Journal of Athletic EnhancementISSN: 2324-9080

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Research Article, J Athl Enhancement Vol: 4 Issue: 3

Effect of a Single Jump Practice on Vertical Jump Performance

Yoshimoto T1, Takai Y1*, Ishii Y2, Kanehisa H1 and Yamamoto M1
1National Institute of Fitness and Sports in Kanoya, Japan
2Japan Institute of Sports Sciences, Japan
Corresponding author : Yohei Takai, PhD
National Institute of Fitness and Sports in Kanoya, Shiromizu-cho, Kanoya, Kagoshima, 891-2393, Japan
Tel/Fax: +81-994464992
E-mail: [email protected]
Received: November 20, 2014 Accepted: June 05, 2015Published: June 11, 2015
Citation: Yoshimoto T, Takai Y, Ishii Y, Kanehisa H, Yamamoto M (2015) Effect of a Single Jump Practice on Vertical Jump Performance. J Athl Enhancement 4:3. doi:10.4172/2324-9080.1000196

Abstract

Effect of a Single Jump Practice on Vertical Jump Performance

Objective: This study aimed to elucidate the effect of a single jump practice session on vertical jump height. Thirty-two physical educational students aged from 19 to 27 years participated in this study. Methods: This study consisted of a randomized, controlled, and longitudinal design. The participants were divided into two groups; the intervention group (EX, n=16) and the control group (CG, n=16). The EX group performed five vertical jumps from a platform located at their knee height. The CG group was instructed to jump five times as high as possible without a platform. Before and after the jump practice, we determined vertical jump height, vertical ground reaction ground force, and the joint angles of trunk and lower extremity. Results: After the practice sessions, vertical jump height was significantly increased in EX, but was significantly decreased in CG. In EX, the change in vertical jump height was related to changes in the hip joint and trunk inclination angles. In CG, no change was found in the kinematic data. Conclusions: A single jump practice using a platform at one’s knee high transiently improves vertical jump height, and the change is associated with changes in the kinematics of the hip joint and trunk inclination. This implies that the coach or practitioner needs to pay attention to a protocol for familiarization trials and warm up when the vertical jump test is used to assess muscular power.

Keywords: Trunk; Lower extremity; Joint angle; Ground reaction force

Keywords

Trunk; Lower extremity; Joint angle; Ground reaction force

Introduction

Assessment of vertical jump capability provides important insights into whole body power output in sports and health sciences [1,2]. The mechanical energy for maximal jumps comes mostly from the thigh and hip musculature [3-8]. Fukashiro and Komi [4] showed that hip joint mechanical work was higher than that in the knee and ankle during a countermovement jump with the hands held on the hips. In contrast, Luhtanen et al. [9] indicated that knee extension movement during vertical jumping contributed to maximal take-off velocity during the vertical jump. Hubley et al. [3] found that the knee, with 28% and 23% contributed by the hip and ankle, respectively, did 49% of the total positive work produced during the jump. Vanrenterghem et al. [10] also demonstrated that decreased forward inclination of the trunk resulted in attenuation of vertical jump height, because of hip joint torque and power decrease during countermovement. These finding indicate that the strength capability of lower extremity is one of the determinants for jump capability.
On the other hand, changes in kinetics and kinematics of vertical jump would result in enhancement of the jump performance. In fact, Salles et al. [11] reported that the effect of countermovement on vertical jump height was higher at 90º of knee joint angle compared to those at 50° and 70°. They also demonstrated that hip and ankle joint torques during the vertical jump were higher at 90° of knee joint angle than at 50° and 70°. Van Soest et al. [12] have suggested that jump height was higher in the deeper position than in the preferred position, when jumps were optimally activated from deep squats. Furthermore, Domire at al. [13] examined the difference in vertical jump height between two different jump strategies (jumping from the preferred depth vs. one from the deeper depth). As the result, jump height was unchanged, but kinematic data on the hip and knee joint angles and center of mass height were differed between the two jumps. As a potential factor of no change in jump height, they speculate that jumping from a deep squat is not often practiced, so the participants presumably were not as well coordinated in the deep squats as they were from their preferred depth. In our previous study, a single jump practice from platform set at subject’s knee height enhances vertical jump height in youth [14]. Based on these findings, it is assumed that jumping practice using a platform at one’s knee’s height makes the depth of a preliminary downward movement to be deeper. To the best of our knowledge, it is unknown whether a jump practice session improves the jump movement pattern and performance.
Hirayama et al. [15] have shown that even a single jump practice can improve performance in a countermovement jump using only the ankle joint. Considering this finding, it may be assumed that a single jump practice would transiently increase jump height with a modulation of their movement patterns, which contributes to the performance improvement. The purpose of this study was to examine whether the single jump practice improves vertical jump height with changing jump movement pattern. The hypothesis of this study was set that a single jump practice would change the hip and knee joint angles to be more flexed and improve the vertical jump height.

Materials and Methods

Experimental approach to the problem
Previous studies have indicated that the differences in kinetic and kinematic of vertical jump would result in that of the jump performance. To the best of our knowledge, it remains unclear whether kinetics and kinematics changes in vertical jump induce the improvement of jump performance. In our previous study, a single jump practice from platform set at subject’s knee height enhances vertical jump height in youth [14]. However, it is unclear whether the improvement of jump height results from the change in kinetics and kinematics data or from postactivation potentiation effect in our previous study. Therefore, the kinetics and kinematics data before and after the single jump practice session were determined. Furthermore, to distinguish practice-induced change in jump performance from augmentation due to the postactivation potentiation effect, the subjects were divided into two groups: the intervention group (EX) which squatted onto the platform, and then maximally jumped immediately when their hips were touched on the platform vs. the control group (CG) which performed countermovement jumps as high as possible from their preferred depth.
Participants
Thirty-two male physical educational students participated in this study. The subjects were divided into two groups; the intervention group (EX, n=16, 175.0 ± 4.1 cm, 68.1 ± 5.4 kg, 20.8 ± 1.2 years, means ± SDs) and the control group (CG, n=16, 172.5 ± 4.8 cm, 65.6 ± 7.1 kg, 22.0 ± 2.2 years). The mean values of age, height and body mass were not significantly different between the two groups. The subjects were either mildly and active and regularly participated in a specific exercise program (e.g. track and field, soccer and strength training). Data collection was conducted in season for each subject from 2011 to 2013. They were free from cardiovascular, metabolic, immunologic disorders and orthopedic abnormality, and did not use any medications that affect muscle function. This study was approved by the ethical committee of the National Institute of Fitness and Sports in Kanoya and was consistent with their requirements for human experimentation. Prior to the experiment, all subjects were informed of the experimental procedures of this study and possible risks of the measurements beforehand. Written informed consent was obtained from each subject. The purpose and hypothesis of the study were not explained to the subjects until termination of measurements, to exclude any potential bias that might affect the results.
Experimental protocol
This study consisted of a randomized, controlled, and longitudinal design. The experimental protocol of this study is presented in Figure 1A. Before the experiment, each subject completed standardized warm-up with static stretching (5 min) and jogging (subjective intensity: 30-50% of maximal effort) on a non-motorized treadmill for 5 min. Then, the subjects vertically jumped three times with their hands held on their hips with maximal effort before a jump practice, with a rest interval of 5 min. The depth of squat was left to the subject’s preference. This procedure was repeated three times (the first, second, and third measurement trials; M1, M2, and M3). A single vertical jump practice was performed before M2 and M3. As the jump practice, the EX performed five vertical jumps from a platform set at subject’s knee height, with a 30 s rest (Figure 1B). The height of the platform was adjusted for each participant. The participants squatted onto the platform, and then maximally jumped immediately when their hips were touched the platform. In contrast, the CG was instructed to jump five times as high as possible without the platform, with an interval of 30 s (Figure 1B). In each trial, feedback on jump height was not given to the subjects after a jump. Subjects were asked to land from a jump in a fully extended position with full extension at the hips, knees, and ankles. In the testing trials, vertical ground reaction force and kinematic data were recorded using a force plate and a three dimension motion capture system, respectively.
Figure 1a: Experimental design.
Figure 1b: Photography of each single jump practice in the intervention and control groups.
Measurements
Ground reaction force: Vertical ground reaction force was recorded using a force plate (Z15907, Kistler, Japan). The signals of the reaction force were amplified and A/D converted (PowerLab/16sp, ADInstruments, Australia) at sampling rate of 1 kHz and transmitted to a computer. The force measured at the onset of each jump was set as the baseline (offset to zero) and integrated until the force dropped to the baseline to determine the impulse. The vertical ground reaction force was analyzed from a maximal knee-flexed position to take-off. The peak values were calculated, and were normalized to body mass. Vertical jump height was calculated as follows [16]; jump height (cm) = g × t2 × 8-1, where g is acceleration due to gravity (9.81 m/s2) and t is time of flight during the jump (s). The t taken from takeoff to ground contact was measured by the force platform. In each measurement trial, the highest value among three vertical jumps for each participant was adopted and used for later analysis.
Kinematics in trunk and lower extremity: Kinematic data were collected by a three-dimension motion capture system (Mac3D system, Motion Analysis, USA). Joint angles of the trunk and lower extremity were calculated from the obtained data. Twelve cameras operating at 250 frames/s were positioned surround the force plate. Reflective markers were attached to the acrominon, the greater trochanter, the border between femur and tibia, lateral malleolus, and fifth metatarsal. Each joint angle was analyzed from coordinate data in the sagittal plane (Figure 1C). The representative values of the ankle joint, thigh, trunk and lower leg inclination angles were calculated from 90° minus the obtained angles. The representative values of hip and knee joint angles were calculated from 180° minus the obtained angles
Figure 1c: Definition of trunk and lower extremity joint angle in the sagital plane.
Statistical analysis
Descriptive data are presented as the means ± SDs. The normality of the measured variables was tested by Kolmogorov-Smirnov test. If the normal distribution was satisfied, non-parametric analysis was performed for the independent variable. An unpaired t-test was used to test a significant difference between both groups. For vertical jump height, a two-way analysis of variance (ANOVA) with repeatedmeasures (2 groups, EX vs. CG × three time points of the measurement trials, M1 vs. M2 vs. M3) was used to test the main effects of group and time and their interaction. When the significant interaction between group and measurement trial was found, a simple main effect test with a Bonferroni post hoc test was used to test a significant change in vertical jump through the intervention in each group. To determine the changes in kinematic and kinetic data during the jump practice, a one-way ANOVA with repeated-measures was performed to test the significance of difference in mean values between M1 and the 2 jump practices in each group. In case of the non-parametric analysis, Mann-Whitney U’s test was used to compare EX with CG at baseline, and a Friedman’s test was conducted to test a significant difference among the three measurement trials, and a Wilcoxon signed-rank test with Bonferroni correction was used to compare M1 with M2 and M3 in each group. Pearson’s correlation coefficient (r) was calculated to assess the relationship between change in jump height and that in kinematic and kinetic data. Coefficient of variance (CV, %) in jump height was calculated from the following equation; SD/Mean × 100 in each measurement trial. Effect size was classified as trivial (r<0.1, η2<0.01), small (r=0.1-0.3, η2=0.01-0.06), moderate (r=0.3-0.5, η2=0.06-0.14), and large (r>0.5, η2>0.14) [17]. Confidence interval (CI) was set at 95%. Statistical significance was set at p<0.05. All data analyses were conducted using a statistical software package (IBM SPSS Statistics 20, IBM Japan).

Results

Comparison between EX and CG in all measured variables at M1 (Table 1)
There was no significant difference between the two groups in vertical jump height, joint angle (except for thigh inclination angle), and ground reaction force at baseline. For the thigh inclination angular velocity from stand to maximal flexed position at the knee, and the peak angular velocities of thigh and leg inclination from maximal flexed position at the knee to take-off were faster in CG than in EX.
Table 1: Descriptive data of the kinematic and kinetic data at baseline.
Change in vertical jump height through the practice (Figure 2)
The two-way ANOVA revealed a significant interaction between group and time (F=17.414, η2=0.02, p<0.05). In the EX, the jump practices significantly increased vertical jump height at M2 (40.9 ± 2.9 cm (39.2-42.6, CIs)) or M3 (41.4 ± 3.1 cm (39.6-43.3)) compared to M1 (39.9 ± 2.9 cm (38.2-41.7)) by 3.7%. In the CG, the vertical jump height was significantly decreased from M1 (40.7 ± 3.9 cm (38.9- 42.5)) to M3 (39.7 ± 4.0 cm (37.8-41.5)) by -2.5%. The CVs of jump height were 1.2 ± 0.7% in M1, 2.1 ± 1.4% in M2, 1.6 ± 0.9% in M3 for EX, and 2.3 ± 1.9%, 2.2 ± 1.4%, and 2.0 ± 1.0% for CG, respectively.
Figure 2: Change in vertical jump height through intervention for the intervention (•) and control (ο) groups.
Changes in joint angle through the practice (Figure 3a-b)
None of the joint angles in the standing position differed among the test trials. In the EX, the ANOVA revealed the significant main effects in hip joint (F=5.4, η2=0.02, p<0.05) and trunk inclination (F=4.5, η2=0.01, p<0.05) angles with small effect size. As the result of post hoc test, hip joint and trunk inclination angles at maximal flexed position at knee tended to be significantly greater at M2 and M3 compared to M1, but the level of significance were not reached (p=0.055 for hip joint angle, and p=0.092 for trunk inclination angle) (Table 2). In the CG, The ANOVA revealed the significant main effects in hip joint (F=8.4, η2<0.01, p<0.05) and trunk inclination (F=5.6, η2<0.01, p<0.05) angles in the EX with trivial effect size. As the result of post hoc test, both angles at M2 (p<0.05 for hip joint angle, and p<0.05 for trunk inclination angle) and M3 (p<0.05 for hip joint angle) was significantly increased compared to M1 (Table 3). Pearson’s correlation coefficients between change in vertical jump height and changes in the measured variables are summarized in Table 4. In the EX, the change in vertical jump height was positively correlated to those in hip joint (r=0.63 from M1 to M2, r=0.487 from M1 to M3, p<0.05) and trunk inclination (r=0.57 from M1 to M2, r=0.67 from M1 to M3, p<0.05) angles with large effect size. In the CG, the change in vertical jump height was negatively correlated to those in trunk inclination angle (r=-0.75 from M1 to M3, p<0.05).
Figure 3a: Time courses of the kinematic data in the trunk and lower extremity in the intervention (A) and control .
Figure 3b: Time courses of the kinematic data in the trunk and lower extremity in the intervention control (B) groups.
Table 2: Descriptive data of the kinematic and kinetic data in the intervention group (n=16).
Table 3: Descriptive data of the kinematic and kinetic data in the control group (n=16).
Table 4: Correlation coefficients between changes in vertical jump height and the measured variables.
Changes in angular velocity through the intervention
In the EX, the ANOVA revealed significant main effects in trunk inclination (F=6.8, η2<0.01, p<0.05) and lower leg inclination (F=3.7, η2<0.01, p<0.05) angular velocity from maximal flexed position at knee to takeoff with trivial effect size. As the result of post hoc test, the peak angular velocity of the trunk inclination from maximal flexed position at the knee to takeoff was faster in M2 and M3 compared to M1 (p<0.05, respectively). Peak hip angular velocity was significantly increased from M1 to M3. In the CG, the ANOVA did not revealed any significant main effects in the measured variables. For the EX, the change in vertical jump height through the intervention was positively related to those in peak hip (r=0.61, p<0.05) and thigh inclination (r=0.66, p<0.05) angular velocities (Table 4) with large effect size. In the CG, the corresponding change was significantly correlated to that in trunk inclination angular velocity during the vertical jump (r=0.51-0.61, p<0.05) with large effect size (Table 4).
Changes in kinetics data during jumping through the intervention
In the EX, the ANOVA revealed significant main effects in impulse (F=5.2, η2=0.01, p<0.05) and it relative to body mass (F=5.0, η2=0.01, p<0.05) with small effect size. As the result of post hoc test, the absolute and relative values of impulse tended to decrease from M1 to M3, but the levels of significance were not reached (p=0.073- 0.086). In the CG, the ANOVA revealed significant main effects in ground reaction force (F=4.9, η2<0.01, p<0.05) and it relative to body mass (F=4.8, η2<0.01, p<0.05) with trivial effect size. As the result of post hoc test, the absolute and relative values of ground reaction force tended to decrease from M1 to M3, but the levels of significance were not reached (p=0.057-0.093). In both groups, there was no significant association between the changes in the vertical jump height and the kinetic data.
Change in joint angles of trunk and lower extremity during the jump practice session (Figure 4)
In the EX, the ANOVA revealed significant main effects in hip joint (F=9.9, η2=0.08, p<0.05) with large effect size, ankle joint (F=5.4, η2<0.01, p<0.05), thigh inclination (F=9.2, η2<0.01, p<0.05), and lower leg inclination (F=6.1, η2<0.01, p<0.05) angles with trivial effect size. As the result of post hoc test, hip joint (p<0.05) and thigh inclination angles (p<0.05) during the jump practice significantly increased compared to M1. Lower leg inclination angle during the jump practice significantly decreased from M1 to 2nd practice session (p<0.05). In the CG, the ANOVA revealed significant main effects in hip joint (F=9.9, η2<0.01, p<0.05), and thigh inclination (F=3.9, η2<0.01, p<0.05) angles. As the result of post hoc test, there was no significant difference between M1 and each jump practice session.
Figure 4: Changes in the kinematic data of trunk and lower extremity during the jump practice session in the intervention (A) and control (B) groups compared to those before intervention.

Discussion

As hypothesized at the start of this study, a single jump practice using a platform set at subject’s knee height transiently improved vertical jump height by changing hip joint and trunk inclination angles. The hip joint, thigh and lower leg inclination angles during jump practice session in the EX significantly increased, but the corresponding changes were not found in the CG (Figure 4). This implies that the current jump practice may transiently produces kinematic change in vertical jump. In addition, the change in vertical jump height from M1 to M3 was associated with those in kinematics and kinetics in the EX, whereas not in the CG. Taken together, it is possible that the observed enhancement in jump performance for the EX is due to the changes in the kinematics of the trunk and lower extremity during the vertical jump.
In the EX, the jump height increased through the jump practice session by 3.7%, but, in the CG, decreased by -2.5%. The CVs in vertical jump height were 1.2-2.3% in the measurement trials, indicating that the enhancement of jump performance in the EX can be due to the jump practice session.
In the EX, the hip joint and trunk inclination angles during the vertical jump showed more flexion after the single jump practice session, although the level of significance did not reached, although the corresponding angles significantly increased during the jump practice session (Figure 4A). It might be assumed that the practice period being too short to change the gross jump movement pattern. On the other hand, the current results show that the changes in the kinematic data were correlated to the magnitude of jump height. This might imply that transient change in kinematic induced by the jump practice session vary with each individual.
Vanrenterghem et al. [10] demonstrated that decreased forward inclination of the trunk resulted in attenuation of vertical jump height, because of hip joint torque and power decrease during countermovement. This indicates that change of hip joint may affect that in the torque and power generation. In the current results, the hip joint and trunk inclination angles during the vertical jump tended to make more flexed after the single jump practice session. Furthermore, the change in vertical jump is positively related to that in the corresponding joint angles. Considering these findings, the observed enhancement of jump height might be affected by change in torque and power generation of hip joint.
The vertical ground reaction force during vertical jump was 19.0 N/kg in the EX, being similar to the value at 90° reported by Salles et al. [11]. Salles et al. [11] demonstrated that a countermovement jump with knees flexed at 90° (19.6 N/kg) attenuated the peak ground reaction force relative to body mass compared to flexion at 50° and 70° (25-34 N/kg). However, the corresponding findings were not found in this study. This might be due to the magnitude of changes in the range of motion. In the current study, the mean value of change in knee joint angle was approximately 4°, being considerably smaller than those set by Salles et al. [11].
Interestingly, the vertical jump height for the CG decreased after the jump practice in which the participants were asked to repeat jumps as high as possible with no change in the joint kinematics, whereas that for the EX increased after the current jump practice with changing the hip joint and trunk inclination angles. In the earlier study, jumping movement pattern do not change from childhood to adulthood [18]. However, our findings indicate that a single jump practice with a platform set at one’s knee height transiently changes jumping movement pattern even in adults.
The observed enhancement of jump performance can be due to a postactivation potentiation effect. In fact, some studies have shown that the enhancement of jump performance following the plyometric and resistance exercises may be due to a postactivation potentiation effect [19,20]. To confirm it, the CG was asked to perform countermovement jump with their preferred modes in this study. The current result showed that the vertical jump significantly decreased through the intervention in the CG. This indicates that the improvement of jump height in this study may not be due to a postactivation potentiation effect.
Considering the current findings with our previous study, which the current jump practice is applied to boys from pre-, and postpubescence [14], the modality can be applied to the individuals from childhood to adulthood. However, whether the enhancement of jump performance can be applied to other groups (e.g. higher fitness level or females) is remained. Furthermore, the enhancement of jump performance in this study was transient effect. So, it is unclear that the short- and long-term practice is effective for more improvement of jump performance.

Practical Applications

The single jump practice with a platform set at one’s knee height transiently improved vertical jump height, and the improvement is due to the changes in trunk and hip joint movement. The current jump practice can be convenient modality in the athletic field because of less spatial and physical restrictions (e.g. training machine). On the other hand, the current findings imply that the coach or practitioner needs to pay attention to a protocol for familiarization trials and warm up when the vertical jump test is used to assess muscular power.

Conclusions

Jump practice using a platform set at subject’s knee height transiently improves vertical jump height, and produces changes in the kinematics of the trunk and lower extremity, which contribute to increased jump height. The current single jump practice can be recommended as a measure to change in jump movement pattern and to improve jump height for young individuals.

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