Vertical jumping has been described as a complex human movement that requires a high degree of motor coordination between upper- and lower-body segments (23). The maximum jump height achieved by an individual, which is an indicator of leg muscular power, can provide key information about their functional capacity and performance in many sports (6). In fact, vertical jumping is considered an essential motor skill in a range of team sports, including soccer (37), basketball (43), volleyball (33), and handball (20).
Many protocols are used to assess vertical jump ability. Specifically, soccer and basketball studies have used standardized jump tests from a standing position using a 2-legged take-off (i.e., countermovement jump [CMJ], drop jump [DJ], squat jump [SJ], and Abalakov jump [AJ] tests (17,27,43)). However, in basketball and soccer, the characteristics of vertical jumping may be influenced by an array of different game-related factors that include the trajectory of the ball, the skill level of the players, body contact with surrounding players, or the type of action performed (offensive or defensive). These factors make each jump a relatively different task. Thus, several studies (11,28) have called into question the validity of bilateral vertical jump tests in measuring the functional jumping capacity of soccer or basketball players and advocated for performing more sport-specific jump tests to assess strength and power characteristics. However, there is a lack of empirical knowledge relating to the reliability of sport-specific jump tests.
Reliability refers to the reproducibility of values in a test when a subject performs the test repeatedly, and it provides an indication of the degree of precision associated with a particular measure (18). A test with poor reliability is unsuitable for tracking changes in performance between trials, and it lacks precision for the assessment of performance in a single trial (18). The reliability of standardized bilateral vertical jump tests (CMJ, SJ, DJ, and AJ) has been widely analyzed in previous studies (1,3,9,23,24,26,34), which have reported small within-individual variation (coefficient of variation [CV]) and a high intraclass correlation coefficient (ICC). In contrast, to the best of our knowledge, only 2 previous studies (28,32) have analyzed the reliability of a sport-specific jump test. Furthermore, most of the aforementioned studies analyzing the reliability of different vertical jumps were conducted with adult and nonathlete participants (23–26), and few were performed using professional athletes as test individuals (9,28,32). In addition, it has been found that the reliability of these jumps depends on the age and skill of the group evaluated. Therefore, whether the reliability of different vertical jump tests depends on the age of the players or the sport practiced remains unexplored.
Several authors have indicated that vertical jump performance may be highly relevant in assessing performance parameters that are important in a range of sports. In fact, vertical jump performance is related to maximal strength, sprint ability, and change of direction (8,24,41). However, there is little information about whether different jump tests assess independent qualities or are strongly interrelated, or whether sport-specific jump tests show a stronger relationship with maximal strength and sprint ability than traditional vertical jump tests. Therefore, in line with the insights previously mentioned, the main aim of this study was to analyze the reliability and interrelationship of 4 different vertical jump tests (2 standing jump tests and 2 sport-specific jump tests) in soccer and basketball players in different age categories (Under-15, Under-18, and Adults). A secondary aim was to analyze the relationship between the different jump tests and the performance variables of maximal strength and sprint ability.
Experimental Approach to the Problem
This study was designed to assess the absolute and relative reliability and the interrelationship of 4 vertical jump tests: 2 standardized jumps using a 2-legged take-off (CMJ and AJ) and 2 specific-sport jumps with a previous run-up phase before the jump on either a 2-legged take-off jump (2-LEGS) or a 1-legged take-off (1-LEG). Another purpose of this study was to analyze the relationship between the different jump tests and straight sprint and maximal dynamic strength. To address this, players of different team sports (soccer and basketball) in 3 different age categories (U-15, U-18, and Adults) were tested using a battery of tests performed in the following order: (a) 20-m all-out running sprint; (b) CMJ; (c) AJ; (d) 2-LEGS; (e) 1-LEG; and (f) a progressive isoinertial loading test in full squat (FS) exercise. The testing session was conducted after the end of the season (off-season) when subjects were not involved in competitive activities. During the week preceding this study, 2 preliminary familiarization sessions were undertaken with the purpose of emphasizing the proper execution technique for FS and jump exercises.
One hundred eighty-six male soccer (n = 127) and basketball (n = 59) players in 3 different age categories (Under-15, Under-18, and Adults) volunteered to participate in this study. The characteristics of the subjects are shown in Table 1. The Under-15 and Under-18 soccer and basketball players competed in the Spanish first division of their respective categories. The adult soccer players competed in the Spanish third division, whereas the adult basketball players competed in the Spanish fourth division. The subjects had more than 5 (Under-15), 7 (Under-18), and 10 (Adults) years of training experience, and they had been injury free for at least 6 months before participating in this study. None of the subjects were taking drugs, medications, or dietary supplements known to influence physical performance. Coaches and parents were informed about the different test procedures performed during the study. Parental/guardian consents for all players under the age of 18 involved in this investigation were obtained. All subjects were informed about the experimental procedures and potential risks before they provided their written informed consent. The study was conducted according to the Declaration of Helsinki and was approved by the Research Ethics Committee of Pablo de Olavide University.
Testing was performed in a single session, and it took place on an indoor synthetic surface. Subjects were asked to refrain from vigorous activity for 48 hour before the experiment. Testing sessions were performed at the same venue and time of day (±1 hour) for each group under the same environmental conditions (∼21° C and ∼60% humidity). After a standardized warm-up, all participants were evaluated using the battery of tests described above. Flight time (t) and acceleration due to gravity (g) were used to calculate the vertical jump height (h) of the center of gravity of the body as follows: h = t2 × g/8. All jumping tests were assessed with the same measuring tool (Optojump System; Microgate, Bolzano, Italy). The participants were asked to try to achieve the greatest vertical height possible in each jump. To ensure that the jump was completely vertical, the subjects were required to take off and land within the same area (Figure 1). If the subject did not take off or land within the designated area, the jump was not considered. Countermovement depth was self-selected by the subject. Strong verbal encouragement was provided during all tests to motivate participants to make a maximal effort. Three experienced researchers supervised the testing session to ensure correct and consistent landing techniques were used during jump tests: legs and hips extended until contact was made with the floor, because flexing the knees or hips before landing will delay contact with the floor, thus extending air time (19). Each protocol was explained and demonstrated before testing. In addition, 2 sets of 5 submaximal and 3 maximal practice attempts (3 minutes rest) for all tests were administered before testing. Three attempts were made for each jump test, with a minimum rest period of 45 seconds between each attempt. Five-minute rest between jump tests was allowed before performing the specific warm-up for the following jump test. The values for the 3 attempts at each jump type were recorded and used for reliability analysis, whereas the mean of 3 attempts was used for correlation analysis.
Two 20-m sprints, separated by 3 minutes rest, were performed on an indoor running track. Photocell timing gates (Polifemo Radio Light; Microgate) were placed at 0, 10, and 20 m so that the times to cover 0–10 m (T10), 0–20 m (T20), and 10–20 m (T10–20) could be determined. A standing start with the lead-off foot placed 1 m behind the first timing gate was used. The best of both attempts was kept for analysis. Warm-up consisted of 5 minutes of running at a self-selected intensity, 5 minutes of joint mobilization exercises, followed by several sets of progressively faster 30-m running accelerations. The CVs for T10, T20, and T10–20 were 1.9%, 1.6%, and 1.2%, respectively, and the ICCs were 0.93 (95% CI: 0.91–0.95), 0.99 (95% CI: 0.98–0.99), and 0.97 (95% CI: 0.97–0.98) for T10, T10–20, and T20, respectively.
Countermovement Jump and Abalakov Jump
A CMJ was performed with the subject standing in an upright position on an infrared timing system (Optojump System; Microgate) with the hand on the hips to avoid arm swings. A fast downward movement was immediately followed by a fast upward vertical movement as high as possible, all in one sequence. The same procedure was applied for the AJ, but this test was performed with a full arm swing.
Three-Step Approach With Two or One Leg Take-Off Vertical Jumps
These tests were performed with a standardized starting position, with the lead-off foot behind the starting line, which was placed 3 m behind the infrared timing system (Optojump System; Microgate). The subjects performed a 3 fast-step approach followed by a leap on either 2 (2-LEGS) or 1 leg (1-LEG) with arm swing (Figure 1). With regard to 2-LEGS, subjects selected their preferred landing style before performing the jump as either hop style (when both feet touch the ground at the same time) or step-close style (where the second foot takes longer to make contact with the ground) because there were no differences between these styles in terms of performance and reliability (16).
Isoinertial Squat Loading Test
The assessment consisted of an isoinertial test with increasing loads using the FS exercise performed on a Smith machine (Multipower Fitness Line; Peroga, Murcia, Spain). Subjects started from the upright position with the knees and hips fully extended, stance approximately shoulder-width apart, and the barbell resting across the back at the level of the acromion. Each subject descended in a continuous motion until the top of the thighs went below the horizontal (ground) plane, with the posterior thighs and the back of the leg (calf) making contact with each other, then immediately reversed motion and ascended back to the upright position. Unlike the eccentric phase that was performed at controlled velocity (range: 0.50–0.65 m·s−1), subjects were required to always execute the concentric phase of each repetition at maximal intended velocity. A dynamic measurement system (T-Force System; Ergotech, Murcia, Spain) consisting of a cable-extension linear velocity transducer interfaced to a personal computer by means of a 14-bit resolution analog-to-digital data acquisition board and specialized software, automatically calculated the relevant kinematic and kinetic parameters of every repetition, provided real-time information on screen and stored data on disk for subsequent analysis (31). Vertical instantaneous velocity (v) was sampled at a frequency of 1,000 Hz and subsequently smoothed with a fourth-order low-pass Butterworth filter with a cutoff frequency of 10 Hz. The reliability of this system has been recently reported elsewhere (30). The velocity measures used in this study correspond to the mean velocity of the propulsive phase (mean propulsive velocity [MPV]) of each repetition (31). The propulsive phase was defined as that portion of the concentric phase during which the measured acceleration is greater than acceleration due to gravity (i.e., a ≥ −9.81 m·s−2) (31). The warm-up consisted of 2 sets of 8 repetitions without extra load, followed by 1 set of 6 repetitions with a 20-kg load. The initial load in the test was set at 20 kg for all subjects and was gradually increased in 10 kg increments until the attained MPV was ∼0.8 m·s−1. Thereafter, the load was adjusted with smaller increments (5 down to 1 kg) so that MPV was ∼1.00 m·s−1 (range: 0.95–1.05 m·s−1). This load was chosen because it has recently been shown that movement velocity has a very close relationship with the percentage of one-repetition maximum (1RM) (14). The participants performed 3 repetitions with each load. Only the best repetition at each load, according to the criteria of fastest MPV, was considered for subsequent analysis. The interset recovery time was 3 minutes. Estimated 1RM (1RMest) was calculated from the MPV with the last load (kg) of the test as follows: 100 × LOAD/−2.185 × MPV2 − 61.53 × MPV + 122.5; R2 = 0.96; Standard estimation error (SEE) = 5.5% (29).
Standard statistical methods were used for the calculation of mean values and SDs. A 1-way repeated-measures analysis of variance (ANOVA) was used to detect differences between the 3 attempts of all 4 jump tests (4). Absolute and relative reliability was assessed for each vertical jump test. A 1-way random-effects model (model 2,1) ICC with absolute agreement was used to determine relative reliability (39). The size of the correlation was evaluated as follows: r < 0.7 low; 0.7 ≤ r < 0.9 moderate, and r ≥ 0.9 high (39). Absolute reliability was reported using the standard error of measurement (40). The SEM values were expressed as a percentage of their respective mean values through the CV (4,18). Previous reliability studies (5,9) have reported biomechanical variables with CVs in the vicinity of 10% as reliable. As a result, a CV of ≤10% was set as the criterion to declare a variable as reliable. The minimal difference (MD) was determined per variable using the equation:
The MD values were expressed as a percentage of their respective mean values (MD [%]). A principal component analysis was used to report the amount of underlying sets of test types, determined by the Kaiser-Guttman criterion as an indicator of factorial validity. Pearson's correlation coefficients were calculated to establish the respective relationships between all variables measured. Correlation coefficient scores were converted to z-scores, using Fisher transformations to analyze the differences between these correlations. Statistical significance was set at p ≤ 0.05. All data analyses were performed using SPSS (V18.0; SPSS, Inc., Chicago, IL, USA).
The descriptive data for all 3 attempts and the average of each individual's mean value across all attempts of each test are presented in Table 2. One-way repeated-measures ANOVA only revealed significant (p ≤ 0.05) differences between the jump height for attempts 1 and 3 for the AJ in U-15 basketball players.
All 4 jump tests were found to have very high absolute and relative reliability, regardless of sport and age of players (Table 3). The CMJ and AJ tests were the most reliable vertical jump tests in soccer players, with ICC values higher than 0.989, and SEM and CV values ranging from 0.61–0.84 cm and 1.54–2.60%, respectively. In basketball players, the 2-LEGS test also showed very good reliability with ICC (0.994–0.995) and CV (2.12–2.40%) values similar to or even greater than those for the CMJ and AJ tests (ICC: 0.989–0.995; CV: 2.15–2.70%). The 1-LEG test was the vertical jump test with lowest absolute and relative reliability, showing higher SEM, CV, and MD scores and lower ICC scores than the other 3 vertical jump tests in both soccer and basketball players (Table 3).
All vertical jump tests were positively and strongly associated to one another, with the highest correlation coefficient values existing between the CMJ, AJ, and 2-LEGS tests in both soccer and basketball players (Table 4). The 1-LEG test showed the closest relationship with 2-LEGS (r = 0.71–0.97), whereas the correlations with the CMJ (r = 0.58–0.92) and AJ tests (r = 0.60–0.98) were significantly lower (p ≤ 0.05) compared with those shown between CMJ and AJ tests. The principal component factor analysis for all 4 vertical jump tests resulted in the extraction of one significant component, which explained 82.9–93.4%, and 90.7–95.8% of the total variance of all tests for soccer and basketball players, respectively. Correlation coefficients of all tests with the extracted component were high with values of 0.790–0.983 for soccer players and 0.920–0.987 for basketball players (Table 5).
Correlation coefficient values between the different vertical jump tests and acceleration capacity and maximal leg strength are displayed in Table 6. All correlations were significant, except the relationship between 1-LEG and sprint times in adult soccer players. The magnitude of the correlations was similar for all 4 vertical jump tests, with the 1-LEG test showing significantly lower associations with T10–20 compared with the CMJ (p ≤ 0.05), AJ (p ≤ 0.05), and 2-LEGS (p < 0.01) tests. The 1-LEG test also showed significantly lower correlation coefficient scores in T20 (p < 0.01) and 1RMest (p < 0.01) than the CMJ test. The best predictors of sprint time and 1RM for U-15 soccer players were the 2-LEGS and CMJ tests, and for U-15 basketball players, the CMJ and AJ tests. For U-18 soccer players, the best predictor of sprint time and 1RM was the CMJ test, whereas for U-18 basketball players, it was the 2-LEGS test. For the most part, the 2-LEGS assessment was the best predictor of sprint and strength performance in both adult soccer and basketball players.
The main finding of this study was that all 4 vertical jump tests showed a high absolute and relative reliability, regardless of age and sport practiced, although the 1-LEG test exhibited a slightly greater variability compared with CMJ, AJ, and 2-LEGS tests. Furthermore, both standardized and sport-specific vertical jump tests showed a moderate to high interrelationship, and within a heterogeneous sample, all vertical jump tests assessed the same physical attribute, as only a single principal factor was found. Finally, our results also showed that the CMJ, AJ, 2-LEGS, and 1-LEG tests yielded similar correlation values with sprint and maximal leg strength performance. We consider that these findings could have important practical applications. Thereby, if different jump tests are strongly interrelated and show similar relationships with other performance tests, sport scientists and strength and conditioning professionals do not need to perform a wide variety of jumps to assess the physical capacity of different athletes. In this case, it is sufficient to use only 1 vertical jump test; namely, the one that shows the greatest reliability.
The results of this study showed no significant differences in the average jump height between attempts for any vertical jump tests in any age group, except for AJ in U-15 basketball players (Table 2). Considering the high coordinative demands of the vertical jumping task (especially in 2-LEGS and 1-LEG tests), the interattempt variability was very low. These results are in line with a previous study (32). However, other studies analyzing reliability in different jumps and change of direction tests (23,35,36) have shown small but significant systematic variations in the average values of the attempts in the same test series, showing potentially worse performance in the first attempt. These studies (23,35,36) suggest that a motor learning effect could be present and indicate that, regardless of the population and the ability tested, one or more maximal test attempts should precede the testing to reduce motor learning effects. In this study, 3 maximal attempts were performed before testing; thus, the results of our study suggest that this possible motor learning effect was minimized.
Although the reliability of different vertical jump tests has been previously studied, to the best of our knowledge, this is the first study that has compared the reliability of 2 standardized and 2 sport-specific vertical jump tests in different sports players (soccer and basketball) across a wide age range (U-15, U-18, and adults). Overall, both standard and sport-specific vertical jump tests showed a very high reliability, with no apparent differences either between sports or between age categories (Table 3). However, the 1-LEG test tended to show slightly lower ICC values, and higher SEM, CV, and MD values than the other jump tests. The observed lower reliability recorded in the 1-LEG test compared with the other 3 vertical jump tests was probably the result of the more complex motor structure of this type of jump.
The reliability of different standardized vertical jump tests such as the CMJ and AJ has been widely studied in both young (1,38) and adult individuals (3,9,28,32,34). Most of these studies involved physically active individuals (3,23,25,34), but few studies have been conducted with high-performance athletes (9,28,32,38). In accordance with the abovementioned studies, our results established that CMJ and AJ tests resulted in high reliability in both soccer and basketball players. These results were to be expected, as all the subjects participated in sports requiring jumping; therefore, it can be supposed that the subjects had acquired the necessary competence in the motor skills required in these tests (25). Unlike the CMJ and AJ tests, the reliability of different sport-specific vertical jump tests has been less well studied (28,32). In these studies (28,32), ICC (0.97) and CV (2.5–2.8%) values were similar to those shown in this study (Table 3). Furthermore, a standardized 2-leg vertical jump test (CMJ) was also assessed in these studies (28,32), showing a trend toward a lower variability (ICC: 0.97–0.99; CV: 1.4–2.6%) than sport-specific jump tests, similar to our study.
Because 2 types of jump tests were performed (standardized and sport specific), we hypothesized that our tests might identify 2 separate factors for jumping performance. However, factor analysis resulted in the extraction of only 1 significant principal component that explained ∼82–95% of the variance for all 4 jumping tests. Because all jumping tests had high correlation coefficients with the principal component (r = 0.790–0.986; Table 5), we interpreted this factor as the explosive force or power ability. These findings are in accordance with previous studies (23,32) in which researchers performed factor analyses and identified a single latent dimension for explosive power. The correlation between the tests and the extracted factor represents the test's factorial validity (23); thus, it seems that the 2 standardized vertical jump tests and the 2-LEGS test have the best, and the 1-LEG test has the worst factorial validity. These results were similar for both soccer and basketball players and for all age groups. However, the results of the correlation analysis indicated that all 4 vertical jump tests were highly intercorrelated, although the greatest relationships were found between CMJ, AJ, and 2-LEGS (Table 4). These results reinforce the fact that all 4 vertical jump tests represent the same explosive force factor. Previous studies (23,24,32) have also shown significant correlation values between standardized and sport-specific vertical jump tests, although these correlation values were notably lower than those found in this study. In contrast, a recent study (28) showed no significant relationship between a traditional standing vertical jump test (CMJ) and a soccer-specific vertical jump, similar to the 1-LEG test in this study, either in flight time or take-off velocity. The differences with our results could be due to the use of different equipment to measure the jumps or in subtle differences in the jump protocols between studies. For example, Requena et al. (28) used jumps employing a parabolic trajectory, which is likely to introduce greater variability than jumps using a fully vertical displacement.
The secondary aim of this study was to analyze what type of jump test could predict functional performance. In this regard, our results showed that all 4 vertical jump tests showed a moderate to strong relationship with T10, T10–20, T20, and 1RMest (Table 6). The magnitude of these relationships was similar for all jump tests. However, converting these correlations to z-scores, using Fisher transformations, revealed the 1-LEG test tended to show significantly lower correlation coefficient values with T20, T10-20, and 1RMest than CMJ, AJ, and 2-LEGS, especially in soccer players (Table 6). This fact was in opposition to our hypothesis, as greater biomechanical similarities seem to exist between the 1-LEG test and running sprint (e.g., previous run phase, knee and ankle joints; force applied with one foot; shorter ground contact time) than between 2 legs take-off jump tests and sprint.
Previous studies analyzing the relationship between vertical jump and sprint ability typically used the standardized vertical jump tests (CMJ and SJ) and were conducted only with adults (2,7,8,10,21,24,41). To the best of our knowledge, there are no studies that analyze the relationships between sport-specific vertical jump tests, straight sprint, and maximal strength performance in soccer and basketball players of different ages. In line with this study, previous studies analyzing the relationship between CMJ performance and sprint ability in soccer, basketball, or other athletes have also shown a positive correlation between both variables (2,7,10,21,22,24). These relationships are in agreement with those biomechanical analyses of sprinting that indicate that short-distance sprint performance is highly dependent on the subject's ability to generate powerful extensions of the knee extensor, hip extensor, and plantar flexor muscles (12). Interestingly, in the abovementioned studies (2,7,10,21), the shorter the distance covered, the lower was the correlation value between CMJ and sprint time, which suggest that tests involving stretch-shortening cycles seem to be the least appropriate to assess performance in short-distance sprints, as the sprint start is heavily reliant on concentric force production (42). However, this did not seem to occur in this study, where the relationships between the different jump tests and T10, T10–20, and T20 were very similar, regardless of the sport and the age of the players. With regard to the relationship between jump tests and strength performance, previous studies reported similar correlations between squat strength and CMJ performance in adult male players of different sports (8,41). Although the authors acknowledge that a strong correlation does not imply a cause-effect relationship, several studies noted that increases in CMJ were accompanied by improvements in short sprint performance and muscle strength (13,15). Thus, our results confirm that the CMJ test is a good predictor of maximal and explosive strength capacity.
In summary, the results of this study indicate that both standardized vertical jump tests, the AJ test and particularly the CMJ test, are more reliable tests for the estimation of explosive force of the lower limbs in soccer and basketball players of different age categories than the 2 specific vertical jump tests. Despite these findings, this study has some limitations that need to be addressed. Obviously, the main limitation of this study is that only the within-day reliability was evaluated. Thus, the between-days reliability of all 4 vertical jump tests remains unknown. Although both within- and between-days reliability are parameters needed to define the reliability of a test, it seems that within-day reliability constitutes a more important parameter; if a test shows low absolute and relative reliability in a single session, it would not make sense to evaluate the between-days reliability. Therefore, pending further investigations, our results represent the first step toward understanding the reliability and the correlation with physical performance of different vertical jump tests. Another limitation of this study was that jump tests were performed in a fixed sequence for all participants: CMJ, AJ, 2-LEGS, and 1-LEG. Thus, although all participants were familiarized with the jump protocols and significant rest periods between attempts (∼1 minute) and between jump tests (5 minutes) were allowed during the testing session, it is possible that fatigue or other carry-over factors as a result of not using a counterbalanced design in the order of the vertical jump tests might have affected the reliability and correlation scores. Therefore, further investigations are needed to determine the between-days reliability and the influence of the order of conducting tests in both standardized and sport-specific jump vertical jump tests.
Several critical implications for coaches may be derived from this investigation to optimize the assessment of explosive force of the lower limbs. First, both standardized and sport-specific vertical jump tests have acceptable absolute and relative reliability, so they can be used for the estimation of jumping capabilities in soccer and basketball players of different ages. Second, considering that all 4 tests assess the same physical component and considering also that the CMJ, AJ, and 2-LEGS tests showed similar correlation coefficient values with sprint and maximal strength performance, it seems that only 1 test is required to evaluate an athlete's ability to fast force generation. Based on these results, strength and conditioning professionals are advised to use CMJ to determine the physical characteristics of athletes, at least in soccer and basketball players over the age of 14 years.
The authors have no professional relationships with companies or manufacturers that might benefit from the results of this study. There was no financial support for this project. The results of this study do not constitute endorsement of any product by the authors or by the National Strength and Conditioning Association.
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