## 1 Introduction  
Change of direction (COD) is a fundamental aspect of agility, characterized by the ability to decelerate, alter the direction of movement, and then reaccelerate towards a new target [1]. While agility as a whole is heavily influenced by cognitive processes, COD specifically emphasizes the physical components of agility, without requiring a reaction to an external stimulus [2]. COD has been extensively studied across athlete populations and found to be important in a wide range of sports [3]. For example, changing direction using quick accelerations and decelerations (>2 m/s\({}^{2}\)) is found to contribute to soccer players' performance significantly [4]. Similarly, in basketball, the ability to rapidly change direction is crucial for on-court performance [5], with athletes typically executing 50-60 shifts and CODs in an average game [6].  
Strength and conditioning practitioners are continually seeking the most effective training methods for enhancing athletes' COD performance. Previous studies have adopted different types of training methods to improve COD, including strength training (ST), polyometric training (PT), complex ascending training (AT), and complex descending training (DT) [7, 8, 9, 10]. Traditional heavy-resistance strength training leads to gains in maximal strength and power mainly by targeting the force component of the power equation (i.e., power as a function of force and velocity) [11]. However, they do not play a meaningful role in maximal power improvements after one's maximal level of strength is attained [12]. Conversely, research has indicated that utilizing lighter loads in glyometric and ballistic/power exercises enables athletes to achieve greater movement velocities. This, in turn, stimulates specific neural adaptations that enhance the rate of force development (RFD) and boost maximal power output [12].  
Complex Contrast Training (CNT) has recently emerged as a training method that aims to improve COD performance [13, 14, 15, 16]. However, discrepancies exist in the terminology used to describe these methods [17]. Based on the literature, CNT is described as a training method that alternates between high-load weight exercises and lighter-load power exercises in a set-for-set manner (e.g., pairing squats with countermovement jumps) [18, 19, 20]. Complex Descending Training (DT) follows a sequential approach, beginning with high-load strength exercises and then transitioning to lighter-load power exercises [17, 21]. Conversely, Complex Ascending Training (AT) reverses this order by starting with lighter-load power exercises and concluding with high-load strength exercises [14, 17, 22]. If a study labeled the training intervention as AT, but it actually met the criteria for CNT according to our definition, we coded the training method based on our criteria rather than those used in the original article. Several studies have found that CNT could be a promising training method to improve COD, compared to power training or heavy-resistance training alone [8, 15, 23]. However, other studies revealed no difference between CNT and other training methods (i.e., strength or glyometric training) [13, 14, 24]. In sum, the potential gains from CNT compared to other training methods remain inconclusive.  
This study is the first meta-analysis to systematically synthesize and quantify existing evidence regarding the effectiveness of CNT on improving COD performance among team-sport athletes. It goes beyond a narrative review to provide quantitative estimates and compares CNT with other training methods (i.e., PT, ST, DT, and AT) using meta-analysis. This study also explored possible factors that might alter the effectiveness of CNT intervention through subgroup analyses. Findings from this review may help determine the optimal training method for improving COD among team-sport athletes.