A Systematic Review with Meta-Analysis on the Effects of Plyometric-Jump Training on the Physical Fitness of Combat Sport Athletes

ess the athletic performance changes in combat sport athletes (CoSAs) after plyometric-jump training (PJT), compared to control conditions, through a systematic review with meta-analysis. Following PRISMA guidelines, three electronic databases were searched for includable articles, according to a PICOS approach. Using a random-effects model, Hedges' g effects sizes (ES) were calculated. Heterogeneity was assessed using the I 2 statistic, with values of <25%, 25–75%, and >75% representing low, moderate, and high levels of heterogeneity, respectively. Statistical signi cance was set atp 0.05. The certainty of evidence was assessed

electronic databases were searched for includable articles, according to a PICOS approach. Using a random-effects model, Hedges' g effects sizes (ES) were calculated. Heterogeneity was assessed using the I 2 statistic, with values of <25%, 25–75%, and >75% representing low, moderate, and high levels of heterogeneity, respectively. Statistical signi cance was set atp 0.05. The certainty of evidence was assessed using the GRADE approach. Twelve eligible articles were identi ed for systematic review, seven of high quality and ve of moderate quality, according to the PEDro scale. The studies recruited taekwondo, silat, wrestling, judo, fencing, and karate athletes (292 total participants), including speci c–active and active controls. Most participants had a mean age of <18 years and were males (n= 225). Compared to the control, PJT programmes, involving 4–12 weeks and 2–3 sessions per week, induced small to moderate improvements (ES = 0.47 to 1.04) in athletes' maximal strength (e.g., 1RM squat), vertical jump height, change-of-direction speed, and speci c performance (e.g., fencing movement velocity), although without meaningful effects on body mass, fat mass, and muscle mass (ES = 0.02 to 0.06). Most(7 of 8)outcomes attained low heterogeneity. The outcome-level GRADE analysis indicated a certainty of evidence from low to moderate. In conclusion, PJT, when compared to control conditions, may improve CoSA athletic performance. Keywords: plyometric exercise; human physical conditioning; resistance training; muscle strength; musculoskeletal and neural physiological phenomena; musculoskeletal physiological phenomena; exercise; sports science; sports medicine; athletic performance 1. Introduction Combat (contact) sports typically entail one-on-one combat between competitors under a speci c ruleset [1], involving disciplines that are highly popular worldwide, which is consistent with the increase in the number of published papers on the subject in recent years [2,3]. Combat sports can, typically, be classi ed into percussive sports (i.e., karate, taekwondo, boxing, fencing) or dominance sports (i.e., wrestling, judo) [4]. Among these Sports2023,11, 33.

Sports2023,11, 33 2 of 17 combat sports, many are part of the Olympic games [5,6], such as boxing, wrestling, fencing, judo, taekwondo, and karate. Other combat sports, such as Brazilian jiu-jitsu and mixed martial arts, are popular and expanding [7]. Of note, combat sports are characterized by posing high demands on the athletes' physical tness [8–10]. Indeed, the competitive level of combat sport athletes (CoSAs) might be differentiated according to their athletic performance. For example, standing long jump performance (p= 0.03) and 10 5 shuttle run performance (p< 0.001) were higher in elite vs. sub-elite athletes, and 10 5 shuttle run performance was related to competitive success (R 2 = 0.221;p= 0.006) in female karate athletes [11]. Further, one-repetition maximum (1RM) and muscle power in upper and lower extremities predicted 89.1% achievement of elite level, and Wingate test (crank–arm) peak power predicted male wrestling success (odds ratio = 0.987;p= 0.001) [12]. In addition, body composition can be related to jiu jitsu athletes' performance levels [13–15]. Therefore, it is important that CoSAs implement optimal training activities to de- velop athletic performance components associated with success (e.g., muscle strength and power, agility, and body composition) [16–22]. Several supplemental training meth- ods are routinely used by CoSAs to optimize their athletic performance [16–26]. Among these, plyometric-jump training (PJT) can induce signi cant bene ts [27–34] in muscle strength [35], power [36], and body composition [28,30]. PJT exercises involve the use of rapid eccentric and concentric muscle–tendon actions (i.e., stretch–shortening cycle), with jump exercises involving shorter (e.g., <250 ms) or longer (e.g., 250 ms) ground contact times and maximal jump height/distance (i.e., reactive strength index) as distinctive markers of performance during training sessions [37]. These PJT exercises promote a series of physiological and biomechanical responses (e.g., high rate of force development) that can lead to improved athletic performance [27,37–40]. Indeed, PJT induces neuro-mechanical adaptations [27], with high transference to speci c CoSA performance [41–43]. For exam- ple, experienced male fencers (aged ~25 y) improved their fencing movement times after 12 weeksof PJT combined with resistance training [41]. Similarly, highly trained karate ath- letes (aged

responses (e.g., high rate of force development) that can lead to improved athletic performance [27,37–40]. Indeed, PJT induces neuro-mechanical adaptations [27], with high transference to speci c CoSA performance [41–43]. For exam- ple, experienced male fencers (aged ~25 y) improved their fencing movement times after 12 weeksof PJT combined with resistance training [41]. Similarly, highly trained karate ath- letes (aged ~22 y) applying PJT for 6 weeks, having 2 sessions per week, experienced noted improvements in physical tness, and in markers of injury risk [42]. Moreover, the maximal strength of young (aged ~17 y) male silat athletes improved after 6 weeks of PJT [43]. Further, after 6 weeks of PJT intervention among young (age, 17.8 y) male fencers, PJT induced similar improvements in physical tness (in 13 of 19 measures) when compared to accentuated eccentric training [44]. However, the numbers of CoSAs participating in PJT studies are usually ten or less per group [37,45,46], precluding robust conclusions [47]. Moreover, contrasting ndings have been reported regarding the athletic performances of CoSAs after PJT [10,48]. To address the aforementioned limitations, a systematic review with a meta-analysis approach can offer relevant advancement in the eld [49]. Such an approach also allows the detection of gaps and limitations in the literature, thus providing future research avenues to researchers. Thus, our main aim was to assess the athletic performance changes in CoSAs after PJT, compared to control conditions, through a systematic review (with meta-analysis). We hypothesized that PJT would improve the physical tness and speci c sports abilities of CoSAs compared to controls. 2. Materials and Methods 2.1. Literature Search, Administration, Update, and Inclusion and Exclusion Criteria A systematic review was conducted following international standards (i.e., PRISMA guidelines) [50,51], including speci c recommendations in the eld of PJT [37,46]. Brie y, a systematic scoping review started on April 2017, with updates until November 2022. The search strategy for the databases PubMed, Web of Science, and SCOPUS, and the background of the search history, are described in Table.

eld of PJT [37,46]. Brie y, a systematic scoping review started on April 2017, with updates until November 2022. The search strategy for the databases PubMed, Web of Science, and SCOPUS, and the background of the search history, are described in Table.

Sports2023,11, 33 3 of 17 Table 1.Search strategy (code line) for each database and background of search history. Date of the search April, 2017 May, 2019 August, 2021 Databases PubMed PubMed, WOS (Core Collection), Scopus PubMed, WOS (Core Collection) a , Scopus Keywords “plyometric”, “training” “ballistic”, “complex”, “cycle”, “explosive”, “force”, “plyometric”, “shortening”, “stretch”, “training”, “velocity” “ballistic”, “complex”, “cycle”, “explosive”, “force”, “jump”, “plyometric”, “power”, “shortening”, “stretch”, “training”, “velocity” Database elds for the searchAll PubMed: all WOS: all Scopus: title, abstract, keywords PubMed: all b WOS: all b Scopus: title, abstract, keywords b Restrictions for the search None None None Examples of search strategy code line -PubMed: “plyometric exercise”[MeSH Terms] OR (“plyometric”[All Fields] AND “exercise”[All Fields]) OR “plyometric exercise”[All Fields] OR (“plyometric”[All Fields] AND “training”[All Fields]) OR “plyometric training”[All Fields] -WOS: (ALL = (plyometric)) AND ALL = (training) -SCOPUS: TITLE-ABS-KEY (plyometric AND training) a : except for the keywords “jump” and “power” searched in all WOS databases; b : except for the keywords “jump” and “power” searched in the database eld TITLE (a very poor ef ciency was obtained in the search for results with the incorporation of other database elds); Note: after the formal database search, the list of included articles and the inclusion criteria (see Table) were sent to three independent world experts in the eld of physical tness and sport-speci c performance, plyometric jump training, and combat sport athlete (https://www.expertscape.com/ ex/physical+ tness (accessed on 8 November 2022); help identify additional relevant articles. Additionally, the experts had peer-reviewed publications in the elds of physical tness and sport-speci c performance, plyometric jump training and/or combat sport athlete. The experts were not provided with our search strategy, to avoid biasing their own searches. Upon completion of all these steps, the databases were again consulted in a search for any errata or retractions in any of the included studies. Table 2.Selection criteria used in the systematic review. Category Inclusion Criteria Exclusion Criteria Population Healthy combat sport athletes, with no restrictions on their tness or competitive level, sex, or age. Participants with health problems (e.g., injuries, recent surgery), precluding participation in a plyometric jump

again consulted in a search for any errata or retractions in any of the included studies. Table 2.Selection criteria used in the systematic review. Category Inclusion Criteria Exclusion Criteria Population Healthy combat sport athletes, with no restrictions on their tness or competitive level, sex, or age. Participants with health problems (e.g., injuries, recent surgery), precluding participation in a plyometric jump training program. Intervention A plyometric jump training program, with a minimal duration of 3 weeks, which included unilateral and/or bilateral jumps, which commonly utilize a pre-stretch or countermovement stressing the stretch–shortening cycle. Exercise interventions not involving plyometric jump training (e.g., upper body plyometrics only training interventions) or exercise interventions involving plyometric jump training programs representing less than 50% of the total training load (i.e., volume, e.g., number of exercises) when delivered in conjunction with other training interventions (e.g., high-load resistance training). Comparator Control group (i.e., standard sport training; alternative training intervention; physically active; non-active). Absence of control group. Outcome At least one measure related to physical tness (e.g., countermovement jump height; body fat) and/or sport-speci c performance (e.g., kicking speed) before and after the training intervention. Lack of baseline and/or follow-up data. Study design Multi-arm trials. Single-arm trials/observational studies. One researcher (RRC) oversaw identi cation and screening processes. At the eligibility stage the PICOS approach [50] was considered (Table). Additional exclusion criteria have been previously detailed [37,46]. Brie y, we excluded documents classi ed as books or book chapters, congress abstracts, cross-sectional studies, reviews, and training-related

Sports2023,11, 33 4 of 17 studies without a focus on PJT exercises (e.g., upper body plyometrics). The researchers RRC and PVB individually read and con rmed the eligibility inclusion of full-text studies, with a third author (THV) providing arbitrage, if necessary. Other potentially relevant studies were searched in the lists of references in the included studies. 2.2. Data Extraction Relevant athletic performance attributes for CoSAs [52–62] were considered for data extraction, including 1RM in squat (maximal dynamic strength), vertical squat and coun- termovement jump height, change-of-direction speed (CODS), body mass, fat and muscle mass, and CoSA speci c performance (e.g., fencing movement velocity). These outcomes were considered reliable [63–66], a key element for meta-analysis [50]. If needed, a valid software [67] was used to extract data from studies that presented results only in gure format. 2.3. Studies Methodological Quality A valid and reliable tool (i.e., PEDro scale) [68–70] assessed the studies in eleven dimensions, with ten of these receiving a punctuation for quality assessment, as in previous PJT studies [37,71,72]. Some PEDro scale items (e.g., blinding of participants) [73] are dif cult to accomplish in PJT interventions. Therefore, following previous recommenda- tions [33,71,74] the studies were assessed as with “poor”, “moderate”, or “high” quality if theses achieved 3 points, 4–5 points, or 6–10 points. Two authors (AOA and EB) indepen- dently assessed/con rmed the quality of the studies, with a third author (PVB) providing arbitrage, if necessary. 2.4. Meta-Analyses Although meta-analyses can be performed with 2 studies [75], we considered it more appropriate to perform meta-analyses when at least 3 studies were available for a given outcome [60,76], which was a particularly relevant consideration when taking into account the low number of participants usually involved in PJT studies [37,46,47,77,78]. Using a random-effects model [79,80], the Hedges' g effect sizes (ES) were calculated (Comprehensive Meta-Analysis software; version 3, Biostat, Englewood, NJ, USA) for the included dependent variables, reported with their confidence intervals (95% CIs), and assessed as trivial, small, moderate, large, very large, and extremely large, for values <0.2, 0.2–0.6, >0.6–1.2, >1.2–2.0, >2.0–4.0, >4.0, respectively [81]. If a given study included

a random-effects model [79,80], the Hedges' g effect sizes (ES) were calculated (Comprehensive Meta-Analysis software; version 3, Biostat, Englewood, NJ, USA) for the included dependent variables, reported with their confidence intervals (95% CIs), and assessed as trivial, small, moderate, large, very large, and extremely large, for values <0.2, 0.2–0.6, >0.6–1.2, >1.2–2.0, >2.0–4.0, >4.0, respectively [81]. If a given study included one control group and two or more experimental groups in the meta-analysis, the control group sample size was proportionally divided as per the number of experimental groups [82]. The I 2 statistic was used to assess heterogeneity, with values of <25%, 25–75%, and >75% representing low, moderate, and high heterogeneity, respectively [83]. The extended Egger's test assessed risk of publication bias [84–86] for outcomes with 10 or more studies, and, thereafter, the trim and fill method was used [87], considering a default estimator (L0) for the number of missing studies [88]. Whenp 0.05, the significance was considered for statistical analyses. 2.5. Moderator Analyses The moderator analyses were planned for outcomes with six or more sub-groups to compare (e.g., female vs. male; taekwondo vs. karate; less than eight weeks of PJT compared to more than eight weeks of PJT). When appropriate, the median split technique [89–91] was used for sub-group allocation. 2.6. Certainty of Evidence Two authors (RRC and PVB) assessed/con rmed outcome-level certainty of evidence according to the GRADE recommendations [92–95].

Sports2023,11, 33 5 of 17 3. Results 3.1. Studies Selection, Inclusion, and Quality Assessment Figure were considered eligible for systematic review [10,41,43–45,48,96–100], although two were not included in meta-analyses [98,99]. Most studies (n= 7) attained a high PEDro score ( 6 points), although no study scored >7 points (Table).Sports 2023, 10, x FOR PEER REVIEW 5 of 18 assessed as trivial, small, moderate, large, very large, and extremely large, for values <0.2, 0.2–0.6, >0.6–1.2, >1.2–2.0, >2.0–4.0, >4.0, respectively [81]. If a given study included one control group and two or more experimental groups in the meta-analysis, the control group sample size was proportionally divided as per the number of experimental groups [82]. The I 2 statistic was used to assess heterogeneity, with values of <25%, 25–75%, and >75% representing low, moderate, and high heterogeneity, respectively [83]. The extended Egger’s test assessed risk of publication bias [84–86] for outcomes with 10 or more studies, and, thereafter, the trim and fill method was used [87], considering a default estimator (L0) for the number of missing studies [88]. When p ≤ 0.05, the significance was considered for statistical analyses. 2.5. Moderator Analyses The moderator analyses were planned for outcomes with six or more sub-groups to compare (e.g., female vs. male; taekwondo vs. karate; less than eight weeks of PJT compared to more than eight weeks of PJT). When appropriate, the median split technique [89–91] was used for sub-group allocation. 2.6. Certainty of Evidence Two authors (RRC and PVB) assessed/confirmed outcome-level certainty of evidence according to the GRADE recommendations [92–95]. 3. Results 3.1. Studies selection, inclusion, and quality assessment Figure 1 provides a flow chart illustrating the study selection process. Twelve studies were considered eligible for systematic review [10,41,43–45,48,96–101], although two were not included in meta-analyses [98,100]. Most studies (n = 7) attained a high PEDro score (≥6 points), although no study scored >7 points (Table 3). Figure 1. Search process flow diagram. Figure 1.Search process ow diagram. Table 3.Scores derived from the PEDro rating scale. 1 2 3 4 5 6 7 8 9 10 11 Score a Study Quality Ak n &

in meta-analyses [98,100]. Most studies (n = 7) attained a high PEDro score (≥6 points), although no study scored >7 points (Table 3). Figure 1. Search process flow diagram. Figure 1.Search process ow diagram. Table 3.Scores derived from the PEDro rating scale. 1 2 3 4 5 6 7 8 9 10 11 Score a Study Quality Ak n & Kesilmi¸s, 2020 [45] 1 0 0 0 0 0 0 1 1 1 1 4 Moderate al Syurgawi & Mohamed Shapie, 2019 [43] 1 1 0 1 0 0 0 1 1 0 1 5 Moderate Chaouachi et al., 2014 [96] 1 1 0 1 0 0 0 1 1 1 1 6 High Dallas et al., 2020 [10] 1 1 0 0 0 0 0 1 1 1 1 5 Moderate di Cagno et al., 2020 [44] 1 1 0 1 0 0 0 1 1 1 1 6 High Kontochristopoulos et al., 2021 [48] 1 1 0 1 0 0 0 1 1 1 1 6 High Kosova et al., 2022 [97] 1 1 0 1 0 0 0 1 1 1 1 6 High Lee et al., 2020 [98] 1 1 0 1 0 0 0 1 1 1 1 6 High Ojeda-Aravena, 2020 [9] 1 1 0 1 0 0 0 1 1 1 1 7 High Redondo et al., 2014 [41] 1 1 0 1 0 0 0 1 1 1 1 6 High Sannicandro et al., 2014 [99] 1 1 0 0 0 0 0 0 1 1 1 4 Moderate Singh, 2012 [100] 1 1 0 1 0 0 0 1 1 0 1 5 Moderate A detailed explanation for each PEDro scale item can be accessed at downloads/pedro-scale a From a possible maximal score of 10. 3.2. Study Characteristics The 12 studies included in the systematic review recruited taekwondo, silat, wrestling, judo, fencing, and karate athletes (Table). Most participants ( n= 225, [76.8% of total participants]) were males, and 10 studies recruited youth participants (aged <18 years). Among control groups, two were speci c–active controls [44,98] participating in either accentuated eccentric or

maximal score of 10. 3.2. Study Characteristics The 12 studies included in the systematic review recruited taekwondo, silat, wrestling, judo, fencing, and karate athletes (Table). Most participants ( n= 225, [76.8% of total participants]) were males, and 10 studies recruited youth participants (aged <18 years). Among control groups, two were speci c–active controls [44,98] participating in either accentuated eccentric or balance training, while the remaining controls participated in their standard CoSA routines. The PJT interventions lasted 4–12 weeks, with 2 or 3 weekly sessions (Table).

This review evaluates the impact of plyometric training on combat athletes' physical fitness.