The Effect of Two Plyometric Training Techniques on Muscular Power and Agility in Youth Soccer Players

RESEARCH NOTE

THE EFFECT OF TWO PLYOMETRIC TRAINING TECHNIQUES ON MUSCULAR POWER AND AGILITY IN YOUTH SOCCER PLAYERS

1 2 1 KEVIN THOMAS, DUNCAN FRENCH, AND PHILIP R. HAYES 1Division of Sport Sciences, Northumbria University, Newcastle-upon-Tyne, United Kingdom; and 2English Institute of Sport, Gateshead, United Kingdom

ABSTRACT (8,14,30,31) and decreases in sprint and acceleration times (10,18,26,30). Thomas, K, French, D, and Hayes, PR. The effect of two plyometric Some research in plyometrics has investigated the effect of training techniques on muscular power and agility in youth soccer exercise mode on performance. Countermovement jump players. J Strength Cond Res 23(1): 332–335, 2009—The aim of (CMJ) and depth jump (DJ) training have both improved this study was to compare the effects of two plyometric training vertical jump height, with no significant difference between techniques on power and agility in youth soccer players. Twelve the two modalities (8,14,17). Bobbert (4) has speculated males from a semiprofessional football club’s academy (age = that using CMJ or DJ techniques may result in differences 17.3 6 0.4 years, stature = 177.9 6 5.1 cm, mass = 68.7 6 5.6 in training adaptations, arguing that a DJ would trigger kg) were randomly assigned to 6 weeks of depth jump (DJ) or improvement in the power output capacity of muscles, countermovement jump (CMJ) training twice weekly. Participants whereas repetition of the CMJ would improve coordination. in the DJ group performed drop jumps with instructions to Young et al. (34) attempted to investigate these assumptions, minimize ground-contact time while maximizing height. Partic- but their study was hampered by an inadequate training ipants in the CMJ group performed jumps from a standing start volume and intensity. The potential improvements from plyometrics as measured position with instructions to gain maximum jump height. by vertical jump and sprint performance would be beneficial Posttraining, both groups experienced improvements in vertical to soccer (2,23). The basic movement patterns in soccer also jump height (p , 0.05) and agility time (p , 0.05) and no change require high levels of agility (11,24). Agility requires rapid in sprint performance (p . 0.05). There were no differences force development and high power output, as well as the between the treatment groups (p . 0.05). The study concludes ability to efficiently utilize the stretch shortening cycle in that both DJ and CMJ plyometrics are worthwhile training activities ballistic movements (21). Plyometric training has been for improving power and agility in youth soccer players. shown to improve these requirements (1,5,15), and Besier et al. (3) have recommended the inclusion of plyometrics in KEY WORDS plyometrics, depth jump, countermovement, soccer training to familiarize players with unanticipated stretch-shortening cycle changes in direction. The aim of the present study was to compare the effectiveness of CMJ and DJ plyometric training modalities on muscular power and agility in soccer players. INTRODUCTION

lyometric training—jumping, bounding, and hop- METHODS ping exercises that use the stretch shortening cycle Experimental Approach to the Problem of the muscle unit—have consistently been shown Using a randomized, between-group design, 12 soccer players to improve the production of muscle force and P were assessed for leg power, sprint speed, and agility pre and power (15,30). In particular, the fast force production of post 6 weeks of DJ or CMJ training. the trained muscle improves, coupled with smaller increases in maximum isometric force (15). These physiological Participants adaptations have facilitated increases in vertical jump height After institutional ethics approval, 15 males from a semiprofessional soccer academy gave written informed consent Address correspondence to Kevin Thomas, kevin2.thomas@northumbria. to take part in the study after completion of a screening ac.uk. questionnaire. Parental consent was obtained for participants 23(1)/332–335 under 18 years of age. The study was conducted in season, Journal of Strength and Conditioning Research where participants attended soccer training two to four times Ó 2009 National Strength and Conditioning Association per week and played competitive matches at least once 332 Journalthe of Strength and Conditioning ResearchTM

a week. All participants had been involved in soccer training of this regularity for . 4 years before the study. Participants were randomly assigned to DJ and CMJ jump groups. Twelve TABLE 1. Limits of agreement (LOA) and intraclass participants (age = 17.3 6 0.4 years, height = 177.9 6 5.1 cm, correlations (ICC) for outcome measures. weight = 68.7 6 5.6 kg) successfully completed the study. LOA ICC Procedures 5 m (s) 0.01 6 0.12 0.93 Training. Plyometric training was undertaken twice a week 10 m (s) 0.01 6 0.13 0.96 for 6 weeks. Participants in the CMJ group performed exer- 15 m (s) 0.01 6 0.18 0.94 cises that always began with a countermovement, defined as 20 m (s) 0.01 6 0.15 0.98 a flexion of the knees. During rebound exercises, participants Agility 505 (s) 0.01 6 0.05 0.99 CMJ (cm) 1 6 2 0.94 in this group were told to ‘‘damp’’ their landings each time and to gain maximum height through knee flexion. Participants in CMJ = countermovement jump. the DJ group performed exercises that always began with a drop from a height (40 cm). Participants in the DJ group were instructed to minimize ground-contact time while maximizing height. These instructions were emphasized completed three trials each—one practice and two recorded during every session through the use of demonstrations, with at least 4 minutes of recovery between each trial. verbal cues, and exercise sheets. Statistical Analyses The intensity of each program was subjectively equated Descriptive statistics are represented as mean (SD). The mean of using Chu’s (7) and Potach and Chu’s (22) classification of the recorded jumps was used as the score for CMJ height. The plyometric exercise intensities. The type of exercise that each best times for 5, 10, 15, and 20 m were used as the final results group performed was matched by intensity and, where (11). The fastest agility score was used in the analyses. Tests of possible, by similar jumps. The height of the DJ box remained normal distribution (Kolmogorov-Smirnov and Levene’s) were at 40 cm to ensure that intensity increased as a function of conducted on all data before analysis. All data were normally exercise and not as a function of increased eccentric load, distributed (p . 0.05). A mixed-factorial ANOVA with repeated which could not be manipulated in the CMJ condition. measures on one factor assessed main effects for time, group, Sessions began at 80 foot contacts and progressed to 120 by and the time 3 group interaction. Effect size was calculated by the end of training (22). The program was incorporated into training group for each outcome measure (difference between their usual twice-weekly training regime. Participants also means/pooled SD). Post hoc statistical power calculations were continued their usual competitive program of matches. performed using GPower software (12). Statistical significance Participants were asked to refrain from any other form of was set at p # 0.05. Data analysis was performed using SPSS training that could affect the variables measured. (version 11.5, SPSS Inc., Chicago, Ill). Testing. Participants were tested pre and post the 6-week training period. Before testing, participants performed a 5-min- RESULTS ute warm-up protocol consisting of submaximal running, active After 6 weeks of training, there were increases in vertical jump stretching, and jumping exercises. This warm-up was chosen height (F ½1, 10 = 42.22, p , 0.05, Figure 1) and decreases in because of its positive effects on power production (32). Table 1 agility times (F ½1, 10 = 60.97, p , 0.05, Figure 2) for both shows the test-retest limits of agreement and intraclass correlations for each dependent variable. Countermovement vertical jump height (cm) was measured using a vertical jump mat and belt (Takei Jump Meter, Japan). Participants were instructed to keep their hands on their hips at all times and were permitted two trials (. 15 seconds of recovery) to practice jumping technique followed by two recorded jumps. Light gates were used to measure sprint speed and agility (NewTest, Kiviharjuntie, Finland). Sprint speed from a standing start was assessed for 20 m with 5-m splits. Each participant completed three trials—one practice and two recorded with at least 4 minutes of recovery between each trial. The 505 agility test was employed to assess agility. The 505 agility test is designed to minimize the

inﬂuence of individual differences in running velocities while Figure 1. Vertical jump height (cm) separated by group pre- and accentuating the effect of acceleration immediately before, posttraining. during, and after the change of direction (11). Participants

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Time to complete the 505 agility test decreased for both groups. In contrast to straight sprinting, agility involves greater emphasis on deceleration and subsequent reactive coupling with acceleration (21). Leg muscle power has been moderately correlated with agility (19,20), as has reactive strength (33). Leg muscle power, as measured by the vertical jump, improved for both treatment groups. Neuromuscular adaptations related to firing frequencies and patterns are also likely to have occurred (15). These speculated adaptations could have improved the ability to rapidly and forcefully switch from decelerating to acceler- ating movements. The magnitude of increases in strength and power after Figure 2. Agility time (seconds) separated by group pre- and training has been shown to be dependent on how similar the posttraining. test is to the actual training exercise (28), reflecting the role of learning and coordination (27). Although the participants were experienced soccer players, their previous training did groups. There were no changes in sprint speed (F ½1, 10 = not include any type of jump training or specific maximal- 0.14, p . 0.05, Table 2) and no differences between the intensity change-of-direction exercises similar to those treatment groups at improving the variables measured. employed in the study. Thus, it is likely that a meaningful For vertical jump height, DJ training resulted in a meaning- learning effect was present. Future studies should fully ful effect size of 1.1. Countermovement jump training resulted habituate participants to the testing procedures to control for in a moderate-high effect size of 0.7. For agility, DJ and CMJ this effect. training resulted in meaningful effect sizes of 1.3 and 1.5, There were no differences in acceleration or sprint speed respectively. The post hoc statistical power for these analyses posttraining. These findings support studies showing no was low to moderate (23–73%). improvements in sprint speed after a plyometric program (13,31). Repeated ballistic exercise could potentially improve the ability to generate explosive ground-reaction DISCUSSION forces (9,16). Ground-contact times in plyometric bounce The results of this study show that DJ and CMJ plyometric DJ and CMJ activities have been reported from 300 training can positively affect vertical jump and agility milliseconds (6) to , 200 milliseconds, and . 400 performance in soccer players, with no significant difference milliseconds (34), respectively. In sprinting, ground-contact between modes. times decrease from , 200 milliseconds at acceleration to , Vertical jump height increased for both training groups. 100 milliseconds at top speed (21). In terms of the velocity The improvement in jump height indicates that adaptations specificity principle of training, it is likely that the ground- relating to increases in leg power have occurred. The contact times were not short enough to elicit an increased adaptations to both forms of training are likely to be neural ability to generate explosive ground-reaction forces during because these predominate in the early stages of strength and sprinting. power training (29) and have been shown to be the main There were no differences between the DJ and CMJ groups. adaptation to plyometric exercise (15). There were differences in effect sizes between groups, suggesting that the two modes of training could have different magnitudes of effect on the performance variables mea- TABLE 2. Sprint time (seconds) separated by group pre- and posttraining. sured. The small sample size, DJ (n = 7) CMJ (n =5) low statistical power, and short training period restrict any con- Pretest Posttest Pretest Posttest clusions; however, this area 5 m (s) 1.03 6 0.06 1.05 6 0.10 1.06 6 0.07 1.07 6 0.14 warrants further research. 10 m (s) 1.76 6 0.06 1.78 6 0.16 1.81 6 0.09 1.81 6 0.18 15 m (s) 2.45 6 0.07 2.44 6 0.17 2.52 6 0.11 2.50 6 0.23 PRACTICAL APPLICATIONS 20 m (s) 3.10 6 0.11 3.07 6 0.22 3.18 6 0.14 3.16 6 0.27 There were no differences be- DJ = depth jump; CMJ = countermovement jump. tween treatment groups, indi- cating that both forms of training were effective. Depth 334 Journalthe of Strength and Conditioning ResearchTM

jump training is commonly thought to be a more effective 16. Harland, MJ and Steele, JR. Biomechanics of the sprint start. Sports training mode than CMJ (4,34), but no study has yet to show Med 23: 11–20, 1997. greater significant improvements in leg power compared 17. Holcomb, WR, Lander, JE, Rutland, RM, and Wilson, GD. The effectiveness of a modified plyometric program on power and the with CMJ training (8,14,17). The results of this study vertical jump. J Strength Cond Res 10: 88–92, 1996. highlight the potential of using both plyometric training 18. Kraemer, WJ, Ratamess, NA, Volek, JS, Mazzetti, SA, and Gomez, techniques to improve the power-related components of AL. The effect of the meridian shoe on vertical jump and sprint soccer thought to be necessary for success (25). performances following short-term combined plyometric/sprint and resistance training. J Strength Cond Res 14: 228–238, 2000. REFERENCES 19. Mayhew, JL, Piper, FC, Schewgler, TM, and Ball, TE. Contributions 1. Anderson, FC and Pandy, MG. Storage and utilization of elastic of speed, agility and body composition to anaerobic power measurements in college football players. 3: strain energy during jumping. J Biomech 26: 1413–1427, 1993. J Appl Sport Sci Res 101–106, 1989. 2. Bangsbo, J. The physiology of soccer—with special reference 20. Negrete, R and Brophy, J. The relationship between isokinetic open to intense intermittent exercise. Acta Physiol Scand Suppl 619: 1–155, 1994. and closed chain lower extremity strength and functional performance. J Sport Rehabil 9: 46–61, 2000. 3. Besier, TF, Lloyd, DG, Ackland, TR, and Cochrane, JL. Anticipatory effects on knee joint loading during running and cutting maneuvers. 21. Plisk, SS. Speed, agility and speed endurance development. In: (2nd ed.). Baechle T.R. Med Sci Sports Exerc 33: 1176–1181, 2001. Essentials of Strength Training and Conditioning and Earle, R.W. eds. Human Kinetics, 2000. pp. 427–470. 4. Bobbert, MF. Drop jumping as a training method for jumping ability. 22. Potach, DH and Chu, DA. Plyometric training. In: Sports Med 9: 7–22, 1990. Essentials of Strength Training and Conditioning (2nd ed.). Baechle T.R. and Earle, 5. Bobbert, MF, Gerritsen, KG, Litjens, MC, and Van Soest, AJ. Why is R.W. eds. Human Kinetics, 2000. pp. 427–470. countermovement jump height greater than squat jump height? Med 23. Reilly, T, Bangsbo, J, and Franks, A. Anthropometric and Sci Sports Exerc 28: 1402–1412, 1996. physiological predispositions for elite soccer. J Sports Sci 18: 6. Bobbert, MF, Huijing, PA, and Van Ingen Schenau, GJ. Drop 669–683, 2000. jumping. I. The influence of jumping technique on the biomechanics 24. Reilly, Tand Doran, D. Fitness assessment. In: (2nd of jumping. Med Sci Sports Exerc 19: 332–338, 1987. Science and Soccer ed.). Reilly T. and Williams, M.A. eds. Routledge, 2003. pp. 21–46. 7. Chu, D. Jumping Into Plyometrics. Champaign: Human Kinetics, 1992. 25. Reilly, T, Williams, AM, Nevill, A, and Franks, A. A multidisciplinary 8. Clutch, D, Wilton, M, McGown, C, and Bryce, GR. The effect of approach to talent identification in soccer. J Sports Sci 18: 695–702, depth jumps and weight training on leg strength and vertical jump. 2000. Res Q 54: 5–10, 1983. 26. Rimmer, E and Sleivert, G. Effects of a plyometrics intervention 9. Delecluse, C. Influence of strength training on sprint running program on sprint performance. J Strength Cond Res 14: 295–301, performance. Current findings and implications for training. Sports 2000. Med 24: 147–156, 1997. 27. Rutherford, OM and Jones, DA. The role of learning and 10. Delecluse, C, Van Coppenolle, H, Willems, E, Van Leemputte, M, coordination in strength training. Eur J Appl Physiol Occup Physiol 55: Diels, R, and Goris, M. Influence of high-resistance and high-velocity 100–105, 1986. training on sprint performance. Med Sci Sports Exerc 27: 1203–1209, 1995. 28. Sale, D and MacDougall, D. Specificity in strength training: a review for the coach and athlete. Can J Appl Sport Sci 6: 87–92, 1981. 11. Ellis, L, Gastin, P, Lawrence, S, Savage, B, Buckeridge, A, Stapff, A, Tumilty, D, Quinn, A, Woolford, S, and Young, W. Protocols for the 29. Sale, DG. Neural adaptation to resistance training. Med Sci Sports 20: S135–S145, 1988. physiological assessment of team sports players. In: Physiological Tests Exerc for Elite Athletes. C.J. Gore, ed. Champaign: Human Kinetics, 2000. 30. Wagner, DR and Kocak, MS. A multivariate approach to assessing pp. 128–144. anaerobic power following a plyometric training program. J Strength 11: 251–255, 1997. 12. Faul, F and Erdfelder, E. Gpower: A Priori, Post-Hoc and Compromise Cond Res Power Analyses for MS-DOS [Software]. Bonn: Bonn University, 1992. 31. Wilson, GJ, Newton, RU, Murphy, AJ, and Humphries, BJ. The 13. Fry, AC, Kraemer, WJ, Weseman, CA, Conroy, PB, Gordon, SE, optimal training load for the development of dynamic athletic Hoffman, JR, and Maresh, CM. The effects of an off-season strength performance. Med Sci Sports Exerc 25: 1279–1286, 1993. and conditioning program on starters and non-starters in women’s 32. Young, WB and Behm, DG. Effects of running, static stretching and intercollegiate volleyball. J Appl Sport Sci Res 5: 174–181, 1991. practice jumps on explosive force production and jumping 14. Gehri, DJ, Ricard, MD, Kleiner, DM, and Kirkandall, TD. A performance. J Sports Med Phys Fitness 43: 21–27, 2003. comparison of plyometric training techiques for improving 33. Young, WB, James, R, and Montgomery, I. Is muscle power related vertical jump ability and energy production. J Strength Cond Res to running speed with changes of direction? J Sports Med Phys Fitness 12: 85–89, 1998. 42: 282–288, 2002. 15. Hakkinen, K, Alen, M, and Komi, PV. Changes in isometric force- 34. Young, WB, Wilson, GJ, and Byrne, C. A comparison of drop and relaxation-time, electromyographic and muscle fibre charac- jump training methods: effects on leg extensor strength qualities teristics of human skeletal muscle during strength training and and jumping performance. Int J Sports Med 20: 295–303, detraining. Acta Physiol Scand 125: 573–585, 1985. 1999.

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