Taekwondo is a Korean martial art that has evolved from a military combat system into a modern competitive sport. After World War II, techniques from traditional styles were consolidated into a unified method, forming the basis of the contemporary sport. Since the 1950s, Taekwondo has undergone steady modernization, culminating in official Olympic recognition in 1994 and inclusion in the Olympic Games from 2000 ([21]).

As a competitive sport, Taekwondo is characterized by frequent high-velocity kicking, rapid decision-making, and repeated explosive actions under time pressure. Performance hinges on lower limb power, inter-limb coordination, and dynamic control, and World Taekwondo (WT, formerly WTF) competition emphasizes technology-assisted scoring and sport performance, a feature that distinguishes modern WT competition formats from many other combat sports contexts ([12]). These neuromechanical demands motivate the use of standardized jump assessments, particularly the drop jump (DJ) and the reactive strength index (RSI), for performance profiling.

Lower limb strength is a primary determinant of performance in Taekwondo, supporting rapid kicking, quick jumping actions, and stance stability ([10]; [14]). In practice, performance depends on integrating strength and speed with technical and tactical skills, so explosive strength and jump-based drills are common in high-level preparation. Accordingly, short, repeated exchanges in Taekwondo rely on the alactic anaerobic (ATP-PCr) system to provide immediate power and enable rapid recovery between efforts ([5]; [6]; [19]; [25]).

From a neuromechanical perspective, lower limb actions in competition commonly reflect three transition types between muscle contraction modes: 1) isometric to concentric, 2) controlled eccentric braking followed by a fast concentric action with a longer eccentric to concentric coupling time (a slower SSC), and 3) rapid eccentric braking followed by a fast concentric action with minimal coupling time (a fast SSC) ([15]; [17]; [26]). In high-performance sports science, three jump assessments are frequently used to profile these qualities: squat jump (SJ), countermovement jump (CMJ), and drop jump (DJ). These tests are widely employed in Taekwondo training and periodic evaluations ([18]; [20]). Interventions reported in the literature have typically been short with a limited number of sessions, and elite athletes generally outperform recreational counterparts in jump metrics ([3]). Mechanistically, CMJ and DJ emphasize reactive strength via the fast SSC, whereas SJ starts from an isometric squat and minimizes SSC contribution, thereby isolating concentric force production ([7]; [16]; [24]). Prior research has shown associations between SJ/CMJ performance and speed/change-of-direction ability in Taekwondo, karate, fencing, and across elite athletes in agility-dominant sports ([8]; [9]; [13]). A DJ entails stepping off a box from a known height, contacting the ground, and immediately performing a maximal vertical rebound while minimizing ground-contact time (GCT) ([4]; [11]). The DJ is commonly evaluated alongside the RSI, calculated as jump height divided by GCT. RSI reflects an athlete’s capacity to transition rapidly from eccentric braking to concentric propulsion within a fast SSC. Because RSI is technique sensitive, valid comparisons require standardized and explicitly reported testing procedures, including drop height, hand position, arm swing, the chosen strategy (bounce or countermovement), trunk posture, footwear, surface, and timing method ([23]). Using several drop heights in DJ testing helps determine each athlete’s optimal height, where RSI is highest. When the testing procedures are standardized, the results are acceptably consistent across different days ([4]). Recent work also shows acceptable within- and between-day reliability for CMJ and DJ outcomes when familiarization, warm-up, and consistent cueing are provided, and recommends reporting indices such as the coefficient of variation and the minimal detectable change for applied monitoring ([11]). Moreover, a systematic review and meta-analysis indicate that plyometric jump training improves RSI compared with controls, underscoring RSI’s value for performance tracking ([22]).

To date, the scientific literature has not documented a short-term training program that integrates all three jump modalities (SJ, CMJ, and DJ) within a single combined jump and strength regimen for competitive Taekwondo. Accordingly, this study presents an eight-week program and quantifies short-term changes in SJ, CMJ, and DJ performance among elite competitive taekwondo athletes during the general preparation period. We hypothesized significant improvements from pre-post across all three tests, including an increase in DJ RSI that would reflect higher jump height and/or reduced GCT.

Descriptive and inferential outcomes for SJ, CMJ, and DJ are summarized in Table 1. All jump modalities showed increased height, while DJ GCT decreased (i.e., shorter/faster ground-contact time, indicating improvement), and RSI (cm/ms) increased. Test statistics and effect sizes appear in Table 1; graphical summaries are provided in Figures 1-4. Most athletes shifted toward higher iso-RSI bands, reflecting greater jump height, shorter ground-contact time, or both (Figure 3).

Across the cohort, SJ, CMJ, and DJ height increased significantly (all p < 0.001), whereas DJ GCT decreased (p= 0.040), indicating faster ground contact; consequently, DJ RSI improved markedly (p < 0.001). Effect sizes (Cohen’s d_z) were large for SJ (1.964), CMJ (2.858), DJ height (1.596), and DJ RSI (1.932), and moderate for DJ GCT (−0.757), consistent with the directionality that lower GCT reflects improvement.

Table 1. Jump outcomes pre-post (n = 10). Values are mean ± SD. Absolute change = Post − Pre; Percent change = (Post − Pre)/Pre × 100. Lower GCT indicates faster contact. RSI (cm/ms) was computed as height in centimeters divided by GCT in milliseconds. Two-tailed paired tests. Effect sizes are Cohen’s d_z = t/√n.

Abbreviations: SJ = squat jump; CMJ = countermovement jump; DJ = drop jump; GCT = ground-contact time; RSI = reactive strength index. *p < 0.05 and ***p < 0.001 indicate statistically significant pre-post differences (two-tailed paired tests; α = 0.05).

Figure 1. Pre- and post-intervention comparison of jump height (mean ± SD). SJ = squat jump; CMJ = countermovement jump; DJ = drop jump. ***p < 0.001, pre-post difference.

Figure 2. Individual pre-to-post changes in drop jump reactive strength index (RSI, cm/ms); lines connect each athlete (n = 10). Individual paired traces show that nearly all athletes improved RSI from pre-post, with modest between-subject variability. The paired-line display emphasizes consistent within-subject gains without relying on subject identifiers.

Figure 3.RSI-map showing individual PRE (●) and POST (■) values with iso-RSI reference lines (e.g., 1.6 - 2.7 cm/ms; higher = better). Lower GCT indicates faster contact; lines connect each athlete from pre-post (n = 10). Legend: Level 1 (≈1.6 cm/ms), Level 2 (≈1.8 cm/ms), Level 3 (≈2.1 cm/ms), Level 4 (≈2.4 cm/ms), Level 5 (≈2.7 cm/ms).

Figure 4. Change-change plot of ΔDJ height (cm) versus ΔGCT (ms) with iso-ΔRSI contours (cm/ms) computed around the cohort PRE mean. Leftward = shorter ground-contact (improvement); upward = higher drop-jump height (improvement). Points farther above the ΔRSI = 0 line indicate greater increases in RSI, whereas points below indicate decreases.

The present study demonstrated statistically significant short-term improvements in jump performance across all three tests (SJ, CMJ, DJ) in competitive Taekwondo athletes following an eight-week plyometric-focused mesocycle undertaken alongside coach-prescribed strength training. At the group level, SJ, CMJ, and DJ height increased, DJ GCT decreased, and DJ RSI (cm/ms) increased from pre to post, indicating enhanced ability to transition rapidly from eccentric braking to concentric propulsion within the fast SSC. These outcomes are consistent with the intended content and timing of the intervention during the general preparation period. The direction and magnitude of change broadly align with prior reports that integrated strength and plyometric training can improve explosive performance in combat-sport and elite athletic contexts (Boyanmış et al., 2024; [3]). Given that reactive metrics were available for DJ only, the concurrent increase in DJ RSI alongside shorter GCT indicates improved fast SSC execution characterized by reduced coupling time and maintained take-off intent. Accordingly, and consistent with this mechanism, the ΔDJ height-ΔGCT change-change plot and the RSI-map (Figure 3 and Figure 4) support this interpretation by showing whether athletes improved through shorter contact, greater height, or both. RSI focused interpretation. Beyond increases in jump height per se, the concurrent improvement in DJ RSI alongside a reduction in GCT indicates that athletes not only jumped higher but also did so with quicker GCT, reflecting more efficient exploitation of the fast SSC. The individual paired-line display and RSI-map visualizations (Figures 2-4) help clarify the mechanism of change by showing athlete-specific shifts upward (greater height), leftward (shorter GCT), or both, traversing to higher iso-RSI bands. This pattern aligns with meta-analytic evidence that plyometric jump training improves RSI relative to controls ([22]) and with reports that, under standardized execution and adequate familiarization, CMJ and DJ outcomes are sensitive and reliable for detecting short-term neuromuscular adaptations ([11]). Moreover, monitoring height alone can be misleading because longer contact times may inflate jump height without capturing fast-SSC efficiency. In time-pressured striking and counter-striking exchanges, faster coupling with maintained jump intent is likely performance-relevant. Accordingly, the height-to-time ratio (RSI) is the critical metric in time-pressured tasks ([4]). Finally, the need to standardize instructions and drop height is consistent with evidence that RSI is technique sensitive and varies with execution strategy ([23]).

Relative gains across tests. The largest relative improvement was observed for DJ RSI, followed by DJ height, with smaller yet clear gains in CMJ and SJ. This hierarchy is coherent with the test mechanics: CMJ and especially DJ place greater emphasis on fast SSC behavior and reactive strength, whereas SJ minimizes SSC contribution and isolates concentric force production ([7]; [24]). Together, the pattern suggests that the structured plyometric progression preferentially improved fast SSC qualities while still benefiting concentric explosive capacity.

Comparison with prior work. The magnitudes observed here are broadly comparable to improvements reported after short mesocycles in related populations, while recognizing that program length, drill selection, and loading progressions vary across studies (e.g., [3]; [6]; [9]; [18]). Importantly, RSI has emerged as a practically meaningful indicator sensitive to plyometric training, and our findings of increased RSI with reduced GCT complement meta-analytic evidence that plyometric jump training improves RSI relative to controls. In a Taekwondo-specific context, where repeated explosive actions under time pressure are central, RSI-oriented improvements are especially relevant to performance profiling and monitoring.

For coaches working with competitive Taekwondo athletes, combining a progressive plyometric block with ongoing strength work can support short-term gains in fast SSC function, as reflected by higher DJ RSI and shorter GCT. The RSI-map and change-change plots (Figure 3 and Figure 4) provide actionable diagnostics at the individual level to identify whether an athlete’s limiting factor is contact-time reduction, vertical impulse generation, or both, and to tailor technical cues and drill selection accordingly.

Context of concurrent training. Because strength sessions proceeded as part of routine, coach-prescribed practice and were not investigator-controlled, the present results should be interpreted as ecologically valid effects of a real-world plyometric mesocycle conducted alongside usual strength training rather than as isolated effects of plyometrics alone. In practical terms, it is plausible that the concurrent free-weight work increased maximal force capacity and rate of force development, while the plyometric block enhanced fast stretch-shortening cycle (SSC) behavior, yielding additive or even synergistic effects on jump height and RSI (e.g., reduced coupling time with maintained take-off intent). Mechanistically, improved neural drive, inter-muscular coordination, and muscle-tendon unit stiffness from repeated high-velocity SSC exposures can complement strength-induced gains in concentric force production, thereby supporting faster GCT and higher reactive output ([17]; [24]). Accordingly, the post-intervention pattern observed here—shorter DJ GCT with higher RSI—may reflect complementary adaptations from the combined stimulus rather than from plyometrics in isolation. At the same time, because loads, volumes, and progression of the strength sessions were not recorded, the relative contribution of each component cannot be partitioned, and causal inference should be made cautiously within this combined-practice context. This interpretation is consistent with evidence that plyometric programs preferentially improve reactive strength index ([22]) while resistance training in moderate repetition ranges (≈5 - 10 RM) targets maximal strength qualities pertinent to vertical impulse generation ([5]).

Overall, the integrated assessment of SJ, CMJ, and DJ within a single mesocycle, together with explicit RSI and GCT outcomes, supports the utility of a short-term plyometric block for enhancing reactive-strength qualities in competitive Taekwondo athletes and provides practitioners with interpretable, mechanism-linked metrics for athlete monitoring ([3]; [11]; [22]). Neuromuscular mechanisms underlying SSC improvements. The performance gains in DJ (shorter GCT with higher RSI) and the increased SJ/CMJ heights are consistent with adaptations that enhance fast stretch-shortening cycle (SSC) execution. First, increased neural drive and rate of force development (RFD) after high-velocity exposures can elevate early-phase force, aiding rapid force transmission within brief ground-contact windows. Second, improved inter-muscular coordination and motor-unit synchronization can reduce unnecessary co-activation and refine the timing of ankle-knee-hip contributions, supporting efficient energy transfer through the kinetic chain ([17]). Third, modifications in muscle-tendon unit stiffness—for example, greater tendon stiffness and/or enhanced pre-activation—can improve elastic-energy storage and return, thereby reducing coupling time and elevating reactive output ([17]). Taken together, these adaptations provide a plausible basis for the observed pattern of faster GCT with higher RSI, especially when plyometric exposures are layered on top of strength-induced increases in maximal concentric force capacity ([24]; [5]).

Potential learning and novelty effects. Although the athletes were experienced competitors, their limited prior formal practice with the specific jump modalities (SJ/CMJ/DJ) likely introduced a learning component that amplified early gains. Short-term improvements can arise from several task-specific processes: 1) familiarization with test instructions and constraints, which reduces performance variability across trials; 2) refinement of movement strategy, such as optimizing countermovement depth and timing in CMJ or minimizing coupling time in DJ; and 3) improved task-specific coordination and cueing adherence that enhance force transmission during brief ground-contact windows. We attempted to mitigate novelty by using a structured warm-up and specific rehearsal of SJ, CMJ, and DJ before testing, with standardized instructions and repeat trials; however, some portion of the observed change—particularly the larger gains in DJ RSI—may still reflect improved test execution rather than only physiological adaptation. Practically, this emphasizes the need to interpret short-term changes alongside indices of reliability and minimal detectable change and, when feasible, to include multiple baseline sessions or an extended familiarization phase. Future work should also compare athletes with established experience in these jump tasks to quantify the proportion of variance attributable to novelty.

Several limitations should be noted that may have influenced the results.

1) The study lacked a control or comparison group, which limits internal validity and prevents causal attribution to the intervention.

2) Although participants were experienced competitive athletes, they had limited prior formal practice with the specific jump modalities (SJ/CMJ/DJ), so a learning effect likely contributed to part of the short-term improvements. Although we standardized warm-up, instructions, and task rehearsal, we did not include multiple baseline sessions to fully saturate familiarization. Future studies should employ extended familiarization or repeated pre-tests and report reliability-based thresholds (for example, coefficient of variation and minimal detectable change) to better separate learning from true training effects.

3) DJ testing used a single fixed drop height (40 cm), which may not reflect each athlete’s optimal RSI height. Future research should employ an individualized drop-height protocol to identify and test at each athlete’s RSI-maximizing height, and report whether conclusions are robust across heights.

4) The concurrent, team-prescribed strength training was not investigator-controlled or logged, so working loads, intensity, set and rep structures, and session RPE were unavailable. This precluded evaluating changes in relative strength or estimating the separate contribution of strength work to outcomes.

5) The analytic sample was small (n = 10) and comprised male athletes only, which constrains statistical power and limits generalizability beyond competitive male Taekwondo athletes.

6) The intervention lasted eight weeks, so long-term effects and retention cannot be inferred.

7) Testing occurred during the general preparation period, which may limit external validity to other phases of the season, such as pre-competition or in-season.

8) There was no systematic nutritional oversight during the training period. Variability in dietary intake and recovery strategies may have contributed to inter-individual differences in adaptation.

This section reflects combined practice: the plyometric mesocycle was implemented alongside coach-prescribed strength that was not investigator-controlled or logged. Therefore, practitioners should interpret the implications in the context of concurrent plyometric and strength training rather than plyometrics in isolation.

1)Emphasize fast SSC mechanics in DJ.Coach for minimal coupling time and brief ground contact to drive RSI up. Use clear cues such as “stiff landing”, “quiet feet”, and “full intent to jump”, and ensure that technical quality is prioritized over adding external load.

2)Useweekly DJ monitoring to guide decisions.Track DJ height, GCT, and RSI once per week under standardized conditions. A weekly cadence aligns with the typical microcycle and balances sensitivity with practicality. Compare each week to an individual rolling baseline (for example, the previous 3 weeks) and to your lab’s reliability thresholds (for example, typical error and minimal detectable change).

If RSI drops beyond reliability thresholds and GCT lengthens, treat this as accumulated fatigue: reduce plyometric contacts and/or overall volume for the coming week, increase recovery between sets, and reinforce quick-coupling technique.

If height rises but GCT also rises (RSI unchanged), cue faster coupling (quiet, short contact) and prioritize drills that emphasize brief ground contact rather than adding load.

If RSI improves with shorter GCT, consider a small, planned progression (for example, a modest increase in contacts or a slight rise in box height) while maintaining technical consistency. Log decisions and revisit trends weekly so that adjustments are linked to individual responses rather than group averages.

An 8-week plyometric mesocycle performed with concurrent coach-prescribed strength may therefore improve SJ, CMJ, DJ height, and DJ RSI in competitive Taekwondo athletes, particularly when implemented during the general preparation period and monitored with DJ metrics over time.

The study was approved by the Institutional Ethics Committee of the affiliated academic center, and all participants provided written informed consent in accordance with the Declaration of Helsinki.

I am grateful to the athletes who volunteered their time and effort throughout the training and testing period, and to the coaching staff for their professional collaboration in coordinating sessions and adjusting the study and training schedule.