Identifying the Effects of Unilateral and Bilateral Complex Training on the Maximum Strength, Explosive Power, and Changing Direction Ability of Volleyball Players

Background. Unilateral and bilateral complex trainings are techniques that combine various exercises focused on developing different muscle groups and physical qualities, such as strength, power, speed, and balance. Understanding the most effective training strategy is essential for optimizing volleyball-specific physical performance. Objectives. This study aimed to compare the effects of unilateral and bilateral complex training on lower-limb performance, specifically maximum strength, explosive power, and change-of-direction ability, in male collegiate volleyball players, and to evaluate these effects within this specific group. Materials and methods. A total of 68 male volleyball players aged 18-26 years from four universities in Shanghai were randomly assigned to unilateral (n = 34) or bilateral (n = 34) training groups. Both groups underwent 8 weeks of complex training programs designed based on expert input. Performance outcomes included 1RM squat, isometric mid-thigh pull (IMTP), countermovement jump (CMJ), drop jump (DJ), 5m and 10m sprints, and agility tests. Data were analyzed using paired and independent sample t-tests and Cohen’s d for effect sizes. Results. Both training protocols significantly improved all performance indicators (p < 0.05 or p < 0.01). The unilateral group showed substantially greater enhancements in unilateral IMTP, single-leg CMJ and DJ, and short-distance sprint times. The bilateral group had better bilateral CMJ gains and slightly higher ball speed, though only bilateral CMJ reached statistical significance. No marked difference was found in change-of-direction ability, though unilateral training yielded slightly greater progress. Conclusions. The findings indicate that both unilateral and bilateral complex training are effective for enhancing lower-limb performance. However, unilateral training may be more beneficial for improving single-leg power and sprinting, while bilateral training better supports bilateral explosive strength and volleyball-specific skills.