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1 Aim. The goal of this study was to determine reference values of explosive strength for Spanish professional athletes using a force platform. Reference values are displayed as a sportsindependent percentile distribution. Methods. A total of 323 elite male athletes (age: 20.38±4.65 years, body mass: 75.04±14.30 kg, height: ±14.18 cm) from different disciplines performed the following test: squat jump (SJ), countermovement jump (CMJ), Abalakov test (AB), drop jump (DJ) and repeated jumps (RJ). We calculated: relative peak power, relative peak force, maximal height, symmetry index, explosive index of strength, relative effective impulse, duration of jump, elastic capacity, eccentric time, action of arm, jump number, average height, intensity and fatigue index of force. Results. Significant differences were found among sports disciplines (P<0.05) in relative peak power, maximal height and relative effective impulse during the SJ, CMJ and AB tests. No significant differences were found among disciplines in DJ variables. In RJ, the main variable characterizing the disciplines analyzed was average height, which showed a significant negative association with athletics, soccer, volleyball and gymnastics. Conclusion. The results obtained suggest that a percentile table may be useful in assessing explosive strength in athletes, regardless of there being any reference values available for their sports discipline. Key words: Quadriceps Muscle - Male - Muscle strength - Sports. Explosive strength in the lower limbs is one of the main performance factors in many sports. In all sports, this variable is a assessed using a series of jump tests, as described in the literature available Corresponding author: R. A. Centeno-Prada, Physiology Exercise Department, Andalusia Centre of Sport Medicine, Glorieta Beatriz Manchón s/n, 41092, Seville, Spain. racenpra@gmail.com J SPORTS MED PHYS FITNESS 2015;55: Jump percentile: a proposal for evaluation of high level sportsmen R. A. 1, C. LÓPEZ 2, J. NARANJO-ORELLANA 3 1Physiology Exercise Department Andalusia Centre of Sport Medicine, Seville, Spain 2Biomechanics Department Andalusia Centre of Sport Medicine, Seville, Spain 3Physiology Department Pablo de Olavide University, Seville, Spain Bosco et al. 1, 2 evaluating different characteristics of explosive strength according to the type of jump performed. The results of the tests conducted in this study may be useful in assessing differences in performance among different sports. One of the main challenges of finding valid and reliable reference performance values is that different measuring devices are used in previous studies 3, 4 such as camcorders, marks on the wall, force and contact platforms, among others. We only found studies using dynamometric platforms 5-7 to assess explosive strength in a specific sport, 8-14 where results are not compared with those of other sport or season, 15 and that include a small number of athletes, and assessing the relationship between jump and exercise 16 or between performance and jump, or between jump and training, or any other factor influencing strength. 25 We only found studies using dynamometric platforms 5-7 to assess explosive strength in a specific sport In addition, these studies do not compare the results obtained with those obtained in other sport or season 15 and have a small sample size. On the other hand, previous studies assess the relationship between jump and exercise 16 or between jump and performance or between jump 464 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS May 2015

2 and training, or any other factor influencing strength. 25 The tests assessing strength with a dynamometric platform are useful in measuring a variety of variables (strength, velocity, power, resistance strength, eccentric time). Most tests depict the behavior of these variables, but they do not specify the relationship between variables and performance in each sport. Therefore, these variables cannot be exploited to improve performance in athletes. This study was necessary because: 1) there are only a few, scattered studies using a dynamometric platform, and they are focused only on a small variety of sports; 2) there are no studies establishing standardized reference percentiles of explosive strength that include a significant number of athletes, regardless of the sport; 3) it is difficult to determine reference percentiles for all sports; 4) providing a global reference percentile table would facilitate the assessment of individual performance, and specific percentiles would be assigned to the most frequently studied sports; 5) when an athlete is tested, you can know their position on the percentile table without having to perform a new study or a review of the existing literature on that specific sport. The main goal of this study was to assess explosive strength variables using percentiles applicable to any sport. The secondary goal of this study was to verify if performance profiles can be established for different sports through the analysis of percentiles. Participants Materials and methods Due to the variety of existing sports and disciplines and the need for references in a population with a high number of athletes, we tried to include all sport disciplines that can benefit from the analysis of strength variables. Athletes involved either in individual or team sports were asked to perform a series of jumps according to the recommendations of Bosco et al. 1, 2 The sample included elite athletes from different Andalusian sports federations and technification centers referred to the Andalusian Center of Sport Medicine (CAMD) of Seville between 2007 and 2009 for different reasons. At the end of 2009, 353 male athletes had been recruited (age: 20.38±4.65 years, body mass: 75.04±14.30 kg, height: ±14.18 cm) from 11 different sports disciplines (athletics, badminton, basketball, gymnastics, handball, football, kickboxing, rugby, football, tennis and volleyball). In the field of athletics only sprint athletes were included. The research protocol was explained to all participants. Informed consent was obtained from all athletes as established by the Declaration of Helsinki ( b3/). The study was approved by the CAMD Ethics Committee. Each participant underwent thorough physical examination, with special focus on potential musculoskeletal and neurological disorders. All participants were healthy. Testing procedure Explosive strength variables were assessed using a dynamometric platform (DINASCAN, Biomechanics Institute of Valencia, Valencia, Spain), four force sensors with strain gauge technology with a sampling frequency of 1000 Hz, and Sport Jump software (Biomechanics Institute of Valencia, Valencia, Spain), which measures explosive strength variables by the appropriate algorithms. All participants performed the series of jumps proposed by Bosco, 1, 2 which includes the squat jump (SJ), the countermovement jump (CMJ), the Abalakov test (AB) or jump allowing arm swinging, the drop jump (DJ) or jump from a 40-cm height and repeated jumps (RJ) for 15 or 30 seconds, depending on the sports discipline. Jumps were performed according to the technical protocol established 1, 2 for explosive strength to be correctly measured. Each participant performed three to eight explosive jumps as high as possible, with the knees flexed at 90 degrees, and hands resting on hips (except for AB). The physical variables analyzed during the jumps were: 1) relative peak power (RPP), in W/BW, which is the maximum power given by the rate at which performing work is done divided by the body weight of the subject; 2) relative peak force (RPF), in N/BW is determined byte maximum force on the vertical axis during the test divided by the body weight of the subject; 3) maximal height (MH), in cm, is the maximal height reached by the center of mass of the Vol No. 5 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 465

3 subject during the jump, calculated through the double integration method of the force record; 4) symmetry index (SI), in %: after the jump the center of mass displacement is calculated and expressed as a percentage of the center of mass before the jump; 5) explosive index of strength (EIS), in N/s: is the maximal force developed in minimal time in the vertical axis, which is estimated by dividing the maximum force by the time taken to produce this level of force; 6) relative effective impulse (REI), in N/(s BW): It is calculated as the area enclosed between the weight of the subject and the vertical curve of force values during counter motion and landing, and it is expressed in values relative to body weight; 7) duration of jump (DoJ) in ms; it is the time elapsed between the onset of motion and the takeoff; 8) elastic capacity (EC) in %: It is the difference between the height reached in the CMJ and the SJ jump expressed as a percentage; 9) eccentric time (ET) in ms: it is the time elapsed between the onset of counter-motion and the lowest position reached during the CMJ and ABK tests; 10) action of arm (AA) in %: it is the difference between the height attained in the Abalakov test and that attained in the CMJ test expressed as a percentage; 11) jump number (JN): number of jumps performed during the repeated jump (RJ) test; 12) average height (AH), in cm: mean of the maximal height reached in each jump during the RJ test; 13) intensity (I) in %: It is calculated as the ratio of the mean of the maximal heights attained during the first three or five jumps to the height reached in the CMJ test, expressed as a percentage of the latter, depending on the test interval -15 or 30 s, respectively; finally, 14) fatigue index of force (FIF) in %: It is calculated by Table I. Parameters performed in each kind of jump. dividing the mean of the height attained in the last three or five jumps by the mean height reached in the first three or five jumps (depending on the test intervals -15 or 30 s, respectively). It is expressed in percentages in the RJ test. If intensity is >90%, it is calculated by dividing the mean height attained in the jumps by the height attained in the CMJ jump. It is expressed in percentages. The values obtained for the variables in each jump are shown in Table I. Statistical analysis A descriptive study of the whole sample was performed. Mean values and standard deviation were calculated for all jumps grouped by sports discipline. Comparative analysis of samples was carried out by sports. To conduct statistical analysis, we used the SPSS version 15.0 for Windows. Normal distribution was tested by sports discipline by the Shapiro-Wilk test. Since normal distribution was not present in all cases, we used a non-parametric test to compare k-wise independent distributions by the Kruskal-Wallis test. Differences were considered significant if P<0.05. This method would allow us to identify the sports disciplines which values differed more significantly and determine positive and negative correlations. Finally, we would identify the specific performance profile for each sport. We performed the Bonferroni post-hoc test to determine in each jump the variable showing the most significant difference among the different sports. We considered relevant differences found with at least half the sports analyzed. Parameters SJ CMJ AB DJ RJ Relative power peak (W/BW) Relative force peak (N/BW) Maximal height (cm) Symmetry Index (%) Explosive Index of Strength (N/s) Relative effective impulse (N/s/BW) Duration of jump (ms) Eccentric time (ms) Elastic capacity (%) Action of arm (%) Jump number Average height (cm) Intensity (%) Fatigue Index of Force (%) 466 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS May 2015

4 Subsequently, a percentile distribution was generated for each of the variables analyzed in each jump using the totality of the tests performed. This way, we had global references to comparatively place a specific athlete or group of athletes of a particular sport on the table. Results Tables II, III display mean values for all the variables showing significant differences among SJ, CMJ, AB and RJ jumps, which were performed by all athletes grouped by sports discipline. No significant differences were found in DJ variables among sports. Table IV shows the percentiles for the variables analyzed in each jump, regardless of the sports discipline. Table II shows all variables that showed significant differences among sports in SJ, CMJ and Table II. Average data in SJ, CMJ and Abalakov, only parameters with significant differences. SPORT Nº RPP (W/ BW) AB jumps RPP, MH and EI. In the RJ test, significant differences were only found in AH (Table III). With respect to sports disciplines, we found a characteristic performance pattern in sprint athletes, and soccer and volleyball players, with high and significant values for RPP and MH in the SJ, CMJ and AB tests. We also observed a characteristic performance pattern with lower values in gymnastics in SJ, CMJ and AB jumps. However, although values were lower, differences were only significant for CMJ and MH in the AB test. As to EI, significant differences were found in the SJ, CMJ and AB tests among some sports, although the performance pattern is not the same in these sports. In RJ, the main variable characterizing the sports analyzed was AH, which showed a significant negative correlation with athletics, soccer, volleyball and gymnastics. SJ CMJ Abalakov jump RPF (N/ MH EIS RPP BW) (cm) (N/s/ (W/ RPF (N/ MH EIS RPP BW) BW) BW) (cm) (N/s/ (W/ RPF (N/ MH BW) BW) BW) (cm) Athletics * * 2.66* 58.10* * * * 4.21 Badminton Basketball Soccer * 27.41* 37.16* * 28.72* 46.50* * 4.07 Indoor soccer Gymnastics * 39.91* * 3.27* * 3.47 Kick boxing * Rugby Tennis * * Volleyball * * 2.61* * * * 4.20 *P<0.05. Table III. Data for repeated jumps. SPORTS N Jump Number AH (cm) FIF (%) Athletics * Badminton Basketball Soccer * Indoor soccer Gymnastics * Kick boxing Rugby Tennis Volleyball * *P<0.05. Vol No. 5 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 467 EIS (N/s/ BW)

5 Table IV. Male percentile. Discussion The main contribution of this study is the provision of a percentile table representing jumping performance variables with jumps made according to Bosco protocol that is valid for all sports disciplines. The most relevant finding was the identification of three clear performance profiles for three types of jump: power and height attained in SJ, CMJ and AB jumps, which clearly characterize the performance pattern of sprinters and soccer and volleyball players. In addition, soccer players show a clear difference in force relative to body weight in SJ and CMJ. It is difficult to compare the results of this study with those obtained in previous studies using force platforms because of the diversity and low number of variables assessed. Thus, in previous studies some Percentiles SJ RPP (W/BW) RPF (N/BW) MH SI (%) EIS (N/s) REI (N/s/BW) DoJ (ms) CMJ RPP (W/BW) RPF (N/BW) MH SI (%) EIS (N/s) REI (N/s/BW) ET (ms) DoJ (ms) EC (%) AB RPP (W/BW) RPF (N/BW) MH SI (%) EIS (N/s) REI (N/s/BW) ET (ms) AA (%) DJ RPP (W/BW) RPF (N/BW) MH IES (N/s) DoJ (ms) RJ NJ AH FIF (%) I (%) variables are expressed as absolute values, while others are expressed as values relative to body weight. In addition, each study applies a different protocol, includes different types of jumps, or has different goals. For example, in some cases the goal of the study is to assess the relationship between training and jump performance or determining explosive strength profiles 6-13, 26 in a specific sport, or assessing the association between performance and explosive strength by analyzing a limited number of variables, excluding some of the variables obtained in a dynamometric platform. The results of this study indicate that the athletes showing the highest RPP and MH values in SJ are sprinters, and soccer and volleyball players, while gymnasts yield lower although non-significant values. The maximal height attained by soccer play- 468 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS May 2015

6 ers 12, 15, 21, 23, 26 is similar to that reported in other studies 9, 17, 19 and greater 16, 24 as compared to that reported in other studies, probably due to the device or protocol employed. Additionally, there are no studies available on some of the sports included in this study such as badminton, kick-boxing and rugby using a force platform. The relative strength attained in SJ by soccer players is in agreement with that found in the literature reviewed. 9, 17 Regarding RPP, the values obtained are lower as compared to those reported in a previous study 17 and higher as compared those reported in other study 23 may be due to their sports category being different to that of our athletes. In CMJ, the high MH values obtained by soccer and volleyball players are similar, 7, 9 slightly lower, 15, 16, 18, 21, 24, 25 and higher 12, 13, 20, 23 as compared to those reported in other studies. The values obtained by gymnasts 22 are lower than those obtained in soccer and volleyball. These differences may be due to the fact that each test requires the use of different types of strength, whereas the same technical requirements were applied to all tests. In the AB test, sprinters, and soccer and volleyball players attained high RPP and MH values, while only gymnasts showed low MH values. There are only two studies assessing performance values obtained during AB tests, and the MH values reported are lower than those observed in this study. 7, 15 As to RJ, the highest AH values were obtained by sprinters (43.17±5.98 cm), volleyball (40.53±3.43 cm) and soccer players (38.66±4.16 cm), while the lowest AH values were obtained by gymnasts (29.05±4.80 cm); FIF was low 1, 2, 5 in 15-s tests (sprinters, gymnasts basketball, football and volleyball players) and normal in 30-s tests (badminton players, kick-boxers, rugby, soccer and tennis players). This study proposes the assessment of individual explosive strength using a percentile table. To use the percentile table in the assessment of individual athletes it is necessary to establish the percentile rank of those sports differing most significantly from other sports. Thus, if we use the percentile table to assess individual performance, we observe that RPP and MH values obtained in SJ by sprinters, and soccer and volleyball players are above the 75th percentile (P-75), as they had values above W/BW and cm, respectively, thus indicating their better RPP and MH performance in the SJ test. On the other hand, EI values obtained by sprinters and soccer and volleyball players in SJ were >P-75, while they were <P-10 (2.07 N/s/BW) for gymnasts, which is suggestive of a lower RPP and MH performance in the latter discipline. The RPP values attained by sprinters in CMJ were >P-75 (>53.28 W/BW), which is indicative of a very good performance. Soccer and volleyball players obtained RPP values >P-50 (>47.55 W/BW), which is indicative of a good performance, while performance was poor in gymnastics, as their RPP values were <P-10 (<40.04 W/BW). With respect to MH, the highest values were attained by sprinters, soccer and volleyball players, as values were >P-75 (45.70 cm), while the poorest performance was found in gymnasts, with MH values <P-10 (35.12 cm). The highest RPP and MH values in AB were observed in sprinters, volleyball and soccer players, with values >P-75 (>61.03 W/BW and >58.83 cm, respectively), while gymnasts showed a poor MH performance, with a value <P-10 (<43.63 cm). With respect to RJ, the best performance was found in sprinters and volleyball players, as values were >P-75 (40.35 cm), while the poorest performance was found in gymnasts, with MH values <P-5 (29.20 cm). Conclusions The information provided in this study is highly useful because: 1) it provides a tool for assessing explosive strength in any athlete, regardless of the sport; 2) it is useful for examining differences among sports and among athletes; 3) it allows to assess the evolution of athletes throughout a season or successive seasons, and 4) it is useful for determining the most remarkable explosive strength variables for each sport or athlete with respect to others. This study proposes the assessment of individual explosive strength based on the percentile distribution of all results obtained in the different jump tests by all athletes, regardless of the sport. Each athlete will be assigned a specific percentile rank that will be indicative of their fitness status. Thus, to assess their performance and/or evolution, we just have to compare their individual percentile Vol No. 5 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 469

7 rank with that of their sport or with their best percentile attained in the past. Further studies should be conducted on more sports disciplines and in female athletes. This way, the percentiles obtained would be more representative of the whole community of athletes. References 1. Bosco C, Luhtanen P, Komi PV. A simple method for measurement of mechanical power in jumping. Eur J Appl Physiol Occup Physiol 1983;50: Bosco C. The Bosco s Test. In: Paidotribo E, editor. Strength assessment with the Bosco s Test. Roma: Italian Society of Sports Science; p Ziv G, Lidor R. Vertical jump in female and male volleyball players: A review of observational and experimental studies. Scand J Med Sci Sports 2010;20: Ziv G, Lidor R. Vertical jump in female and male basketball players--a review of observational and experimental studies. J Sci Med Sport 2010;13: Gonzalez-Badillo JJ, Gorostiaga-Ayestarán E. Fundamentos biológicos sobre el desarrollo y la manifestación de la fuerza. Fundamentos del entrenamiento de la fuerza 1 ed. Barcelona: Inde Publicaciones; p Jidovtseffa B, Croninb J, Harrisb N, Quievre J. Mechanical comparison of eight vertical jump exercises. Comput Methods Biomech Biomed Engin 2010;13:2. 7. Viitasalo JT. Anthropometric and physical performance characteristics of male volleyball players. Can J Appl Sport Sci 1982;7: Centeno-Prada RA, Naranjo-Orellana J, Beas-Jiménez JdD, Viana- Montaner B, Gómez-Puerto JR, Da Silva-Grigoleto ME. Análisis del salto en plataforma dinamométrica en jugadores de balonmano. Arch Med Deporte 2008;125:9. 9. Centeno-Prada RA, Naranjo-Orellana J, Calero-Campos T, Orellana-González R, Sánchez-Valverde E. Valores de la fuerza obtenidos mediante plataforma dinamométrica en futbolistas profesionales. MD Revista Científica en Medicina del Deporte 2005;1: Ferragut C, Cortadellas J, Navarro J, Arteaga R, Calbet JA. Por qué saltan más los jugadores de voleibol. Arch Med Deporte 2002; Ostojic SM, Mazic S, Dikic N. Profiling in basketball: physical and physiological characteristics of elite players. J Strength Cond Res 2006;20: Stolen T, Chamari K, Castagna C, Wisloff U. Physiology of soccer: an update. Sports Med 2005;35: Wisloff U, Helgerud J, Hoff J. Strength and endurance of elite soccer players. Med Sci Sports Exerc 1998;30: Wong del P, Wong SH. Physiological profile of Asian elite youth soccer players. J Strength Cond Res 2009;23: Casajus JA. Seasonal variation in fitness variables in professional soccer players. J Sports Med Phys Fitness 2001;41: Oliver J, Armstrong N, Williams C. Changes in jump performance and muscle activity following soccer-specific exercise. J Sports Sci 2008;26: Chamari K, Hachana Y, Ahmed YB, Galy O, Sghaier F, Chatard JC et al. Field and laboratory testing in young elite soccer players. Br J Sports Med 2004;38: Kollias I, Panoutsakopoulos V, Papaiakovou G. Comparing jumping ability among athletes of various sports: vertical drop jumping from 60 centimeters. J Strength Cond Res 2004;18: Ostojic SM, Mazic S, Dikic N. Elite and nonelite soccer players: preseasonal physical and physiological characteristics. Res Sports Med 2004;12: Wisloff U, Castagna C, Helgerud J, Jones R, Hoff J. Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players. Br J Sports Med 2004;38: Chelly MS, Ghenem MA, Abid K, Hermassi S, Tabka Z, Shephard RJ. Effects of in-season short-term plyometric training program on leg power, jump- and sprint performance of soccer players. J Strength Cond Res 2010;24: Grande I, Sampedro J, Rivilla-García J, Bofill A, Hontoria M. Evolución y relación de la capacidad de salto y amortiguación en gimnastas de rítmica de alto nivel. Cuadernos de Psicología del Deporte 2010;10 (Supplement): McMillan K, Helgerud J, Macdonald R, Hoff J. Physiological adaptations to soccer specific endurance training in professional youth soccer players. Br J Sports Med 2005;39: 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. J Strength Cond Res 2008;22: Hasson CJ, Dugan EL, Doyle TL, Humphries B, Newton RU. Neuromechanical strategies employed to increase jump height during the initiation of the squat jump. J Electromyogr Kinesiol 2004;14: Wong PL, Chamari K, Dellal A, Wisloff U. Relationship between anthropometric and physiological characteristics in youth soccer players. J Strength Cond Res 2009;23: Funding. This paper is part of a research project funded by a grant awarded by the Dirección General de Investigación del Ministerio de Ciencia e Innovación of Spain ( ). Acknowledgements. The Andalusian Centre of Sport Medicine (Andalusian Government Spain) has supported all technical devices for every measurement. All sportsmen participating in this study were attended in this Centre. The authors thank to Doctor Beas-Jiménez, from Andalusian Centre of Sport Medicine, for his contribution in the revision of data and final manuscript. Conflicts of interest. The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript. Received on May 13, Accepted for publication on February 12, THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS May 2015