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.
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Keywords:© 2010 National Strength and Conditioning Association
reactive strength; vertical jump; horizontal jump; unilateral jump; bilateral jump