ISMJ International SportMed Journal Original research article Force plate vertical jump measurements and 30 m sprint performance in trained athletes: A short report * 1,2 Professor Mário C Marques, PhD, 3 Professor Mikel Izquierdo, PhD, 1,2 Professor Ricardo Ferraz, MSc, 4 Professor André L Carneiro, PhD, 5 Professor Juan José González-Badillo, PhD 1 Department of Exercise Science, University of Beira Interior, Covilhã, Portugal 2 Research Centre for Sport, Health and Human Development, Vila Real, Portugal 3 Public University of Navarre, Navarre, Spain 4 University of Montes Claros, Department of Sport Sciences, Unimontes, Brazil 5 Department of Sports and Informatics, University of Pablo de Olavide, Seville, Spain *Corresponding author. Address at the end of the text. Abstract The aim of this study was to examine the relationships between short sprint time (30 metres) and several kinetic variables of the countermovement jump (CMJ) in a sample of trained athletes. A group of 12 trained athletes volunteered to participate in the study (mean ± SD: age 22.2 ± 1.2 years, body mass 67.5 ± 5.5 kg, body height 1.75 ± 0.02 m). Following a standard warm-up, participants performed three maximal CMJ trials on a Smith machine and three maximum effort sprints of 30 metres. The major findings of this study were the significant associations between 30 metre sprint time and the concentric phase of CMJ for both force and power parameters. In addition, non-significant predictive values were observed between sprint performance time and jump impulse values. The results are of practical interest for optimising training and assessment methods in sprint performance. Keywords: lower extremity, force, power, velocity, sprinting *Professor Mário C Marques, PhD Dr Marques is a professor in the Department of Exercise Science, University of Beira Interior, Covilhã, Portugal and the Research Centre for Sport, Health and Human Development, Vila Real, Portugal. His main research interests are performance evaluation, namely in strength and power training in elite athletes. Professor Mikel Izquierdo, PhD Dr Izquierdo is a professor in the Department of Health Sciences, Public University of Navarre, Navarre, Spain. His main research interests are biomechanics and neuromuscular issues in strength and power training. Email: mikel.izquierdo@gmail.com Professor Ricardo Ferraz, MSc Professor Ferraz is a PhD candidate and a professor in the Department of Exercise Science, University of Beira Interior, Covilhã, Portugal and the Research Centre for Sport, Health and Human Development, Vila Real, Portugal. His main research interests are performance evaluation, namely in strength and power training in soccer players. Email: ricardo ferraz@hotmail.com 77 Official Journal of FIMS (International Federation of Sports Medicine)
Professor André L Carneiro, PhD Dr Carneiro is a professor in the Department of Department of Sport Sciences, Unimontes University, Unimontes, Brasil. His main research interests are strength and power training. Email: algcarneiro@hotmail.com Professor Juan J González-Badillo, PhD Dr González-Badillo is a professor in the Department of Sports and Informatics, University of Pablo de Olavide, Seville, Spain. His main research interests are performance evaluation, namely in strength and power training in elite athletes. Email: jjgbadi@gmail.com Introduction Associations between distinct kinematic and kinetic variables attained during the vertical jump and sprint performance have focused scientific and practical interest 1,2. In fact, sprinting ability has biomechanical, kinematic and muscle performance factors similar to the vertical jump movement. Several assessment approaches have used different stretch shortening cycle tests (i.e. countermovement jump, drop jumps), a wide range of velocities and joints in isokinetic tests (i.e. 30 º to 240º s -1 ), as well as different isometric testing joints (from 90º to 120º) and biomechanical assessment techniques 3. In addition, much research has indicated significant correlations between sprinting performance over various distances and a range of measures of strength and power 4. However, associations between this complex motor task and short sprinting ability have produced equivocal results 5,6,7. For example, very strong correlations (r = -0.86; P<0.001) have been reported between sprint performance and a countermovement jump (CMJ) 2, whereas low to moderate correlations (ranging from r = 0.43 to 0.66; P<0.05) have been reported by other researchers between sprint performance and jump height ability from a CMJ and squat jump 5,8. In addition, few studies have examined the relationships between short sprint (< 40 m) performance in trained subjects with kinetic variables such as force, time, impulse and power during muscle contractions of the lowerextremity in a countermovement vertical jump (CMJ). Thus, identifying the predictive ability of more sensitive kinetic jump measures with sprint performance warrants further research for optimising jump training prescriptions for track and physical conditioning coaches. may be positively related to the maximum shortdistance sprint. The CMJ exercise was chosen because it seems to mimic the short sprinting technique 10. Thus, using a multi-joint exercise such as a CMJ test should be advantageous when exploring relationships with a dynamic movement such as sprinting. Identifying the predictive ability of more sensitive kinetic vertical jump variables with the short sprint may facilitate the development of optimal athletic conditioning programmes for improving short-distance sprint performance. Methods Participants Apart from normal daily practice sessions (2 3 hours per day timed for 16h00) and weekend competitions, all volunteers were involved in a 16- week resistance training programme. Two to three resistance training sessions were completed per week and included two maximal dynamic strength exercises (bench press and half squat) and three power exercises, such as power clean, snatch, and weighted countermovement jumps. Consequently, all the athletes were highly trained (mean ± SD: sprint: 4.05±0.29 m/s, age 22.2 ± 1.2 yrs., body mass 67.5 ± 5.5 kg, body height 1.75 ± 0.02 m) participated in the study. Before starting the study all participants underwent a physical examination and were cleared for any medical disorders that might limit full participation in the investigation. No athlete was found to be taking exogenous anabolic androgenic steroids or other drugs or substances likely to affect physical performance or hormonal balance. Prior to the implementation of any of the procedures, the research was submitted to the Research Ethics Committee involving human subjects and was unconditionally approved under protocol nº 0064/2007. The purpose of this study was to examine the associations between 30-metre sprint time and several kinetic variables involved in the CMJ Study design using a force plate with a sample of trained athletes. Since explosive muscle actions are of The present study used a cross-sectional major importance to short sprint acceleration 9 experimental design to examine the associations, it between the kinetic parameters during the CMJ can be hypothesised that kinetic jump measures, and sprint times in a group of trained male such as time, velocity, impulse, force and power, athletes. Participants were familiar with the testing 78 Official Journal of FIMS (International Federation of Sports Medicine)
procedures since the exercises involved constituted part of their normal training routine. Following a standardised warm-up, participants performed three maximal CMJ trials on a Smith machine while standing on a portable force platform (Isonet, JLML, Madrid, Spain). A linear positional transducer was attached to the bar of the Smith machine (Isocontrol, JLML, Madrid, Spain) and synchronised with the force platform. The force platform was connected to a portable computer and recorded data at a sample rate of 1000 Hz. The linear transducer recorded the position and direction of the bar to within an accuracy of 0.0002 m. Peak power was calculated by the product of velocity taken with the linear transducer and the ground reaction force measured by the portable force platform. Participants stood on the Smith machine and rested the bar (standard weighted: 17 kg) on their shoulders. Participants initiated the CMJ from a standing position, performed a crouching action followed immediately by a jump for maximal height. Hands remained holding on to the bar for the entire movement in order to maintain contact between the bar and shoulders. Three minutes of rest were provided between each trial to minimise the likelihood of fatigue. In order to locate the optimal relationship between sprint performance and CMJ kinetic variables, jumping performance was divided into three different phases (Figure 1): 1) the eccentric phase, defined from the initiation of movement until maximum negative velocity occurred (i.e. the centre of mass acceleration is 0 m s -2 ), the transition phase, defined from the moment following maximum negative velocity until the end of the eccentric phase where velocity is 0m/s; and 3), and the concentric phase, defined from the moment following the end of the eccentric phase until maximal positive velocity was achieved. The trial-to-trial reliability of the CMJ measured by the force platform gave an average for the intraclass correlation coefficient (ICC) of 0.87-0.97. The average values for the coefficient of variation (CV) were 5.8-9.9%. For sprint testing subjects were required to perform three maximal effort sprints of 30 metres. Times were recorded using Brower equipment (Wireless Sprint System, USA). Subjects performed trial sprints separated by 3 minutes of rest, of which only the best attempt was considered. The sprint reported ICCs of 0.94-0.99 and CVs of 1.2-2.4% respectively. Figure 1: Countermovement jump phases Statistical analysis outlined by Hopkins 11. Pearson product-moment Mean (± SD) was calculated for each variable. correlation coefficient was used to verify the The Kolmogorov-Smirnov test of normality and association between variables. The level of Levine's test of homogeneity of variance were significance was set at p 0.05. performed to verify the normality of the distribution. The intraclass correlation coefficient Results (ICC) was used to determine between-subject The Pearson product moment correlation reliability of the jumping tests. Within-subject coefficients between 30 metre sprint performance variation for all tests was determined by and kinetic variables of the CMJ are presented in calculating the coefficient of variation (CV) as Table 1. Significant associations between 30 79 Official Journal of FIMS (International Federation of Sports Medicine)
metre sprint time and both force and power parameters were observed during the concentric phase of the countermovement jump (ranging from r= -0.86 r= - 0.91; P<0.01). In contrast, nonsignificant predictive values were observed between sprint performance time and impulse values, amongst all three jumping phases. Table 1: Correlations (r) between CMJ kinetic parameters and 30 metre sprint times Variables Mean (±SD) r p value Eccentric Time (ms) 508.66 ± 89.05 0.430 NS p= 0.248 Concentric Time (ms) 275.88 ± 31.48 0.688* p= 0.040 Eccentric/Concentric Time (ms) 2.57 ± 0.25-0.227 NS p= 0.557 Eccentric Impulse (N. s) 17484.38±3941.53-0.521 NS p= 0.179 Transition Impulse (N. s) 9063.22±1868.98-0.041 NS p= 0.330 Concentric Impulse (N. s) 32383.93±7395.18-0.432 NS p= 0.191 Eccentric Peak Force (N) 114.88±78.61-0.526 NS p= 0.133 Transition Peak Force (N) 906.44±263.81-0.896** p= 0.001 Concentric Peak Force (N) 997.51±210.49-0.859** p= 0.003 Eccentric Peak Power (W) 557.49±208.38-0.426 NS p= 0.098 Transition Peak Power (W) 12.96±4.81-0.688 * p= 0.041 Concentric Peak Power (W) 2219.20±453.12-0.890** p= 0.001 Eccentric Average Power (W) 146.09±50.70-0.457 NS p= 0.663 Transition Average Power (W) 520.31±213.14-0.661 NS p= 0.117 Concentric average power (W) 1166.31±311.11-0.912** p= 0.001 Maximum Positive Velocity (m/s) 1.66±0.27-0.353 NS p= 0.251 Maximum Negative Velocity (m/s) 2.95±0.22-0.206 NS p=0.221 Significance: **p<0.01; *p<0.05; NS: non-significant Discussion and conclusions A greater understanding of the requirements of short sprint performance is crucial before effective testing, monitoring and optimised training methods can be developed. A unique purpose of this study was to examine the associations between short sprint ability and several kinetic variables during a vertical jump that can better explain short sprint performance in a sample of trained subjects. The major findings of this study were the significant associations between the 30 metre sprint time and both force and power parameters reached during the concentric phase of the countermovement jump. In contrast, nonsignificant predictive values were observed between the impulse values reached during eccentric, transition and concentric jumping phases and sprint performance. Because the current study was performed with instrumental rigor and with high reliability coefficients in different variables in a group of trained men, the results are of practical interest in optimising training and assessment methods in sprint performance. Time The data observed in this study showed that times for both eccentric and eccentric/concentric countermovement jump phases were not significantly associated with the 30 metre sprint time. No previous study has attempted to examine these associations. González-Badillo and 80 Official Journal of FIMS (International Federation of Sports Medicine)
Marques 12 showed that both eccentric and concentric times were poor indicators of jump performance, since both explain approximately only 9-16 percent of the height reached in the CMJ. It appears that subjects who attained higher eccentric times tended to jump less. This may explain the lack of association between short sprint performance times among the vertical jump phases. Yet the current experiment was able to observe significant associations between concentric times and short sprint performance. In the first steps of sprint running, the propulsion (concentric action) phase has been reported to be around 81% of the total step duration 6. Consequently, it is no surprise that strong correlations (r= ~0.7) were revealed between CMJ concentric time and 30 metre sprint time in the present study. Impulse Vertical impulse during the concentric phase of the countermovement jumps has been biomechanically defined as an important parameter to explain sprinting ability. Here Wilson et al. 13 investigated the relationship between the impulse developed in the first 100 ms of a concentric squat jump (unloaded) and sprinting ability over 30 metres. Although reported as nonsignificant, they revealed a moderate correlation (r =-0.49) between impulse at 150 and sprinting ability. Interestingly, the relationship between impulse at 110 and sprint ability was low (r = 0.06). The influence of the starting knee angle was possibly a critical factor to explain the relationship between concentric-only machine squat-jump strength measures and sprint ability. It is also likely that the length-tension relationship of the hip and knee extensors at lower starting knee angles is biomechanically less specific to the actual knee angles encountered in 30 metre sprints. To examine the relationship between short sprinting (30 and 40 metres) and kinetic measures during the eccentric-only CMJ performance in elite track and field athletes, Dias et al. 14 found significant associations between sprints and peak force (r= -0.91; p<0.01), average power (r= - 0.688; p<0.05), but failed to observe significant correlations between sprint times and peak power and impulse. These results contrast with the findings of the current study, except for the impulse parameter. On the other hand, the present study corroborates the findings reported by Wilson et al. 13 showing that impulse is not a vital parameter in predicting sprinting time over short sprints. However, it should be remembered that this present study s sample comprised subjects from different sports, which may account for the variation in results. Therefore a certain discrepancy should be expected between the CMJ impulse measure and the 30 metre performance obtained. Furthermore, the samples used by other studies comprised subjects of different sports, levels, and genders, which may account for the variation in results as compared to this present study. In addition, sprint ability over short distances is considered by many researchers and practitioners to require specific strength qualities and hence training regimens. Force Different studies have claimed significant correlations between force and sprint time 9. In contrast, others 5,15 have failed to report similar results. These conflicting claims could be because sprinting is a complex ability 1,16 that requires proper motor coordination between joints and muscles. Sprinting ability over very short distances (e.g. 30 metres) is considered by many sports scientists to require specific strength qualities and training techniques. It is generally accepted that shorter sprints require a greater contribution of concentric muscle contractions and knee extensor activity. Young et al. 2 investigated the relationship between force measures (concentric-only Smith squat jump with a 19 kg bar load from a 120º knee angle) and sprinting performance of 20 elite junior track and field athletes. The best predictors of starting performance (time to 2.5 metres) included force relative to body weight generated after 100 ms from the start of the concentric jump movement (r = 0.73) and peak force (r = 0.72). Using a similar methodology, Wilson et al. 13 observed that force at 30 ms in a concentric squat jump was significantly correlated with sprint performance (r = 0.62) and able to effectively discriminate the good from the poor performers. Other studies 2,13 also indicate that force applied at 100 ms may be more important than maximal strength. Nesser et al. 9 reported significant associations between 40 metre sprint time and peak isokinetic torque at a speed of 7.85 rad/s for the hip and knee extensors and knee flexors (r=- 0.54 to - 0.61). Power Previous studies have tried to understand the relationship between mechanical power output and athletic performance 12. A concern raised by this literature is that the power measurements and protocols used in these studies can vary considerably 17. Similarly, Carlock et al. 4 stated that making comparisons between various studies is rather difficult because there are different exercises being used to measure peak power output. Yet, most researchers have found moderate to strong correlations between jump height (and/or relative peak power) measured during a vertical jump and short sprint ability 18. 81 Official Journal of FIMS (International Federation of Sports Medicine)
Theoretically, there should be a significant relationship between these parameters, as a rapid stretch shortening cycle occurs both in jumping and sprinting. The present study indicated that concentric power could explain approximately 81% of the sprint performance. Sleivert and Taingahue 10 who investigated the relationship between 5 metre sprint times and concentric power in a sample of trained athletes observed that both mean and peak power relative to body mass were to an important degree negatively correlated with 5 metre sprint time (r = - 0.64 to 0.68). The authors chose not to incorporate body mass (so-called system mass) into the equation of force, asserting that it is strictly not mechanically correct to do so. Sleivert and Taingahue 10 noted that not using system mass has the effect of markedly reducing power outputs and altering the point on the power. Cronin and Hansen 8 noticed that peak power output measured on a force platform in the squat jump (expressed relative to subject body mass) was found to be related to the 5 (r = - 0.55, p <0.05) and 10 metre sprint (r = - 0.54, p <0.05) times. In agreement with previous studies, therefore, these authors showed that power output amongst all CMJ phases is significantly associated with sprint ability. Velocity Unfortunately, no previous studies have examined simultaneously the relationships between negative and positive velocity during a weighted CMJ and short sprint performance. Sleivert and Taingahue 10 and Marques et al. 19, examined the relationship between positive bar velocity and 5 metre sprint. In contrast to this present study s results, both studies showed a poor but significant correlation (r= - 0.45/-47, p<0.05) between bar velocity and 5 metre performance. The peak bar velocity used by Sleivert and Taingahue 10, for example, corresponded to 30% of one maximum repetition during a traditional squat rather than a free jumping movement such as the one presented here. In addition, the moderate but significant correlation observed by Young et al. 2 was the second best result, immediately after the peak power output per body weight. The results reported by these authors 2,10 disagree with those observed in the present study. Taken together these data suggest that sprinting is related to the capacity to move light external loads with lower limbs at maximal positive velocities. Further, these differences can be partially explained by two factors. Sleivert and Taingahue 10 used a shorter distance (i.e. 10 metre) where the acceleration is crucial, whereas Young et al. 2 used a release sprint ability. Within the confines of this present study, these findings highlight the important relationship between the 30 metre sprint and maximal lower body strength, as assessed by the force and power parameters. This research had limitations that should be considered, such as the reduced n size, which may have an influence on correlations if outliers are present. Normality was assessed for each of the performance outcomes and it seems the results of this investigation were not affected by outliers. In addition, these authors assessed only lower body kinetics and kinematic variables were not considered due the limited role involved in short sprint performance. Given the fact that sprinting is a highly complex motor skill, it would be unlikely to find a single test that accounts for nearly all the variability in sprinting. It should be noted, however, that correlations can only give insights into associations and not into cause and effect; therefore, the practical applications described here need to be interpreted with this in mind. With isoinertial assessment (or any assessment for that matter) the strength and conditioning practitioner or scientist must be cautious in describing relationships between variables. As observed in this study, the relationship between isoinertial jump measures and sprint performance was found to differ according to whether the outcome variable was recorded. This has important implications for correlational research in that non-significant relationships between movements may be reported, when actually it is the measure and not the movement that is unrelated. Moreover, the great majority of research uses acyclic verticaltype movements (e.g. squat, vertical jumps) to predict an activity that is cyclical and horizontal in nature. Further research may benefit from investigating movements that require greater horizontal force production. Acknowledgement The authors thank the subjects who participated in this study. Address for corresponding author: Professor Mário C Marques, Sports Science Department, University of Beira Interior, Covilhã, Portugal Rua Marquês D Ávila e Bolama 6201-001 Covilhã Tel.: +00351275320690 Fax :+00351275320695 Email: mariomarques@mariomarques.com 82 Official Journal of FIMS (International Federation of Sports Medicine)
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