Sprint performance is an important determinant of playing ability for many sports, including soccer. Sprinting occurs with a unilateral stance phase with the primary objective to move horizontally. Therefore, to achieve specificity during training for sprint performance, exercises that include a unilateral stance while directing forces in the horizontal direction appear to be warranted. During soccer play, sprinting occurs primarily across short distances with accelerations beginning from static starts and at higher running speeds. As a result, the ability to accelerate at any speed and running for brief periods at top speed are important qualities for soccer performance. Along with sprint training, various jumping and plyometric exercises have been included into training programs to improve running velocity (25). Sprinting relies on the effective use of muscle stiffness during the stretch-shorten cycle (31), which has shown to be enhanced through jump and plyometric training (26,28). In comparison to the countermovement, the loading conditions on the stance leg during drop-jump exercises appear to be more similar to the loading conditions during sprinting. However, the most effective types of exercises involving jump training to improve the different phases of sprint performance (acceleration at different speeds and top speed) is yet to be clearly understood.
Both unilateral and bilateral jumps and plyometrics containing horizontal and vertical components are typically included in sprint training programs. These exercises are performed with a drop-landing sequence and from the floor using a countermovement. Sprinting is performed with a unilateral support phase that primarily includes horizontal and vertical impulse to produce motion. Previous research indicates that vertical ground reaction forces and vertical motion during running should be minimized to maximize horizontal motion (12). If the primary goal is to enhance horizontal motion while sprinting, it is logical to suggest that exercises requiring primarily a horizontally directed impulse and use of the stretch-shorten cycle would be most effective for improved sprint performance. Moreover, sprinting occurs with a unilateral stance to produce the impulse; however, research comparing the relationship between unilateral vs. bilateral jump tests and sprint performance is limited (17,18,20). It is likely that the unilateral jumps will produce a higher correlation with sprint performance because sprinting requires production of forces unilaterally. The methods from these previous studies are characterized by differences in subject type, jump test, sprint distance, and the variables analyzed, which warrants the need for further research. Research analyzing the relationship between various jumping and plyometric exercises and sprint performance will provide strength and conditioning specialists with information needed to select the most appropriate exercises to incorporate into their athletes' training programs.
There are also limited data comparing the relationship between vertical and horizontal jump tests and sprint performance within the same study (17,18,20,23). In addition, few studies have been conducted using highly competitive athletes (2,5,17,32,33), particularly, female athletes (9). Currently, previous research has not compared the relationship between vertical vs. horizontal jump tasks including unilateral and bilateral components and sprint performance in collegiate, female athletes.
Holm et al. (11) recently suggested that a better understanding of the relationship between the determinants of sprinting such as step length and frequency and jump performance would lend an insight into the specific exercises that may improve the different types of running speed. The product of step length and frequency determine sprinting ability. Specifically, improvement of step length has been suggested to improve early acceleration as long as step frequency stays the same or is not compromised to the same degree (12). Therefore, the purpose of this study was to investigate the relationship between kinematic measures of various vertical and horizontal jumps performed under unilateral and bilateral conditions and sprint time, step length, and step frequency measured during a 10- and 25-m sprint in female college soccer players. We hypothesized that the unilateral, horizontal jumps would produce the highest correlation with sprint performance as the kinematics appeared to be most similar between these tasks.
Experimental Approach to the Problem
The relationship between jump and sprint performance is not clearly understood because of limited data and differences in research designs and subject type. Several studies have been conducted to compare the relationship between various unilateral, bilateral, vertical, and horizontal jump tests and sprint performance, but few have included all of these tests in the same study. We included the unilateral and bilateral depth jumps and countermovement jumps in this study because these jumps are thought to improve sprint performance after training. The type of jump that has the highest correlation would indicate that this exercise should be emphasized during training to improve sprint performance. Sprinting requires unilateral loading and propulsion of forces on the stance leg directed primarily horizontally, which indicates that similar jumps may produce the highest correlation with sprinting. Research analyzing this relationship in female athletes is sparse (9,16); therefore, division I, women soccer players were recruited to volunteer for this study. Two sprint distances (10 and 25 m) were included as each measures different qualities of sprint performance that are important for soccer performance. Jump kinematics were included to better understand the type of jump and the specific variables measured from the jump that are related to the determinants of sprint performance. These data can be used to modify jump kinematics during training to improve specific factors determining sprint performance.
Fifteen National Collegiate Athletic Association (NCAA) mass 61.65 ± 7.7 kg, age 20.19 ± 0.91 years) volunteered to participate in this study. The subjects were screened for injuries that would affect sprint or jump performance. All subjects had a minimum of year of participation in a year-round strength and conditioning program. The study was conducted during the off-season after 4 weeks of active rest after the season and before starting an off-season training program. All subjects signed an inform consent document after the investigation was approved by the university's Institutional Review Board for the use of human subjects in research.
After a 5-minute jog and light lower-body stretching, a 10- and 25-m sprint test was administered within 1 session with a 5-minute rest period between tests. All subjects used a standing start with the right foot staggered behind the lead foot that was placed on the starting line. The subjects were instructed to lead with the right foot. Trials were repeated when false steps occurred. Sprint time was measured by an accelerometer, attached to a waist belt, integrated with an electronic timing gate system (Inform Sport Training Systems, Victoria, BC, Canada). Data collection was initiated upon movement of the subjects and stopped with the timing gate. The results were collected through telemetry to a computer. The best time of 2 trials, separated with a 2-minute rest period, was used for analysis while the average step length and step frequency were also recorded through telemetry. Jump performance was measured after a minimum of 48 hours of rest.
One practice session took place to familiarize the subjects with the procedures and to practice the jump techniques. All jumps and sprints occurred during a similar time of the day. The jumps were analyzed using the same accelerometer instrument (Figure 1), worn on the waist, used to measure the sprints. For the drop jumps, the subjects stepped off of a box (40 cm for the bilateral jumps and 20 cm for the unilateral jumps) and dropped to the floor without stepping down or jumping up. Upon landing, the subjects were instructed to minimize contact time before jumping for maximum height or distance. During the countermovement jumps, the subjects were instructed to jump for maximum height or distance with a quick reversal from the eccentric to the concentric phase. The subjects' hands were held on the hips on all jumps to analyze lower-body performance. During the unilateral jumps, the subjects were instructed to not use the swing leg by limiting hip flexion for the purpose of isolating the use of the stance leg to propel the body (Figure 2). Trials were repeated when hip flexion of the swing leg was observed to lead in front of the stance leg. The unilateral tests were performed on the right and left legs. Horizontal displacement was the only variable not measured with the accelerometer software. A tape measure was placed on the floor to measure horizontal displacement. The distance from the toe at take-off to the heel of the closest foot to the starting line was measured to the nearest centimeter.
All jumps were completed in 1 session after a 5-minute jog and light lower-body stretching. The following jump tests were measured in random order for analysis: bilateral countermovement vertical jump (BCV), bilateral countermovement horizontal jump (BCH), bilateral 40-cm drop vertical jump (BDV), bilateral 40-cm drop horizontal jump, unilateral countermovement vertical jump (UCV), unilateral countermovement horizontal jump (UCH), unilateral 20-cm drop vertical jump (UDV), and unilateral 20-cm drop horizontal jump (UDH). The subjects completed 2 trials for each test with 30 seconds of rest between trials and a 1-minute rest period between each test. To eliminate potential learning effects across trials (4), 3 practice trials took place. The trial with the best jump height or distance, reactive strength (RS), and flight time to concentric contact time ratio (FT/CCT) was recorded for analysis.
All variables analyzed in this study were not measured for each type of jump because of the limitation of the software program designed for the accelerometer instrument. For the horizontal countermovement jumps, jump distance was measured with the use of the tape measure placed on the floor with the inclusion of jump distance/standing height for analysis. During the vertical countermovement jumps, jump height and FT/CCT were analyzed. In addition to measuring jump height and FT/CCT during the vertical drop jumps, total ground contact time (eccentric and concentric time) was measured to calculate and analyze RS. Jump distance, jump distance/standing height, and RS were analyzed for the horizontal drop-jump tests. The FT/CCT and RS are indicators of the stretch-shorten cycle performance to produce optimum impulse under these jump conditions. Although the FT/CCT is produced under lower loading forces during the countermovement jumps, this measure is also an indicator of the subject's stretch-shorten cycle ability as the concentric phase was preceded with an immediate reversal of an eccentric contraction.
High reliability of unilateral, horizontal drop displacement (intraclass correlation coefficient [ICC] = 0.95) (29) and countermovement hop for distance (ICC = 0.92) (27) has previously been determined. Similar results (ICC > 0.9) are shown to occur for the kinematic variables measured during the unilateral, vertical drop-jump test (7) and countermovement jump (ICC > 0.85) (20). High reliability has also been shown for the bilateral, vertical countermovement jump (ICCs ranging from 0.87 to 0.94) (21) and drop jump (coefficient of variation = 6.2%) (1). The test-retest reliability for this study ranged from 0.74 to 0.9 for the kinematic variables.
The dependent variables in this study were the sprint performance variables: 10-m sprint time, 10-m step length, 10-m step frequency, 25-m sprint time, 25-m step length, and 25-m step frequency. The independent variables in this study were the various jump kinematic variables. Because all variables were scaled continuously, Pearson product-moment correlations were used to analyze the relationship between the jump kinematic variables and the sprint performance variables. Paired t-tests were performed to determine if significant differences existed between limbs for the variables analyzed. Because no significant differences were found, the right and left limb data were pooled to determine the correlation analysis (11). For the unilateral analysis, right, left, and pooled data were reported. Holm et al. (11) found stronger significant correlations (−0.44 < r < −0.65, P < 0.05) between 5-, 10-, and 15-m sprint time and horizontal jump distance when normalized with body height. Thus, this normalization procedure was followed in this study.
Variable means and SDs are given in Table 1. None of the bilateral jump kinematic variables were significantly correlated with either 10- or 25-m sprint time, step length, or step frequency. The correlations between the unilateral vertical jump kinematic variables and 10-m sprint performances are reported in Table 2. None of these vertical jump variables were significantly correlated with 10-m sprint time, step length, or step frequency.
The correlations between the unilateral vertical jump kinematic variables and 25-m sprint performances are reported in Table 3. Right-leg UDV FT/CCT ratio (r = 0.68, p = 0.01) was significantly correlated with 25-m step length. Right-leg UCV jump height (r = −0.71, p = 0.006) and FT/CCT ratio (r = −0.58, p = 0.04) were significantly correlated with 25-m sprint time. When right- and left-leg values were averaged, the pooled UCV jump height (r = −0.61, p = 0.01) was also significantly correlated with 25-m sprint time.
The correlations between the unilateral horizontal jump kinematic variables and 10-m sprint performances are reported in Table 4. Although several measures approached significance, none of the UCH and UDH right- and left-leg measures were significantly correlated with either 10-m sprint time, step length, or step frequency. When right- and left-leg values were averaged, the pooled UDH jump distance/height variable (r = −0.58, p = 0.01) was significantly correlated with 10-m sprint time.
The correlations between the unilateral horizontal jump kinematic variables and 25-m sprint performances are reported in Table 5. Although moderate correlations were found for RS, none of these horizontal jump variables were significantly correlated with 25-m sprint time, step length, or step frequency.
The data indicate that unilateral jump performance have a stronger relationship with sprint performance than bilateral jump performance. This relationship is likely because of the unilateral requirement during the stance phase of jumping and sprinting. Significant correlations were found between the unilateral jumps and sprint performance, whereas no significant results occurred for the bilateral tests. Similar to Holm et al. (11), the relationship between the UDH and sprint performance was stronger when the jump distance was analyzed relative to the subjects' height. Although moderate significant correlations have been found between bilateral jumps and sprint performance (5,15,32), our results are in agreement with the few studies that have included unilateral and bilateral jumps in the same study that showed stronger correlations with the unilateral jumps (17,23). In these studies, the unilateral jumps were horizontal, whereas the bilateral jumps were vertical. In this study, all of the jumps were performed unilateral and bilateral for direct comparison.
With the requirement to produce primarily horizontal motion during the horizontal jumps and sprinting, it is surprising that the only significant correlation found for the horizontal tests was between the UDH and the 10-m sprint time. These results are consistent with Holm et al. (11), who found stronger correlations between kinematic variables assessed during the UDH jumps and the shorter sprints (≤10 m) compared to the longer sprints (10-25 m). In comparison to the countermovement jump, higher loads and subsequent forces that occur during drop jumps are likely more similar to the high forces necessary to produce the leg drive during the acceleration phase of sprinting opposed to sprinting near top velocity.
The early acceleration has been described to be primarily (81% of the duration) a concentric propulsion task (19) differing from sprinting at top velocity, which is suggested to rely more on the stretch-shorten cycle (9). All of the jumps included in this study required a countermovement that involves a stretch-shorten cycle, which may explain, in part, the lack of relationship found between the jumps with 10-m sprint performance. Young et al. (33) found a strong relationship between concentric force during the squat jump and 2.5-m sprint time (r = −0.86) and force during jump squats with light loads (9-19 kg) that includes the stretch-shorten cycle (r = −0.77). Baker and Nance (2) reported similar significant results between concentric force and 10-m sprint time, but not for 40-m sprint time, and concluded that jumps relying on the stretch-shorten cycle may correlate better with 40-m sprint time. The inclusion of the horizontal and vertical squat jump in this study may have produced a stronger relationship with a 10-m sprint performance.
The unilateral vertical jump kinematic variables (jump height and FT/CCT) were significantly related to 25-m sprint time, whereas none of the horizontal jump variables were found to be significant at this distance. These data do not support our hypothesis that stronger correlations would be found in the horizontal jumps. High vertical forces at take-off have previously been determined to produce a negative interaction with sprint performance (12). Hunter et al. (12) concluded that high step lengths and step rates achieved by elite sprinters may possibly occur only with high horizontal and low vertical forces. Thus, it is unclear why stronger correlations were not found between the unilateral horizontal jump variables and 25-m sprint performance. A lack of training experience with horizontal jumps similar to the technique used during the tests may have had an attenuating affect on the correlations. In addition, sprinting short distances and landing from a vertical fall then transitioning to produce a horizontal jump in the drop jump present different loading conditions.
Differences in the technique used to perform the different jumps may in part explain differences in results across studies. In this study, the hands were placed on the hips with no help from the swing leg to propel the body during the horizontal jumps. Although similar significant correlations have occurred between the unilateral, horizontal jumps and sprint time with the use of the arms (23) and with the hands held on the hips (12,20), previous investigations (12,18,20,23) have not addressed the specific instructions provided to the subjects for the control of the swing leg. Holm et al. (11) provided a clear illustration of the technique, whereas Nesser et al. (23) described that the 5-step jump was performed similar to a triple jump. In these studies, hip flexion appeared to be allowed in the swing leg during extension of the stance leg to help propel the body. Meylan et al. (20) did not provide instructions for the swing leg. Previous research has determined that significantly greater hip flexion muscle recruitment occurs in the swing leg during horizontal jumps in comparison to vertical jumps to propel the body's center of mass (22). The subjects in this study were instructed to keep the swing leg from leading the stance leg through the ground contact phase. The data from previous research indicate that allowing hip flexion of the swing leg produces stronger correlations with sprinting compared to preventing hip flexion. Allowing hip flexion in the horizontal jumps also more closely simulates the movement patterns of sprinting.
In contrast to the horizontal data in this study, the results indicate that training to improve UCV jump height and FT/CCT may enhance 25-m sprint time in collegiate women soccer players. In addition, training with UDV jumps may improve step length. This speculation is supported by the significant correlation found between UDV FT/CCT and step length during the 25-m sprint possibly resulting from both variables requiring an ability to produce high forces with short contact times. With only 1 variable significantly related to step length, further data are needed to corroborate theses results. The FT/CCT and jump height found during the UCV were also significantly related to 25-m time. The FT/CCT and RS can be considered as indicators of the stretch-shorten cycle ability, as the UCV included a quick reversal from the eccentric to the concentric phase.
It is unclear as to why RS did not also show a significant relationship with sprint performance. Reactive strength may show a stronger relationship with sprinting longer distances than those used in this study because of the requirement to produce forces in less contact time (ca. 0.1 seconds) at peak running velocity compared to early acceleration (ca. 0.2 seconds) (30). Running 25 m may not provide enough time to sprint for a significant duration near top velocity, which may have affected the relationship between RS and sprint performance. Few studies were found in the review of the literature that analyzed the relationship between jump performance and sprint performance at longer sprint distances (100 m). A recent study (13) reported significant correlations between 100-m sprint time and max velocity and several types of vertical jumps while finding no significance in the horizontal jumps. However, a previous study (24) found significant correlations with maximum sprint velocity during the 100 m and several types of horizontal jumps. Horizontal jump performance may show a stronger relationship with maximum sprint velocity than sprint time during a 100-m sprint as several types of sprint characteristics (acceleration, peak velocity, and maintenance) occur during this distance. Further investigations are needed for comparison of results at this longer sprint distance.
Stronger correlations may have also been determined in this study with measurement of kinetic factors. Chamari et al. (5) and Maulder et al. (17) found significant correlations between force and power produced during the BCV and 20- to 30-m and 10-m sprint time, respectively, but not for jump height. As a result, Maulder et al. (17) suggested that force and power data may be more sensitive for expressing a relationship with sprint performance. In agreement with our results, Maulder et al. (17) did not find significant correlations between UCH distance and unilateral triple hop for distance and 10-m sprint time, which contrasted the results of their earlier study that did find a significant relationship the UCH and triple hop for distance (r = −0.74 to −0.86) with 20-m sprint time (18). Differences in subjects across studies were speculated to determine the differences revealed between these studies. Sportsmen with a wide range of sprint requirements participated in the study by Maulder and Cronin (18) while elite male sprinters completed the more recent study by Maulder et al. (17). In contrast to Maulder and Cronin (18), women soccer players participated in this study, who also require a wide range of running abilities, yet significant correlations were not found between UCH and UDH distance and 25-m sprint performance.
Few studies have analyzed the relationship between jumping and sprint performance in highly competitive female athletes. Liebermann and Katz (16) found a significant correlation (r = −0.88) between mean peak power during the BCV and 20-m sprint time in combined group of male and female subjects with a range of sport participation from amateur to highly competitive. The combination of using men and women and the wide range of sport participation may have artificially increased the correlations between jumping and sprint time. Men and women physical education students were analyzed in separate data sets in a study by Meylan et al. (20), who found a significant relationship between UCH distance (r = −0.65) and UCV jump height (r = −0.61) and 10-m sprint time for the men. For the women in this previous study, UCV jump height (−0.44) demonstrated the highest relationship with 10-m sprint time while the UCH distance was low (r = −0.34) yet significant. These data are in partial agreement with our study that consistently found higher correlations between the unilateral, vertical jump tests and sprint performance. In contrast, we found significant correlations between the vertical jump tests and 25-m sprint time but not during the 10-m sprint. With vertical jump kinematics revealing more consistent significant results, our findings are also in partial agreement with a prior study of nationally ranked female sprinters by Hennessy and Kilty (9). Significant correlations were determined between BCV height and BDV RS and 30- and 100-m sprint times, but no significant relationship was found between the 5-step UCH distance and sprint performance (9). Comparison of these results with our current study is limited because this previous study did not compare unilateral and bilateral tests for each type of jump. The subjects' gender and competitive level of the athlete appear to affect the relationship between the variables analyzed between jump and sprint performance, but further studies are needed to better understand the relationships and mechanisms that determine these differences.
Although not investigated in this study, muscle stiffness, shown to differ among athletic populations and men vs. women (3,10), has been reported to be a primary determinant of jumping and sprint performance (8,14). Kuitunen et al. (14) revealed that muscle stiffness increased as running velocity increased; thus, muscle stiffness may be most similar between the unilateral vertical jumps and the 25-m sprinting test for the subjects in this study in comparison to the other tests included. We also postulate that muscle stiffness requirements are likely different between vertical and horizontal jump tests. Although the eccentric phase occurs under similar gravitational loading conditions for the horizontal and vertical jump tests, the differences in the direction of movement opposing gravity between the jump tests during the propulsion phase may have produced differences in muscle stiffness levels. Meylan et al. (20) reported <50% of shared variance between the UCV and UCH tests for men and women while concluding that the jumps were independent of each other and measure different abilities.
Single repetition trials were completed in this study. Higher leg-spring stiffness has been shown during successive repetitions during the UDV tests compared to a single UDV repetition (8). Muscle stiffness during consecutive vertical hopping has also shown to be related to 40-m sprint velocity but not early acceleration (6). Nesser et al. (23) found that the 5-step unilateral hop test for distance was the best predictor (−0.81) of 40-m sprint time in male subjects active in various sports while BCV power did not significantly contribute to the prediction of sprint time. These studies provide some support that consecutive jumps may produce a stronger relationship with running near top velocity than the single repetitions used in this study.
Several limitations of this study yet to be noted should be considered. The accelerometer software did not measure ground time during the countermovement horizontal jumps; thus, the analysis was limited to jump distance. Split times were not measured, which limits the sprint test as a measure of average velocity. Although using 10 and 25 m likely measures different sprint abilities, using a longer sprint displacement and split times may better differentiate between qualities of sprint performance. Another limitation of this study is the relatively small sample size. Because the purpose of the study was to measure the kinematic variables influencing sprint speed, step frequency, and step length in well-trained division I collegiate soccer athletes during their competitive season, untrained subjects were excluded from the study. Because of the effect that training state might have on the relationships among the variables, the possible extraneous variable of training state was controlled by recruiting only well-trained soccer athletes who compete at a high level of performance. This constraint limited the size of the sample, and the comparisons being made in this study warrant replication with larger samples in future research.
The data indicate that unilateral jump tasks demonstrate a stronger relationship with sprint performance than bilateral jumps in female soccer players. Based on these findings, the strength and conditioning specialist should consider including unilateral jumps into the training program for female soccer players to improve sprint performance. According to our results, both unilateral drop and countermovement jumps are appropriate to include in jump training programs to improve sprint performance; however, further training studies are needed to confirm this speculation. Although performing the unilateral jumps during training to improve sprinting, allowing hip flexion may be most effective. Single repetition jumps were performed with moderate correlations determined; therefore, consecutive horizontal jumps may show a stronger relationship with sprint performance and may be more effective to include in a sprint-training program.
We would like to thank the Texas State University soccer head coach, Kat Conner, and assistant coach, Megan Ramey, for their cooperation with this study. We would also like to thank the soccer players for their willingness to participate and provide maximum effort during the study.
1. Arteaga, R, Dorado, C, Chavarren, J, and Calbet, J. Reliability of jumping performance in active men and women under different stretch loading conditions. J Sports Med Phys Fitness
40: 26-30, 2000.
2. Baker, D and Nance, S. The relation between running speed and measures of strength and power in professional rugby players. J Strength Cond Res
13: 230-235, 1999.
3. Blackburn, J, Riemann, B, Padua, B, and Guskiewicz, K. Sex comparison of extensibility, passive, and active stiffness of the knee flexors. Clin Biomech
19: 36-43, 2004.
4. Booher, L, Hench, K, Worrell, T, and Stikeleather, J. Reliability of three single-leg hop tests. J Sport Rehab
2: 165-170, 1993.
5. Chamari, K, Hachana, Y, Ahmed, Y, Galy, O, Sghaier, F, Chatard, J, Hue, O, and Wisloff, U. Field and Laboratory testing in young elite soccer players. Br J Sports Med
38: 191-196, 2004.
6. Chelly, S and Denis, C. Leg power and hopping stiffness: Relationship with sprint running performance. Med Sci Sports Exerc
33: 326-333, 2001.
7. Flanagan, E, Ebben, W, and Jensen, R. Reliability of the reactive strength index and time to stabilization during depth jumps. J Strength Cond Res
22: 1677-1682, 2008.
8. Flanagan, E and Harrison, A. Muscle dynamics differences between legs in healthy adults. J Strength Cond Res
21: 67-72, 2007.
9. Hennessy, L and Kilty, J. Relationship of the stretch-shortening cycle to sprint performance in trained female athletes. J Strength Cond Res
15: 326-331, 2001.
10. Hobara, H, Kimura, K, Omuro, K, Gomi, K, Muraoka, T, Iso, S, and Kanosue, K. Determinants of difference in leg stiffness between endurance- and power-trained athletes. J Biomech
41: 506-514, 2008.
11. Holm, D, Stalbom, M, Keogh, J, and Cronin, J. Relationship between the kinetics and kinematics of a unilateral horizontal drop jump to sprint performance. J Strength Cond Res
12. Hunter, J, Marshall, R, and McNair, P. Interaction of step length and step rate during sprint running. Med Sci Sports Exerc
36: 261-271, 2004.
13. Kale, M, Asci, A, Bayrak, C, and Acikada, C. Relationships among jumping performances and sprint parameters during maximum speed phase in sprinters. J Strength Cond Res
23: 2272-2279, 2009.
14. Kuitunen, S, Komi, P, and Kryolainen, H. Knee and ankle joint stiffness in sprint running. Med Sci Sports Exerc
34: 166-173, 2002.
15. Kukolj, M, Ropret, R, Ugarkovic, D, and Jaric, S. Anthropometric, strength, and power predictors of sprinting performance J Sports Med Phys Fitness
39: 120-122, 1999.
16. Liebermann, D and Katz, L. On the assessment of lower-limb muscular power capability. Isokin Exerc Sci
11: 87-94, 2003.
17. Maulder, P, Bradshaw, E, and Keogh, J. Jump kinetic determinants of sprint acceleration performance from starting blocks in male sprinters. J Sports Sci Med
5: 359-366, 2006.
18. Maulder, P and Cronin, J. Horizontal and vertical jump assessment: Reliability, symmetry, discriminative and predictive ability. Phys Ther Sport
6: 74-82, 2005.
19. Mero, A. Force-time characteristics and running velocity of male sprinters during the acceleration phase of sprinting. Res Q Exerc Sport
59: 94-98, 1988.
20. Meylan, C, McMaster, T, Cronin, J, Mohammad, N, Rogers, C, and DeKlerk, M. Single-leg lateral, horizontal, and vertical jump assessment: reliability, interrelationships, and ability to predict sprint and change-of-direction performance. J Strength Cond Res
21. Moir, G, Shastri, P, and Connaboy, C. Intersession reliability of vertical jump height in women and men. J Strength Cond Res
22: 1779-1784, 2008.
22. Nagona, A, Komura, T, and Fukashiro, S. Optimal coordination of maximal-effort horizontal and vertical jump motions-A computer simulation study. Biomed Eng Online
23. Nesser, T, Latin, R, Berg, K, and Prentice, E. Physiological determinants of 40-meter sprint performance in young male athletes. J Strength Cond Res
10: 263-267, 1996.
24. Osinski, W. The study of running speed in the cause-effect system of path analysis. J Sports Med Phys Fitness
28: 280-286, 1988.
25. Rimmer, E and Sleivert, G. Effects of a plyometrics intervention program on sprint performance. J Strength Cond Res
14: 295-301, 2000.
26. Ronnestad, B, Kvamme, N, Stunde, A, and Raastad, T. Short-term effects of strength and plyometric training on sprint and jump performance in professional soccer players. J Strength Cond Res
22: 773-780, 2008.
27. Ross, M, Langford, B, and Whelan, P. Test-retest reliability of 4 single-leg horizontal hop tests. J Strength Cond Res
16: 617-622, 2002.
28. Spurrs, R, Murphy, A, and Watsford, M. The effect of plyometric training on distance running performance. Eur J Appl Physiol
89: 1-7, 2003.
29. Stalbom, M, Holm, D, Cronin, J, and Keogh, J. Reliability of kinematics and kinetics associated with horizontal single leg drop jump assessment. A brief report. J Sports Sci Med
6: 261-264, 2007.
30. Viitasalo, J, Luhtanen, P, Mononen, H, Norvapalo, K, Paavolainen, L, and Salonen, M. Photocell contact mat: A new instrument to measure contact and flight times in running. J Appl Biomech
13: 254-266, 1997.
31. Wilson, J and Flanagan, E. The role of elastic energy in activities with high force and power requirements: A brief review. J Strength Cond Res
22: 1705-1715, 2008.
32. Young, W, Hawken, M, and McDonald, L. Relationship between speed, agility, and strength qualities in Australian Rules football. Strength Cond Coach
4: 3-6, 1996.
33. Young, W, McClean, B, and Ardagna, J. Relationship between strength qualities and sprinting performance. J Sports Med Phys Fitness
35: 13-19, 1995.