ORIGINAL ARTICLES. PHYSICAL THERAPY Determining the optimal duration of plyometric training for enhancing vertical jump performance: a systematic review and meta-analysis

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Introduction
During the plyometric workout, the muscle is quickly stretched before being quickly contracted.The nervous system is getting ready to react to the cycle of stretching and shortening more swiftly [1].That type of training can improve an athlete's speed, explosive power production, and strengthening of bone [2,3].The main purpose of plyometrics is to improve jumping ability and jumping capability has been assumed by means of essential for effective execution in several sports [4].The importance of jumping ability may vary per sport depending on the direction of the jump.Think about how jumping can be strategically used in team sports like basketball [5], football (soccer) [6,7], and volleyball.Vertical jump height is frequently regarded as an important performance metric [8,9].A training program's plyometric workouts ought to be comparable to the athlete's special requirements concerning the individualities of the athletic activity in which they are participating.To encourage transfer to sport, plyometric workouts should replicate the sort of action known in that discipline, i.e. the specificity principle [10,11].if workouts targeted running performance, such as speed bounding [12,13], the training schedule positively affected running velocity [14][15][16].According to preliminary findings, Plyometric training much improved running and jumping skills as well as enhanced kicking distance [8], balance, and agility [17].
Plyometric training may develop the landing mechanics of the jump [18][19][20].Which increases the strength of the muscle [21].Training instructors and coaches who apply plyometrics in their training should be aware that while this strategy is useful, it does not confirm success in raising vertical jump height [22,23].Equipment, gender, level of participation, diet & food, training time, recovery, economic prospects, and other events that may arise during training can all be variables to consider increasing vertical jump height [2,3,[24][25][26][27][28]. Most authors agree that the frequency and intensity of plyometric exercise should be changed regularly based on the results of intermediate testing [29][30][31][32][33][34][35][36][37].
Previous review studies reported countermovement jump exercises were far better than squat jump exercises in improving vertical jump height.A meta-analytical review conducted by Goran Markovic in Zagreb Croatia revealed 4% higher outcomes of vertical jumps in the group that performed countermovement jump exercises in comparison to squat jump exercises [38].Various factors affecting plyometric training and vertical jump height such as gender, intervention length, type of exercises, and type of sports, considerations were given for outcomes [22].The present study identifies the gap in the previous reviews and attempts to cover the research gap.Observing the quantity and calibers of the available research literature was the aim of this systematic review., to evaluate the efficacy and effectiveness of plyometric training for improving vertical jump height in male and female players [39], and to ascertain whether this method of training could be used to enhance the motor skills of various sports.

Search strategy
A wide-ranging database search on the internet was accomplished via PubMed, MEDLINE, and Google Scholar, to recognize appropriate articles that examined male and female athletes' vertical jump heights after plyometric training using the squat jump and countermovement jump.The following combination of keywords was used by us: plyometric OR cycle of stretching and shortening OR squat jump OR countermovement jumps OR controlled experiments and jumping exercises.The following key phrases were combined to do a manual search: plyometric training, vertical jump, Squat jumps and counter jumps performance of men, and women athletes.Each article's reference lists were also checked to find supplementary appropriate investigations.The archival finding was confined to a journal with peer review journal papers released in English from 1996 through 2022.The Recommended Reporting Items for systematic examinations and Meta-Assessments (PRISMA) guideline was followed in accompanying this systematic review and meta-analysis.[40].

Eligibility criteria
The randomized controlled trials issued during the previous twenty-eight years in English had been taken into contemplation in this systematic review.The consisted of applicants were soccer, basketball, handball, volleyball, badminton, football, gymnasts, and collegiate male and female athletes of any age group (no binding).A minimum of four weeks of plyometric exercise and the presence of a Health, sport, rehabilitation Health, sport, rehabilitation Здоров'я, спорт, реабілітація Здоров'я, спорт, реабілітація Здоровье, спорт, реабилитация Здоровье, спорт, реабилитация (5) Studies that were uncontrolled, cross-sectional, and ( 6) where the results did not distinguish between males and females did not produce distinct outcomes.

Data Extraction
Two reviewers each separately gathered the information on subjects containing (age, gender, sample size,) enlightenment a description of the intervention (exercise kind, extent, length, and frequency range, session) study design and study outcomes, and method (randomization and distribution concealment) One author worked on this (R.PH), Despite the fact that S. LE, an additional author, reviewed the extracted data for accuracy and completeness.One author (J-PB) evaluated the content's quality.A third reviewer or agreement was used to resolve disagreements.Reviewers did not know the writers, organizations, or script journals.

Risk of Bias Assessment
Using the Cochrane technique separately, the risk of bias was evaluated by two authors (R. PH & S. LE) [41,42].This tool assesses the risk of bias by evaluating each of the seven criteria: sequential generation, allocated, deception, participant and staff illuminating, concealment of outcome assessment, inadequate outcome data, selective reporting, and additional sources of bias.The risk of bias was graded as (1) low, (2) unclear, or (3) high on each of the criteria.The consensus was reached through conversation after discrepancies were doublechecked with a third reviewer (J.PB).

Data synthesis
The degree of training effects was assessed using effect size calculation as per the equations given below.Cohen's d is one of the most commonly used effect size measures.It is particularly useful when comparing the means of two groups or conditions.Cohen's d is calculated by taking dividing the variation between the two groups' mean differences by the combined standard deviation (see Equation 1, and 1.1).A minimum of two studies having similar assessment outcomes were used for subgroup analysis.A random effect method was used to determine the pooled effect of countermovement jump and squat jump training on vertical jump height performance.The degree of the size of the calculated effects ranged as follows: small (0.2), medium (0.5), and large (0.8) [43].The current version, the review manager 5.4 tool was used for the above-cited method of data synthesis [44,45].Equation 1Where, D = raw mean difference, n 1, and n 2 are the sample size in group one and group two, S 1 and S 2 are the standard deviation in group one and group two.

Equation 1.1
Heterogeneity also called inconsistency in systematic reviews refers to the variability or diversity among the results of separate studies that are included in the analysis.Statistical strategies include a meta-analysis used to combine the findings from numerous independent studies on a particular research question to obtain an overall estimate of the effect size or association.Heterogeneity is an important consideration in meta-analysis because it can impact the construal and generalizability of the results.To assess the degree of heterogeneity, researchers commonly use statistical tests such as Cochran's Q test or the I 2 statistic (see equation 1.2).The Cochran's Q test determines whether the apparent variations between research are merely the result of chance, while the I 2 statistic quantifies the amount of total variability that is due to heterogeneity rather than chance (see equation 1. 122 is defined as I 2 of 0% to 24%, moderate heterogeneity is defined as I 2 of 25% to 49%, substantial heterogeneity is defined as I 2 of 50% to 74%, and considerable heterogeneity is defined as I 2 of 75% to 100% [44,46].The I 2 test was used to determine how much of the observed variation reflected a meaningful difference in effect size and how much of the changes in findings might have been explained by chance alone [46].It was suggested that this ratio be represented by the statistics I 2 , which might act as a proxy for the signal-to-noise ratio.It is calculated as: Where " " is stands for study weight," " is denote the study effects size, "M" is the summary effect and, "k" is the total number of studies.
When a meta-analysis only has a few trials or studies with a small number of participants, this test's accuracy is reduced because of its low power, P ≤ .10 was regarded to designate significant heterogeneity [44].

Study Selection
Overall, 366 articles were classified from the database search during the research years 1996 to 2022.124 studies were left after replacement were detached and articles with poor topics and summaries were eliminated.After the screening by two independent reviewers 50 full-text manuscripts were evaluated for eligibility criteria.22 papers were eventually chosen for the last round of screening and included in the quantitative synthesis (meta-analysis) (Fig. 1).

Study Characteristics
Between 1996 and 2022, all research papers that fulfilled the requirements for enclosure were printed in English.Table No. 2 provides a thorough explanation of studies incorporated in the analysis.The 22 studies' overall total number of subjects was 1023 individuals, and each study's average sample size ranged from 5 to 33 subjects per group.The involvement of interventions in included studies was as follows; one study gives 5 weeks of training [48], four studies give 6 weeks of training [49][50][51][52], one study give 7 weeks of training [53], seven studies give 8 weeks training [54-60], two studies give 10 weeks training [36,37], 3 studies give 12 weeks training [33,34].In these studies, 4 interventions included female subjects and 14 interventions included male participants.To investigate the influence of countermovement, jump training, and squat jump training on vertical jump height thirteen studies had 5 to 8 weeks of training length and five studies had 10 to 12 weeks of training length.In sixteen studies data will be measured in centimeters and two studies data will be measured in meters.two to three alternating training sessions per week was the most preferred training frequency; one study has given 6 to 8 sessions per week [53].Plyometric training sessions lasted between 20 to 120 minutes.One study, however, employed a plyometric exercise programme that required 30 jumps each week (10 jumps on alternate 3 days) for 6 months.[49].

Summary of Squat Jump
The squat jump training group's overall effect on the vertical jump is favorable.Sixteen effects (73%) were greater than zero.The mean effect size Cohen's d for overall effects size was 0.96 [95% CI, 0.57 -1.35; Z = 4.88, (P < 0.00001)].More specifically, the squat jump training is associated with higher vertical jump compared to the control group.
A moderate but significant amount of heterogeneity [ Tau = 0.56; chi-square = 79.97,df = 19 (P < 0.0001) I 2 = 76%] and risk of bias were observed in overall study effects to detect the inexplicable variances between study estimates, method of subgroup analysis was approached to explain the heterogeneity.
The pooled effects of the first subgroup i.e., males and females separately reported in the table no 3.The overall effects in male subgroups favor the squat jump training group the mean effect size was There are no subgroup effects by gender of the participants.The test for subgroup difference does not indicate a significant difference in training effects between the subgroups of male and female participants (

Summary of countermovement jump
The countermovement jump has a positive overall effect on the countermovement jump training group.Seventeen effects (77%) were greater than zero.The mean effect size of Cohen's d for overall effects size was 0.91[95% CI 0.46 -1.37; Z = 3.93, (P < 0.0001)].Countermovement jump training, in particular, is related to a greater vertical jump in comparison to the control group.
A moderate but significant amount of heterogeneity [ Tau = 0.90; chi-square = 117.91,df = 20 (P < 0.00001) I 2 = 83%] and risk of bias were observed in overall Study effects to detect the unexplained differences between study estimates, method of subgroup analysis was approached to explain the heterogeneity.
The pooled effects of the first subgroup i.e., males and females separately reported in the forest plot (fig - 4).The overall effects in male subgroups favor the countermovement jump training group the mean effect size was 1.12 [95% CI 0.

Discussion
This study evaluates the effects of squat jump and countermovement jump training programs on vertical jump height performance of the different types of disciplines.The findings of this systematic review and meta-analysis validated the value of plyometric exercise for athletes.The plyometric training effects on the squat jump and countermovement jump performance ranged from minor to very large.Studies included different cultures and across the globe such as the USA, Italy, Alabama, Turkey, Canada, Norway, Switzerland, Belgium, Serbia, Tunisia, Japan, Greece, Spain, Poland.subjects belong to different disciplines i.e., basketball, volleyball, handball, track events, soccer, football, badminton, gymnasts, untrained, health volunteered, college students, and physical education students have included the present metaanalysis.
Our meta-analytical results are consistent with earlier research that investigated the effects of plyometric training on vertical jump height in male and female volunteers from various fields [17,36,49,53].When we looked at research done in the past to examine the effects of plyometric exercise, we found that it improves vertical jump height [2,29,32,62] The meta-analyses that were carried out in this review applied non-plyometric training groups (control) that did not distinguish between physically active and inactive participants (e.g., only pre and post-data were taken from the control group), as well as between subjects in the control group who were physically engaged daily.Different sorts of equipment and environments were used in the plyometric approaches that were examined.While the study [68] revealed that the benefits of plyometric training in jumping performance are stronger for interventions of 10 weeks or more, 14 of the 17 investigations lasted less than 10 weeks.Additionally, variations in plyometric leaps, total jumps, and workout intensity are seen among studies.
The studies including vertical jump height concerning squat jump and countermovement jump exercises were taken from previous studies to review the effect of plyometrics training on vertical jump height.Two subgroups were created in SJ (1-squat jump gender group & 2-intervention length group and in addition, two subgroups in countermovement jump (1-counter movement jump gender group & 2-intervention length group) for primary outcome analysis and closer scrutiny Subgroup squat jump males after the data analysis show that there was a significant effect of squat jump training on male athletes for increasing vertical jump height fig- 1.
Along with this, a study in the subgroup squat jump male also shows that squat jumps have no significant effect [48] In this study, handball male players were given 5 weeks of plyometric training, after the results of which it was found that the training period was too short that's why there was no significant effect observed).Along with this, we get to see significant effects in the study group female, which suggests that squat jump can increase vertical jump height in women.

Limitations
The outcomes of this analysis should be explained with some limitations.The insufficient findings made it difficult to reach specific conclusions.Some consist of studies involving somewhat small intervention groups.Most of the studies did not describe the intensity of the training Health, sport, rehabilitation Health, sport, rehabilitation Здоров'я, спорт, реабілітація Здоров'я, спорт, реабілітація Здоровье, спорт, реабилитация Здоровье, спорт, реабилитация 2023 9(3) 129 intervention.Therefore, the possible relationship between intensity and the related factor of plyometric training is still unclear.In addition, just four research featured young athletes, making it insufficient to employ chronological age as a moderator variable in the study.Another drawback was that the majority of the papers included in this study had low ('poor') quality of methodology ratings.It is challenging to come to any firm findings due to the few studies that have been conducted.The number of subjects in included interventions was also not sufficient (min-05, max-30).The smaller number of participants decreases the validity of obtained outcomes.It is advised that more study enhances the caliber of their study designs by inspecting the impact of plyometric training on jump efficiency.

Conclusion
The present study shows that countermovement jumps and squat jump in plyometric training improve the vertical jump height of male and female athletes.while a high degree of effect was observed in the studies containing male subjects.Large effects observed in prerequisites for the synthesis of data to encompass the study.The control groups either did not exercise or participated in any regular sports activity without plyometric training.The involved articles have to specify the vertical jump height as the result metric for at least one of the squat jump and countermovement jump movement patterns.Follows exclusion were implemented: (1) studies did not use proper training plans for respondents; (2) those academic papers that weren't authored in English; (3) studies did not show the control group; (4) studies with a combined of plyometric, weight training and resistance training in directive to minimize the consequences of combination training; 3).Higher values of I 2 indicate greater heterogeneity.The I 2 statistics were used to analyze the degree of heterogeneity, which was then categorized as follows: Low heterogeneity Health, sport, rehabilitation Health, sport, rehabilitation Здоров'я, спорт, реабілітація Здоров'я, спорт, реабілітація Здоровье, спорт, реабилитация Здоровье, спорт, реабилитация 2023 9(3) 1.06 [95% CI, 0.57 -1.55; Z = 4.27 (P < 0.0001)].While the overall effects in the female sub-group also favor the squat jump training.The mean effect size was 0.59 [95% CI, 0.24 -0.95; Z = 3.28 (P < 0.001)].Similarly, the pooled effects of the second subgroup i.e., intervention length group 5 to 8 weeks and 10 to 12 weeks separately reported in the forest plot (fig -3) the overall effects in intervention length of 5 to 8 weeks subgroups favor the squat jump training group.The mean effect size was 0.79 [ 95 % CI, 0.38 -1.20: Z = 3.75 (P < 0.0002)].While the overall effects in the intervention length 10 to 12 weeks subgroups give preference to the squat jump training group.The mean effect size was 1.65 [ 95 % CI 0.63 -2.67; Z = 3.17 ( P < 0.002)].
59 -1.66; Z = 4.09 (P < 0.0001)].While the overall effects in the female sub-group also favor the countermovement jump training.The mean effect size was 0.14 [95% CI 0.49 -0.76; Z = 0.43 (P < 0.67)].Similarly, the pooled effects of the second subgroup i.e., intervention length group 5 to 8 weeks and 10 to 12 weeks separately reported in the forest plot (fig -5) the overall effects in intervention length of 5 to 8 weeks subgroups favor the countermovement jump training group.The mean effect size was 0.79 [95 % CI 0.30 -1.29: Z = 3.15(P < 0.002)].While the overall effects in the intervention length of 10 to 12 weeks subgroups give preference to the countermovement jump training group.The mean effect size was 1.35 [95 % CI 0.11 -2.58; Z = 2.14 (P < 0.03)].

Fig. 1 .
Fig. 1.The study selection is depicted in a flowchart.(retrieved from:[47]) . The effects of various jump patterns' vertical jump performance on plyometric training vary.Jumps with countermovement, squats, and drops were all anticipated.[2,18,63,64].It has been proposed that plyometric training is greater success in enhancing performance in jumps that use the brief stretch cycle of muscle because it improves the elastic properties of the muscle-tendon unit as well as the neuronal the involved motor units' firing patterns and order [4,63,65-67].The duration of training interventions consisted of studies extended from 5 to 12 weeks and 2 to 6 days of training were given in one week, in which 2 to 15 sessions were given in a one-week training.A total of 1143 subjects (experimental group n-582 and control group n-561) have participated in 22 RCTs (randomized controlled trials).Most of the studies were based on moderate to high int ensity[37,49,51,55,58,60,61].high intensity-based training was most helpful for increasing the vertical jump height . 2 to 6 days of training were given in one week, in which 2 to 15 sessions were given for a week of training 20 to 120 min.The plyometric training effect may also be influenced by an athlete's background and current training status.Compared to untrained and professional athletes, amateurs and trainee athletes will likely respond more quickly and have an increase in jump performance.
countermovement jump in comparison to squat jump training.The effectiveness of plyometric training also seems to depend on the length of the interventions.Greater improvements in vertical jump performance are produced by longer training weeks.Finally, plyometric exercise can be used as a beneficial training method to improve athletes' vertical jump height performance in many different kinds of sports.Short-term effects of strength and plyometric training on sprint and jump performance in professional soccer players.The Journal of Strength & Conditioning Research.2008;22(3):773-80.54.Toumi H, Best TM, Martin A, F'guyer S, Poumarat G. Effects of eccentric phase velocity of plyometric training on the vertical jump.Int J Sports Med.2004;25(05):391-8.55.Holcomb WR, Lander JE, Rutland RM, Wilson GD.The effectiveness of a modified plyometric program on power and the vertical jump.The Journal of Strength & Conditioning Research.1996;10(2):89-92.56.Chelly MS, Hermassi S, Aouadi R, Shephard RJ.Effects of 8-week in-season plyometric training on upper and lower limb performance of elite adolescent handball players.The Journal of Strength & Conditioning Research.2014;28(5):1401-10.57.Meylan C, Malatesta D. Effects of in-season plyometric training within soccer practice on explosive actions of young players.The Journal of Strength & Conditioning Research.2009;23(9):2605-13.58.Hammami M, Gaamouri N, Ramirez-Campillo R, Shephard RJ, Bragazzi NL, Chelly MS, et al.Effects of high-intensity interval training and plyometric exercise on the physical fitness of junior male handball players.Eur Rev Med Pharmacol Sci.2021;25(23):7380-9.59.Bogdanis GC, Donti O, Papia A, Donti A, Apostolidis N, Sands WA.Effect of plyometric training on jumping, sprinting and change of direction speed in child female athletes.Sports.2019;7(5):116.60.Padrón-Cabo A, Lorenzo-Martínez M, Pérez-Ferreirós A, Costa PB, Rey E. Effects of plyometric training with agility ladder on physical fitness in youth soccer players.Int J Sports Med.2021;42(10):896-904. 61.Ronnestad BR, Kvamme NH, Sunde A, Raastad T. Short-term effects of strength and plyometric training on sprint and jump performance in professional soccer players.The Journal of Strength & Conditioning Research.2008;22(3):773-80.62. Rubley MD, Haase AC, Holcomb WR, Girouard TJ, Tandy RD.The effect of plyometric training on power and kicking distance in female adolescent soccer players.The Journal of Strength & Conditioning Research.2011;25(1):129-34.63.Markovic G, Mikulic P. Neuro-musculoskeletal and performance adaptations to lowerextremity plyometric training.Sports medicine.2010;40(10):859-95.64.Carvalho A, Mourão P, Abade E. Effects of strength training combined with specific plyometric exercises on body composition, vertical jump height and lower limb strength development in elite male handball players: a case study.J Hum Kinet.2014;41:125.65.Weiss LW, Relyea GE, Ashley CD, Propst RC.Using velocity-spectrum squats and body composition to

Table 1
Studies Characteristics

Table 3
Shows summary of effects of squat jump training about male and female subgroups analysis

Table 4
Shows the summary of the effects of squat jump training on the intervention length of male and female subgroups

Table 5
Shows a summary of the effects of countermovement jump in male and female subgroups

Table 6
Shows a summary of the effects of countermovement jump about intervention length of male and female subgroups