## 1 Introduction  
Currently, the interest of researchers regarding eccentric muscle actions and their associated training methods has increased substantially due to their multiple benefits [1, 2, 3, 4].  
These include an increased capacity to generate force, a selective recruitment of high-threshold motor units (IIx), and a lower metabolic cost per unit of external work versus concentric and isometric actions [4; 5]. Accentuated eccentric loading (AEL) is a training method that uses eccentric loads greater than concentric loading in full stretch-shortening cycles, with minimal disruption to natural movement mechanics [4]. The magnitude of the eccentric load prescribed during AEL can be less than the concentric repetition maximum (i.e., submaximal AEL), equal to the concentric repetition maximum (maximal AEL), or greater than the concentric repetition maximum (i.e., supramaximal AEL) [6]. An example of submaximal AEL is countermovement jump (CMJ), which could be effective when prescribed with loads around 10-20% of body mass to improve muscle strength and power characteristics [3]. Conversely, maximal and supramaximal AEL have commonly been implemented using weight releases during traditional exercises such as the squat or bench press [6], with the primary goal of improving maximal strength [4; 6]. However, these approaches present practical limitations for use in sports settings due to the requirement of specific equipment [6].  
The use of submaximal AEL has been reported to produce acute improvements in vertical jump height, strength, velocity, and power [7; 8; 9; 10; 11], as well as chronic enhancements in kinetic and kinematic variables of the jump [12; 13; 14]. However, the current evidence remains partially inconsistent regarding the optimal prescription of submaximal AEL. This uncertainty arises due to heterogeneity in participants' training experience and relative strength levels, variations in exercise selection (e.g., squat vs. jump exercises), differences in load magnitude, diversity in AEL implementation methods (e.g., weight releases, dumbbells, elastic bands), and inconsistency in the performance outcomes analyzed across studies [3; 4; 6]. On the other hand, most existing studies have focused on analyzing the short-term effects of submaximal accentuated eccentric loading (AEL) through jumping exercises (i.e., immediately after or within a few days following a single or limited number of sessions) [7; 8; 9; 10; 11]. In contrast, there remains limited research investigating longer-term adaptations following multi-week submaximal AEL interventions aimed at improving physical fitness in athletes [12; 13; 14; 15]. To date, only two studies [14; 15] have examined multi-week submaximal AEL interventions using CMJ protocols. Both studies concluded that additional research is needed to optimize training parameters (e.g., frequency, volume, intensity) and to better understand the time course and magnitude of adaptations when applying AEL compared to traditional loading protocols.  
However, to our knowledge, no study has investigated the longer-term adaptations to AEL in combat sports, specifically in amateur boxers. Given the needs of boxers to increase their lower body muscle strength and power to increase the peak force of their punches [16], the inclusion of a submaximal accentuated eccentric loading jump training program could be beneficial for their performance, becoming a new training alternative for coaches and physical trainers. Therefore, this study aimed to identify the effects of a submaximal accentuated eccentric jump training program on punching performance and countermovement jump force-time characteristics in amateur boxers. Based on existing findings [3; 13; 14; 17], we hypothesized that a submaximal accentuated eccentric loading jump training program would improve punch peak force and CMJ kinetic variables to a greater extent compared to the jumping condition without AEL.