The physical performance of volleyball players is significantly influenced by their jumping ability, encompassing both vertical movements (e.g., spike and serve jumps) and horizontal jumps (e.g., block jumps). While vertical jumps are crucial for attacking and blocking, horizontal jumps are essential for defensive maneuvers and court coverage (Pisa et al., 2022). Additionally, muscular strength and power are crucial for players to achieve optimal force production during spiking and serving in a match (Oliveira et al., 2025). Players in a volleyball match usually perform over 150 jumps, highlighting the importance of explosive muscular power, strength, and anaerobic power in improving scoring actions such as spiking, blocking, and serving (Silva et al., 2019; Ning and Sheykhlouvand, 2025). Therefore, it is crucial to employ appropriate training techniques that not only enhance the physical performance (i.e., strength, speed, and jumping ability) but also improve the anaerobic power output in volleyball players.

Although there are various training methods recommended for volleyball players, such as strength training (Keoliya et al., 2024; Arazi et al., 2018), sprint interval training (Tao et al., 2024; Kaynak et al., 2017), and complex training (Wang et al., 2023), recent review and experimental studies indicated that plyometric jump training (PJT) is an effective training modality to enhance jumping ability, sprint performance, anaerobic power output, and muscular strength for young male and female volleyball players with different fitness levels (Silva et al., 2019; Ramirez-Campillo et al., 2020; 2021; Hernandez-Martinez et al., 2023). PJT is a form of neuromuscular training designed to enhance explosive power by improving the ability of the muscle–tendon unit to rapidly produce force (Junior and Pinillo, 2025; Ramirez-Campillo et al., 2020; Chu, 1998). It involves a repetitive sequence of movements in which each cycle includes a rapid deceleration of the body (eccentric phase), immediately followed by a brief transition phase (amortization phase), and a rapid acceleration in the opposite direction (concentric phase) (Junior and Pinillo, 2025; Silva et al., 2019; Chu, 1998). This rapid coupling of eccentric and concentric muscle actions engages the stretch-shortening cycle (SSC), whereby elastic energy storage and neural reflex activation during the eccentric phase enhance force production during the subsequent concentric action (Chu, 1998), ultimately leading to improvements in lower-body physical performance in athletes (Ramirez-Campillo et al., 2021).

To create an appropriate PJT program, it is crucial to take into account several variables, including the number of sets, repetitions, intensity, types of exercises, rest durations, and the training surface (Saez de Villarreal et al., 2009; 2010). Nevertheless, a crucial factor that has been overlooked in previous research is the role of additional loads, such as dumbbells, barbells, or weighted vests, during the jump training. In fact, implementation of external loads has been suggested as an effective strategy in PJT to enhance anaerobic power output as well as physical performance in players (Stankovic et al., 2025; Iranpour et al., 2025; Ali et al., 2024; Khlifa et al., 2010; Kobal et al., 2017; Kang, 2018; Freitas-Junior et al., 2019; Aloui et al., 2020; Aloui et al., 2021; Gaamouri et al., 2023; Novak et al., 2023). Although PJT is traditionally performed using body weight alone (Ramirez-Campillo et al., 2020; Hernandez-Martinez et al., 2023; Saez de Villarreal et al., 2010), previous studies demonstrated that incorporating external loads, such as weighted vests (WV) (Ali et al., 2024; Khlifa et al., 2010; Kobal et al., 2017) or elastic bands (EB) (Stankovic et al., 2025; Aloui et al., 2020; Aloui et al.,2021), during the PJT can enhance neuromuscular properties and potentially greater physical performance adaptations.

The utilization of a WV during PJT can increase the eccentric load on the lower extremities, potentially leading to enhanced neuromuscular adaptations and an increased internal training load (Iranpour et al., 2025; Ali et al., 2024; Kang, 2018). Eccentric muscle actions, such as the lowering phase of a jump, generate force while lengthening, and an increased eccentric load places greater demands on muscle fibers and the surrounding connective tissues (Chu, 1998). This stimulus drives adaptations including increased muscle stiffness, improved force-conversion efficiency, and enhanced muscle damage leading to subsequent repair and hypertrophy (Ali et al., 2024). Furthermore, the incorporation of WV in PJT has been shown to elicit greater neuromuscular adaptations and enhanced physical performance compared to training without added loads (Iranpour et al., 2025; Khlifa et al., 2010). Unlike WV, EB offer an alternative method of loading during PJT by providing variable resistance across the range of motion. Specifically, EB resistance increases progressively as the elastic bands elongate during the early-to-mid concentric phase of the jump, when joint angular velocities are rising and force and power demands are near their peak. As the movement approaches full hip, knee, and ankle extension at take-off, band elongation reaches its maximum and subsequently decreases, resulting in a reduction in elastic tension and external resistance toward the end of the concentric phase (Stankovic et al., 2025). This variable resistance profile can meaningfully influence the SSC and the rate of force development, thereby promoting improvements in reactive strength and jump performance (Stankovic et al., 2025; Aloui et al., 2020). By progressively increasing mechanical demands across the range of motion, EB loading provides an enhanced stimulus to the neuromuscular system, particularly by augmenting motor unit recruitment and rate coding, which are key mechanisms underlying explosive performance adaptations (Stankovic et al., 2025; Aloui et al., 2021). Additionally, incorporating elastic resistance during training sessions not only enhances the eccentric stimulus but also increases myoelectric activity in the relevant musculature (Aloui et al., 2020). This heightened myoelectric activity contributes to enhanced adaptive responses and improved physical performance, specifically in areas such as jumping, sprinting, change of direction speed, and strength (Gaamouri et al., 2023). Therefore, we can utilize two strategies to incorporate additional loads: (a) maintaining a constant load with PJT using the WV determined by a percentage of body mass (e.g., 10% of body mass) (Kang, 2018), or (b) variable loads using EB during PJT to ensure consistent loading throughout the range of motion (Gaamouri et al., 2023).

Some suggestions have been made regarding the limited effectiveness of WV in stimulating the neuromuscular system during exercises with an ascending strength curve (Kang, 2018). During these exercises, the force produced by the involved muscle groups generally increases throughout the concentric phase of the movement, peaking near the end of the range of motion (Khlifa et al., 2010; Kobal et al., 2017). Conversely, when using EB, the load appears to be distributed more evenly throughout the entire range of motion of the exercise (Aloui et al., 2021). There is a suggestion that EB may have an advantage in facilitating muscles to produce near-maximal force throughout the range of motion (Gaamouri et al., 2023). However, further longitudinal research is necessary to gain a complete understanding of the role of WV versus EB in relation to the incorporation of added loads in PJT programs to clarify the promising suggestions.

To date, there have been no studies that have specifically examined the effects of using WV versus EB during PJT on the physical performance of volleyball players. Additionally, the superiority of each additional load strategy during PJT on physical and physiological performance adaptations for male volleyball players remains unknown. Therefore, this study aimed to investigate two main aspects: (a) the effects of PJT on the physical and physiological performance (i.e., jumping ability, sprint and change of direction speed, muscular strength, reactive strength index, and anaerobic power output) of volleyball players, and (b) the comparison between two different loading strategies—WV (constant load) and EB (variable load)—in maximizing training adaptations in male volleyball players. We hypothesized that PJT could be an effective training modality for enhancing physical performance, specifically in areas such as jumping, sprinting, change of direction speed, and strength, assuming that the inclusion of extra loads during PJT would provide additional benefits in terms of neuromuscular adaptations, ultimately leading to greater gains in physical performance for volleyball players.

All players fully complied with the research protocol, achieving a 100% success rate. Moreover, there were no recorded instances of injuries related to the training and assessment methods. Additionally, no statistically significant differences (p > 0.05) were noted between the groups during the initial assessment in anthropometric variables as well as physical and physiological performance. No significant changes were identified in the CG across any physical and physiological variables in the post-assessment. A significant group-by-time interaction (p = 0.001) was found in all physical and physiological measures, indicating that the training groups (WV-PJT, EB-PJT, and UL-PJT) showed more gains than the CG after the training period. These differences highlight that an 8-week volleyball training program alone is not sufficient to elicit improvements in these variables, and further demonstrate that the specific training methods employed in the WV-PJT, EB-PJT, and UL-PJT groups yielded greater improvements compared to the CG.

There was significant group × time interaction which indicates greater adaptive changes for the WV-PJT and EB-PJT groups than for the UL-PJT group in the CMVJ (ES = 1.60 and 1.78 vs. 1.07, p = 0.007) (Figure 2), 10-m sprint (ES = −1.40 and −1.31 vs. −0.72, p = 0.009) (Figure 3), T-CODS (ES = −1.44 and −1.54 vs. −1.02, p = 0.001) (Figure 4), RSI (ES = 1.21 and 1.38 vs. 0.62, p = 0.021) (Figure 5), 1RM_LP (ES = 1.83 and 1.17 vs. 0.90, p = 0.001) (Figure 6), peak (ES = 1.19 and 1.38 vs. 0.62,p = 0.001) (Figure 7A), and mean (ES = 0.68 and 0.87 vs. 0.41, p = 0.002) (Figure 7B) power output, respectively, following the training period.

There was no significant (p < 0.05) group by time interaction between the WV-PJT and EB-PJT in the CMVJ (p = 0.547), 10-m sprint (p = 0.855) and T-CODS (p = 0.341); however, in the 1RM_LP the WV-PJT indicated greater adaptive responses (p = 0.011, 12.1% ± 2.6% vs. 9.2% ± 1.1%, standard mean difference [SMD] = 0.51, 95% CI = −0.51–1.48) than the EB-PJT after an 8-week training intervention period (Table 3). Likewise, the EB-PJT group demonstrated greater adaptations in the RSI (p = 0.041, 21.3% ± 8.8% vs. 15.5% ± 6.4%, SMD = 0.46, 95% CI = −0.53–1.45), peak (p = 0.006, 12.2% ± 1.9% vs. 8.4% ± 1.3%, SMD = 0.49, 95% CI = −0.53–1.46) and mean (p = 0.017, 9.1% ± 1.6% vs. 6.3% ± 1.9%, SMD = 0.33, 95% CI = −0.67–1.30) power output than the WV-PJT after training intervention.

This study aimed to investigate two main aspects: (a) the effects of PJT on the physical and physiological performance of volleyball players, and (b) the comparison between two different loading strategies—WV (constant load) and EB (variable load)—in maximizing training adaptations in male volleyball players. The main findings indicated that PJT is an effective training method for enhancing physical and physiological performance compared with a CG that only performed volleyball-specific training. Moreover, both loaded PJT conditions (WV-PJT and EB-PJT) elicited greater adaptations than UL-PJT across most measured variables. Specifically, WV-PJT was more effective for improving maximal strength, whereas EB-PJT induced superior improvements in RSI, peak and mean power outputs.

Previous experimental and review studies have consistently demonstrated that bio-motor abilities such as CMVJ, 10 m sprint, and change-of-direction speed can be significantly enhanced following PJT interventions lasting 6–10 weeks in trained and young volleyball athletes (Silva et al., 2019; Ramirez-Campillo et al., 2020; Hernandez-Martinez et al., 2023). These adaptations are primarily attributed to neuromuscular mechanisms, including increased neural drive to agonist muscles, enhanced motor unit recruitment and firing frequency, improvements in inter- and intramuscular coordination, and favorable modifications in muscle–tendon unit stiffness (Saez de Villarreal et al., 2009; Silva et al., 2019). In addition, structural adaptations such as increases in muscle cross-sectional area and alterations in muscle architecture (e.g., pennation angle and fascicle length) may further contribute to improvements in force and power production (Chu, 1998; Wang et al., 2023). The observed improvements in CMVJ performance may also partially explain the concurrent enhancements in sprint and change-of-direction abilities, as vertical force production capacity has been shown to be strongly associated with horizontal acceleration and directional changes in volleyball players (Ramirez-Campillo et al., 2021; Arazi et al., 2018).

Importantly, the present findings indicate that incorporating additional external loads during PJT—via either WV or EB—elicits greater adaptations than unloaded PJT alone, which is consistent with previous interventions conducted in trained athletes over six to 8 weeks (Freitas-Junior et al., 2019; Aloui et al., 2020). From a physiological perspective, loaded PJT likely enhances the capacity of the muscle–tendon unit to store elastic energy during the rapid eccentric loading phase of the SSC and to reutilize this stored energy during the subsequent concentric phase, thereby augmenting concentric force and power output (Aloui et al., 2021). Furthermore, higher internal mechanical loads imposed on the lower-limb musculature may increase recruitment of fast-twitch motor units and elevate the mechanical stimulus required for additional neuromuscular adaptations, ultimately resulting in greater improvements in CMVJ, sprint, and change-of-direction performance (Khlifa et al., 2010).

Given the importance of minimizing ground contact time and optimizing take-off efficiency in volleyball-specific movements (Wagner et al., 2009), RSI represents a sensitive indicator of SSC function and explosive performance. The present study demonstrated that PJT significantly improved RSI, which aligns with previous systematic reviews and experimental studies reporting meaningful RSI gains following 6–10 weeks of PJT in trained populations (Ramirez-Campillo et al., 2018; Rebelo et al., 2022). These improvements are largely explained by neuromuscular adaptations that enhance the rapid transition from eccentric to concentric muscle actions, including increased pre-activation of muscles, enhanced stretch reflex sensitivity, improved musculotendinous stiffness, and greater rate of force development (Chu, 1998; Ramirez-Campillo et al., 2021; Silva et al., 2019). From a motor learning perspective, the high specificity of plyometric drills—performed with maximal intent and short contact times—likely facilitates efficient transfer to RSI performance by reinforcing task-specific neuromuscular patterns (Stone et al., 2002; Davies et al., 2015).

When comparing loading strategies, both WV-PJT and EB-PJT induced greater RSI improvements than UL-PJT, supporting the notion that additional external loading further enhances SSC efficiency and neuromuscular demand (Kang, 2018; Aloui et al., 2021). Interestingly, EB-PJT resulted in superior RSI adaptations compared with WV-PJT after the 8-week intervention. This finding may be attributed to the variable resistance profile of elastic bands, which progressively increases load throughout the range of motion, thereby intensifying eccentric–concentric coupling and neuromuscular activation (Stankovic et al., 2025; Aloui et al., 2020). Studies using variable resistance have reported greater motor unit recruitment, enhanced rate coding, and increased myoelectric activity compared with constant loads, suggesting a heightened neuromuscular stimulus (Ali et al., 2024; Iranpour et al., 2025; Gaamouri et al., 2023). Nevertheless, as neuromuscular activity was not directly assessed, these interpretations remain speculative and warrant confirmation in future studies incorporating electromyographic analyses.

Consistent with previous research, PJT also induced significant improvements in maximal strength performance (1RM), particularly when additional external loads were incorporated (Silva et al., 2019; Saez de Villarreal et al., 2010). Both WV-PJT and EB-PJT elicited greater strength gains than UL-PJT, likely due to enhanced neural adaptations such as increased motor unit firing frequency, improved synchronization, reduced antagonist co-activation, and heightened neural drive (Saez de Villarreal et al., 2009; Saez de Villarreal et al.,2010). Moreover, musculoskeletal adaptations—including muscle hypertrophy and a shift toward type II muscle fiber characteristics—may further contribute to strength development following loaded PJT (Davies et al., 2015; Arntz et al., 2022).

Notably, WV-PJT resulted in superior improvements in 1RM compared with EB-PJT. This finding may be explained by the overload principle, whereby the constant external load provided by WV enables athletes to generate higher vertical ground reaction forces over a longer portion of the concentric phase during jump tasks (Khlifa et al., 2010). This sustained force application increases net impulse, which likely promotes force-oriented mechanical adaptations and, consequently, greater improvements in maximal strength compared with variable loading conditions (Freitas Junior et al., 2019).

A novel contribution of the present study is the examination of anaerobic power responses to loaded PJT using WV and EB. The findings demonstrated moderate to large improvements in peak and mean power output following PJT, particularly under loaded conditions, with EB PJT eliciting greater gains than WV PJT. Previous research indicates that PJT enhances anaerobic power primarily through neuromuscular mechanisms, including greater recruitment of high-threshold motor units, increased firing rates, and improved efficiency of the phosphagen system (Malisoux et al., 2006; Markovic and Mikulic, 2010; Song and Sheykhlouvand, 2024). Collectively, these adaptations contribute to improvements in peak and mean power output. The superior anaerobic power adaptations observed following EB PJT may be attributed to the greater metabolic and neuromuscular demands imposed by variable resistance throughout the range of motion (Aloui et al., 2020). This loading profile may provide a more effective stimulus to peripheral metabolic pathways, potentially enhancing phosphagen system efficiency, metabolite clearance, and the maintenance of ATP and PCr stores during high-intensity efforts (Stankovic et al., 2025; de Poli et al., 2021; Gaamouri et al., 2023; Gharaat et al., 2020; Li and Sheykhlouvand, 2025; Forbes and Sheykhlouvand, 2016). However, as metabolic and neuromuscular variables were not directly assessed in the present study, these proposed mechanisms remain speculative and should be confirmed in future investigations.

Despite the practical relevance of these findings, several limitations should be acknowledged. The relatively small sample size (n = 8 per group) may limit generalizability, although an a priori power analysis indicated sufficient statistical power (Freitas-Junior et al., 2019). Additionally, the exclusive inclusion of male volleyball players restricts extrapolation to female athletes or other sports populations. The absence of direct assessments of neuromuscular (e.g., EMG) and metabolic adaptations further limits mechanistic interpretation. Importantly, although improvements were observed in physical and physiological performance, the transfer of these adaptations to actual competitive volleyball performance remains uncertain due to the lack of systematic match or time-motion analysis. Future studies incorporating match-based performance indicators and biomechanical monitoring are required to clarify the ecological validity of PJT-induced adaptations.

The findings of this study indicate that integrating an 8-week PJT program, performed three times per week in conjunction with regular technical–tactical volleyball training, effectively enhances physical performance and anaerobic power output in male volleyball players. Notably, PJT performed with additional external loads elicited superior adaptations compared with unloaded PJT. Specifically, the WV-PJT was more effective for improving maximal strength, whereas EB-PJT produced greater enhancements in RSI and anaerobic power output. Practically, both WV and EB loading strategies can be periodized within a season according to specific performance objectives, athlete readiness, and training phase. Overall, the use of loaded PJT represents an effective, time-efficient, and sport-specific approach for improving bio-motor abilities and anaerobic performance in male volleyball players. From a practical perspective, coaches and practitioners are encouraged to incorporate loaded PJT into volleyball training programs to optimize performance adaptations. During phases in which maximal strength development is prioritized (e.g., early pre-season or strength-oriented mesocycles), WV-PJT appears to be the most appropriate strategy. Conversely, when the primary goal is to enhance explosive qualities requiring rapid force production, such as RSI and anaerobic power (e.g., late pre-season or competitive phases), EB-PJT may be preferable.