For many sporting activities, such as tennis, squash, KINETIC AND KINEMATIC ASSOCIATIONS BETWEEN VERTICAL JUMP PERFORMANCE AND 10-M SPRINT TIME

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1 RESEARCH NOTE KINETIC AND KINEMATIC ASSOCIATIONS BETWEEN VERTICAL JUMP PERFORMANCE AND 10-M SPRINT TIME MÁRIO C. MARQUES 1,2 AND MIKEL IZQUIERDO 3 1 Department of Exercise Science, University of Beira Interior, Covilha, Portugal; 2 Research Center for Sport, Health and Human Development, Covilha, Portugal; and 3 Department of Health Sciences, Public University of Navarre, Navarre, Spain ABSTRACT Marques, MC and Izquierdo, M. Kinetic and kinematic associations between vertical jump performance and 10-m sprint time. J Strength Cond Res 28(8): , 2014 Implementing objective methods to assess physical performance has become an invaluable component of athlete or player development, monitoring, and talent identification in distinct sports. Many sports depend heavily upon muscular strength, muscle power output, and sprint performance, especially at competition level. Therefore, aim of this study was to examine relationships between 10-m time and several kinetic and kinematic parameters variables related to a weighted countermovement jump using a linear transducer in a large sample of trained sportsmen. A group of 32 trained sportsmen volunteered to participate in study (mean 6 SD: age years, body mass kg, body height m). The major findings of this study were significant associations between 10-m sprint time and peak velocity during jumping (r = 0.630; p, 0.01); and also nonsignificant associations between sprint and of force, mechanical impulse and rate of force development. These results underline important relationship between 10-m sprint and maximal lower-body strength, as assessed by force, power, and bar velocity displacement. It is suggested that sprinting time performance would benefit from training regimens aimed to improve se performance qualities. KEY WORDS lower extremity, force, power, sprinting, bar velocity INTRODUCTION For many sporting activities, such as tennis, squash, basketball, and soccer, athletes never attain maximum speed during sprinting. In fact, sprints most frequently occur over very short distances Address correspondence to Mikel Izquierdo, mikel.izquierdo@gmail. com. 28(8)/ Ó 2014 National Strength and Conditioning Association (0 10 m) from both standing and rolling starts. Consequently, speed over first steps and ability to accelerate quickly would be considered of greater importance (14,20). On this concern, research has found that first few ground contact phases of a short sprint are dominated by propulsive forces and by concentric muscle actions (2,3,16,17). Despite attention given to performance assessment by sports scientists, re is a paucity of research examining relationships between various motor skills, such as sprinting and jumping (15). Research has reported ambiguous results in relations observed between distinct strength measurements and sprint performance (8,11,13,23). Although some studies have claimed significant correlations between lower-body muscle strength measures and sprint performance (22), ors have not (6). These conflicting results may be result of fact that sprinting involves multiple-joint motions with precise coordination between various muscle groups, which is not adequately assessed by single joint tests that isolate muscles. Thus, relative importance of various lower-body muscle groups to sprinting performance is not totally clear (8,10,13), especially when short sprint is considered. Neverless, because explosive muscle actions are of major importance to short sprint acceleration (19), it seems logical that similar resistance training exercises might be suitable for testing and training se neuromuscular capacities. Yet, few studies have examined relationships between short sprint (,40 m) performance in trained subjects with force parameters, mechanical impulse, and mechanical power during muscle contractions of lower extremity during countermovement jumps (CMJ). In fact, understanding and developing sports speed would seem essential, given importance of first-step quickness and acceleration to many sports (20). These findings emphasize importance of concentric phase during initial acceleration, and role of propulsive force developed during first foot contacts of sprint in maximizing initial running velocity. None of previous studies examined short sprinting time (10 m) with dynamic force performance toger with power output, mechanical impulse, displacement, time, and bar velocity measured with a liner transducer in a large 2366 Copyright National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

2 sample of trained athletes. To best of our knowledge, only Marques et al. (14) examined short sprinting (5 m) with distinct strength metrics measured with a liner transducer, but in a small sample of physical students. An important relationship was found between 5-m sprint and maximal lower-body strength, as assessed by force, power, and bar velocity displacement. It is suggested that sprinting time performance would benefit from training regimens aimed to improve se performance qualities. In fact, re is a paucity of research that has examined relationships between short sprint (,20 m) performance in a sample of trained subjects and force parameters, mechanical impulse, mechanical power, and bar velocity outputs during muscle contractions of lower extremity in CMJ. Most of investigations have used isokinetic and isometric tests as indices of strength, but single joint actions are not specific assessment strategies (1). The CMJ exercise was chosen because it seems to mimic short sprinting technique (15,20). Thus, using a multi-joint exercise such as a CMJ test should be advantageous when exploring relationships with a dynamic movement such as sprinting. None of previous studies examined a 10-m sprint time with different strength metrics toger with power output and bar velocity during a loaded CMJ in a large sample of trained male sportsmen. A force platform would seem to be one of most commonly used measuring devices in sport biomechanics to access lower-body strength (4). However, some problems of using a force platform are cost and portability due to weight, which makes it difficult to use in field tests. To avoid se problems, a linear transducer could be used because this device can directly measure position over time. Furrmore, linear transducer has shown high validity and reliability in measurements of force compared with a force platform (7). Because explosive concentric muscle actions dominate sprint starts, it seems logical that similar resistance training movements might be suitable for testing and training se neuromuscular qualities. Consequently, relationship was examined between kinetics of a weighted explosive vertical jump exercise and sprint start performance, with a view to assessing wher or not such exercise should be recommended for individuals wishing to improve sprint acceleration. Therefore, aim of this research was to examine associations between 10-m time and distinct strength metrics of CMJ using a linear transducer in a large sample of trained athletes. Examination of se relationships could be of great importance for optimal development of resistance training programs to improve short sprint performance in athletes. It was hyposized that power and force would be significantly related to sprint time and also high bar velocity would show significant relationships to better sprint performance. METHODS Experimental Approach to Problem After a standard warm-up, participants performed 3 maximal CMJ trials in a Smith machine. The bar of this apparatus had a linear transducer attached (T-FORCE, Murcia, Spain). The rotary encoder of linear transducer recorded position and direction of bar (weighted 17 kg) to within an accuracy of m. Peak instantaneous power was calculated by product of velocity taken with linear transducer. Only concentric portion of CMJ was taken for analysis. Vertical instantaneous velocity (v) was directly measured by device and sampled at a frequency of 1 khz. The linear transducer was interfaced with a personal computer by means of a 14-bit resolution analog-to-digital data acquisition board, where a specialized software (T-FORCE Dynamic Measurement System) application automatically calculates relevant kinematic and kinetic parameters of every jump, provides real-time information on screen, and registers all data on disk for subsequent analysis. The derived mechanical variables were calculated by software as follows: displacement was obtained by integration of v data with respect to time; instantaneous acceleration (a) was obtained from differentiation of v with respect to time; instantaneous force (F) was calculated as F = m (a + g), where m is moving mass (in kg) that must be manually entered into software for each set, and g is acceleration due to gravity (being 9.81 m$s 22 ); instantaneous power output resulted from product of vertical applied force and bar velocity (P = F$v). Eccentric (negative v) and concentric (positive v) phases of movement were automatically detected. In CMJ, concentric phase was defined from moment following end of eccentric phase to point where peak velocity is reached (which takes place some milliseconds before takeoff from ground). Because effect of friction force was negligible in pilot testing, it was not taken into consideration in calculations. Similarly excluded from consideration was constant downward force exerted by cable because it was minimal compared with weight being lifted. The validity and reliability of this system have been previously established (9). The coefficient of variation (CV) ranged from 3.6 to 17%, with values being greater for rate of force development (RFD) measures, whereas intraclass coefficient correlation (ICC) values ranged from 0.93 to 0.98 with lowest value being recorded for RFD at peak force. Subjects A group of 32 male trained subjects volunteered to participate in study (mean 6 SD: age years, body mass kg, body height m). All participants were sports science students who were previously familiarized with all test procedures 4 weeks before measurements were applied. All were trained amateur athletes of different sports (e.g., soccer, futsal, track and field, and team handball). Consequently, all participants were well conditioned once y could squat 2 times ir body mass. Subjects were also familiar with all of testing procedures and exercises, as y had been performing m as part of ir regular training routine. Before commencing study, subjects had a physical examination, and each was VOLUME 28 NUMBER 8 AUGUST

3 10-m Sprint and Maximal Lower-Body Strength cleared of any medical disorders that might limit full participation in investigation. Subjects were required to sign an informed consent form before study. The study was conducted according to Declaration of Helsinki and was approved by institutional review boards of University of Beira Interior and Research Center in Sports, Health and Human Development, Portugal. Experimental Procedures Each participant initiated CMJ from a standing position, performed a crouching action followed immediately by a jump for maximal height. Hands remained on bar for entire movement to maintain contact between bar and shoulders. Three minutes of rest was provided between each trial to minimize fatigue. The trial-to-trial reliability of CMJ measured by linear transducer gave an ICC of for concentric force, maximum power, and maximum RFD. The mean and peak bar velocity ICCs were 0.91 and 0.93, respectively. The CV were 4 10% with linear transducer. Only best attempt was taken for analysis. For sprint testing, subjects were required to perform 3 maximum effort sprints of 10 m. Times were recorded using Brower equipment (Wireless Sprint System, Draper, UT, USA). Subjects performed sprints with 3-minute rest periods. Only best attempt was considered. The sprints reported an ICC of and CV of 1.6%. Statistical Analyses Mean (6SD) values were calculated for each variable. The normality and homoscedasticity assumptions were checked, respectively, with Shapiro-Wilk and Levene tests. The ICC was used to determine between-subject reliability of jumping tests. Within-subject variations for all tests were determined by calculating CV as outlined by Hopkins (12). Pearson product-moment correlation coefficient was used to verify association between variables. The level of significance was set at p # RESULTS Sprint performance variables and CMJ mechanical parameters are presented in Table 1. Pearson product-moment correlation coefficients between 10-m sprint performance and strength metrics of CMJ are presented in Table 2. A moderate relationship was observed between several kinetic and kinematic jumping parameters and 10-m sprint time (range, r = to 2636; p # 0.05). More noticeable was significant predictive value of peak bar velocity and sprint performance (r = ; p, 0.01) to sprint performance. Nonsignificant relationships were observed between mechanical impulse, RFD, and sprint time. DISCUSSION The aim of this study was to examine associations between short sprint performance and multiple kinematics and kinetic variables during a vertical jump in a sample of TABLE 1. Mean 6 SD results of different variables collected during sprint and countermovement jump.* Variables Mean 6 SD 10-m sprint, s Time to peak bar velocity, ms Mean bar velocity, m$s Peak bar velocity, m$s Mean force, N Mean force until peak velocity, N Peak force, N Time to peak force, ms Mechanical impulse, N$s RFD max,n$s Time to RFD max, ms Mean power, W Mean power until peak velocity, W Peak power, W Time to peak power, m$s *RFD = rate of force development. male trained subjects. To our best knowledge, this is first study to attempt examination of this issue with so much extent strength metrics measured with both a force platform and a linear transducer that can better explain 10-m sprint TABLE 2. Correlations between 10-m sprint performance and strength metrics of countermovement jumps using a linear transducer.* Variables r Values Time to peak bar velocity, ms z Mean bar velocity, m$s z Peak bar velocity, m$s z Mean force, N NS Mean force until peak velocity, N Peak force, N z Time to peak force, ms NS Mechanical impulse, N$s NS RFD max,n$s NS NS Time to RFD max, ms Mean power, W 0.579z Mean power until peak velocity, W 0.589z Peak power, W 0.636z Time to peak power, m$s NS *NS = nonsignificant; RFD = rate of force development. p # 0.05; zp,

4 performance in a group of trained athletes as one presented here. The major findings of current experiment were significant associations between 10-m sprint time and peak velocity (r = ; p, 0.01) as well as nonsignificant predictive value of mean force, mechanical impulse, and RFD. It may be suggested that peak bar velocity is an important factor to consider to develop short sprint performance in trained athletes. In a previous study, Sleivert and Taingahue (20) examined relationships between squat exercise and sprint performance. The authors observed a weak but significant correlation (r = ; p # 0.05) between bar velocity and 5-m performance. However, peak bar velocity used by Sleivert and Taingahue (20) corresponded to 30% of 1 repetition maximum during a traditional squat and not a stretch shorting movement such as one presented here. Similar to present study, but focused in upper extremity muscles, Gorostiaga et al. (10) observed a significant relationship between bar velocity during a bench press test using 30% of maximal load and standing ball throwing velocity for elite (r = 0.67) and amateur team handball players (r = 0.71). This value is very similar to one that was found in current study. Neverless, Marques et al. (14) failed to observe any significant association between 5-m sprint times and mean propulsive velocity and also peak velocity. Taken toger, se data suggest that sprinting performance may be related to capacity to move light external loads with lower limbs at maximal velocities. The sports science literature reported several studies that claimed significant correlations between force and sprint times (19), although ors have failed to report such results (13,15). These discrepancies could be because of fact that sprinting is a complex ability (2,3,8) that requires proper motor coordination between joints and muscles. Sprinting performance over very short distances (e.g., 10 m) is considered by many to require specific strength qualities and training techniques (2). It is well accepted that shorter sprints require a greater contribution of concentric muscle contractions and knee extensor activity (21). Young et al. (23) investigated relationship between force measures (Smith Machine squat jump with a 19 kg bar load from a 1208 knee angle) and sprinting performance of 20 elite junior track and field athletes. The best predictors of starting performance (time to 2.5 m) included force relative to body weight generated after 100 milliseconds from start of concentric jump movement (r = 0.73) and peak force (r = 0.72). Using a similar methodology, Wilson et al. (21) were able to observe that force at 30 milliseconds in a concentric squat jump was significantly correlated to sprint performance (r = 0.62). Or studies (21,23) also indicated that strength qualities such as RFD or force applied at 100 milliseconds may be more important than maximal strength. Nesser et al. (19) reported significant correlations between 40-m sprint time and peak isokinetic torque at a speed of 7.85 rad$s 21 for hip and knee extensors and knee flexors (r = to 20.61). However, more recently, we (14) failed to show significant correlations between maximum RFD and sprint times but also between times to maximum rate of force with 5-m sprint performance. The present results, refore, support what little has been reported in literature and indicate that development of peak force plays a larger role. Vertical impulse has been defined as an important determinant factor of sprinting ability. Wilson et al. (21) investigated relationship between impulse developed in first 100 milliseconds of a concentric squat jump (unloaded) and sprinting ability over 30 m. Although reported as nonsignificant, y reveal a moderate correlation (r = 20.49) between impulse at 1508 and sprinting ability. Interestingly, relationship between impulse at 1108 and sprint ability was low (r = 0.06, NS). Perhaps influence of starting knee angle is critical to relationship between concentric only machine squat jump strength measures and sprint ability. It may be hyposized that length-tension relationship of hip and knee extensors at lower starting knee angles is biomechanically less specific to actual knee angles encountered in 10-m sprints. Our study corroborates findings reported by Wilson et al. (21) showing that impulse is not a strong parameter in predicting sprinting time over short sprints. Therefore, a certain discrepancy should be expected between CMJ impulse measure and 10-m performance obtained. It should be kept in mind that sample used by or studies comprised subjects of different sports, levels, and genders, which may account for variation in results as compared with our study. The RFD has been one of most important variables to explain performance in activities where great acceleration is required (18). This can be related to fact that greater RFD, higher power will be and force generated against same load. In most sports activities, RFD is strongly related to performance abilities, such as sprinting, in which force production time is very small. A previously published report examining relationship between RFD and sprint performance have provided equivocal findings, with some studies reporting a significant relationship and ors failing to observe a positive association (18). The present study failed to indicate a significant association between different rates of force measurement and 10-m sprint time. It is difficult to compare results of se studies because y differ markedly in a number of factors, including method of measurement. Yet, variations in correlation coefficients may have been explained by differences in reliability for measuring peak RFD (CV = 6 12%) when compared with measuring peak force (CV = 4 10%). An important amount of scientific literature focuses ir attention on clarifying relationship between mechanical power output and athletic performance (9). A concern raised by this literature is that power measurements and protocols used in se studies can vary considerably (5). Along same line, Carlock et al. (4) stated that making VOLUME 28 NUMBER 8 AUGUST

5 10-m Sprint and Maximal Lower-Body Strength comparisons between various studies is rar difficult because re are different exercises being used to measure peak power output. Despite se limitations, re is a growing body of knowledge on relationship of power to sprint performance. Most researchers have found moderate to strong correlations between jump height (and/or relative peak power), measured during a vertical jump, and sprinting performance (11). Theoretically, re should be a significant relationship between se parameters, as a rapid stretch shortening cycle occurs both in jumping and sprinting. The present study indicated that peak power could explain approximately 36% of sprint performance. Sleivert and Taingahue (20) who investigated relationship between 5-m sprint times and power variables in trained athletes could observe that both mean power and peak power relative to body mass were to a moderate degree negatively correlated with 5-m sprint time (r = to 0.68). Unfortunately, authors chose not to incorporate body mass into equation of force, asserting that it is not strictly mechanically correct to do so. The authors (20) noted that not using system mass has effect of markedly reducing power outputs and altering point on power. Cronin and Hansen (6) noticed that peak power output measured on a force platform in squat jump (expressed relative to subject s body mass) was found to be related to 5-m (r = 20.55; p # 0.05) and 10-m (r = 20.54; p # 0.05) sprint times. These findings highlight important relationship between 10-m sprint and maximal lower-body strength, as assessed by force, power, and bar velocity. This research possessed some limitation that should be considered. First, this study used a sample of well-trained subjects but not elite athletes. Second, one could speculate about testing of lower body is conducted using a jump squat movement in an apparatus involving a barbell attached to vertical supports (Smith Machine apparatus). As a result, Smith machine restricts movement of barbell to vertical plane and potentially decreases variability in performing movement. However, this assumption is yet to be investigated. Furrmore, we only assessed lower-body kinetics and not kinetics variables playing an important role in short sprint performance. Given fact that sprinting is a highly complex motor skill, it would be unlikely to find a single test that accounts for nearly all of variability in sprinting. Finally, it should be also noted that correlations can only give insights into associations and not into cause and effect. Therefore, practical applications described herewith need to be interpreted with this in mind. In terms of isoinertial assessment or any assessment for that matter, strength and conditioning practitioner or scientist must be cautious in describing relationships between variables. As observed in this study, relationship between CMJ mechanical parameters (i.e., velocity, force, and power) and sprint performance was found to differ according to each selected variable. This has important implications for correlational research in that nonsignificant relationships between movements may be reported, when actually it is measure and not movement that are unrelated. Based on current results, it possible that peak bar velocity is an important factor to consider to develop short sprint performance in trained athletes. Thus, it is suggested that sprinting time performance would benefit from training regimens aimed to improve se performance qualities. Moreover, great majority of research uses acyclic vertical type movements (e.g., squat, vertical jumps) to predict an activity that is cyclic and horizontal in nature. Furr research may benefit from investigating movements that require greater horizontal force production. PRACTICAL APPLICATIONS Improvement in short distance sprint ability is a major training goal for many sports, and countermovement jumping is a well-recognized training exercise used to achieve this. In individual sports like basketball, soccer, or team handball, for example, athletes must improve sprint performance over very short distances to achieve better personal specific performances. In fact, a team sport athlete must sprint than his or her opponent. These findings should be interpreted with caution because correlations do not signify causation, so additional research is required to clarify wher improvements in upper-body strength, velocity, or power as a result of resistance and/or plyometric training will indeed improve jumping ability in trained track and field athletes. Coaches often express need to have access to an easily administered test that will allow assessment of athlete without actually measuring sports performance. This study represents one approach to assessing physical state of elite team sports athletes that might satisfy this need. ACKNOWLEDGMENT We thank dedicated group subjects who participated in this study. REFERENCES 1. Abernethy, P, Wilson, G, and Logan, P. Strength and power assessment: Issues, controversies and challenges. Sports Med 19: , Bezodis, NE, Salo, IT, and Trewartha, G. Choice of sprint start performance measure affects performance-based ranking within a group of sprinters: Which is most appropriate measure? Sport Biomech 9: , Bracic, M, Supej, M, Peharec, S, Bacic, P, and Coh, M. An investigation of influence of bilateral deficit on countermovement jump performance in elite sprinters. Kinesiology 4: 73 81, Carlock, JM, Smith, SL, Hartman, MJ, Morris, RT, Ciroslan, DA, Pierce, KC, Newton, RU, Harman, EA, Sands, WA, and Stone, MH. The relationship between vertical jump power estimates and weightlifting ability: A field-test approach. 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