized for maximal power. Quadriceps function, hypertrophy, and 3-dimensional CMJ biomechanics were assessed pre-, mid-, and postintervention. The SES group exhibited the greatest quadriceps hypertrophy (10.7% vs. −0.3–2.5%, p < 0.05–0.1), whereas the CMJ-specific-FES group showed the largest improvement in early phase quadriceps rate of force development, particularly within 25 milliseconds (104.7% vs. −20.1–18.1%, p < 0.01), despite comparable strength gains across groups (9.8–23%, p < 0.05). All groups improved CMJ height and related biomechanical variables; however, the CMJ-specific-FES group demonstrated greater increases in quadriceps activities (38.5–59.6% vs. −16.8–21.2%, p < 0.05–0.1), knee joint positive power (26.4 vs. 7.7%, p < 0.05), and CMJ height (9.6 vs. 0.9%, p < 0.05) than the SES group. These findings suggest eccentric training modes should be tailored to specific goals, such as hypertrophy or explosive power, to achieve optimal training adaptations.