In basketball, improving jumping abilities markedly enhances individual competitive performance. In basketball, players most often jump when shooting and rebounding. When shooting, a player must dribble the ball while avoiding defenders and follow the rules of basketball without traveling, and then put the ball through the basket. Additionally, depending on defender actions, a shooter must decide whether to jump with 1 or 2 legs. The most common example of shooting with a 1-legged takeoff on an approach run is to drive to the basket and shoot a lay-up; the most common example of shooting with a 2-legged takeoff on an approach run is to drive to the basket and shoot a jump shot. A dunk may be performed with either a 1-legged or a 2-legged takeoff. These jumping abilities involve jumping height and contact time. In competition, if an offensive player can jump high and quickly, then this player is more likely to disrupt the timing of defenders (10), draw a foul, and shoot the ball. When comparing running 1-legged and 2-legged vertical jumps, there is no marked difference in jumping height, but a running 1-legged vertical jump has a shorter contact time (16,21). In studies on the running 1-legged vertical jump, there have been reports on the high jump and long jump in track and field, but because people compete for height and distance in these athletic events, there have not been many studies that analyzed contact time as 1 of the factors determining jumping performance (2,13,14).
Any movement that exerts explosive power, such as the running 1-legged vertical jump, is referred to as a ballistic movement, and its neurological control mechanisms are different from movements that take a relatively long time to execute, such as the running 2-legged vertical jump in which the knees are flexed deeply (6). Additionally, in the running 1-legged vertical jump, motor unit mobilization and neurological stimulation of muscles enable quick movements (9,17).
From the viewpoint of muscle contraction, the running 1-legged vertical jump is a stretch-shortening cycle movement characterized by a high level of eccentric muscle contraction occurring immediately after landing, which is immediately followed by concentric muscle contraction. The stretch-shortening cycle facilitates the regulatory mechanism of nerves, muscles, and tendons in terms of the stretch reflex mechanism (9) and elastic energy storage and reuse (1,4,5). It exerts a large amount of force quickly from the beginning and improves motor efficiency.
This information suggests that the running 1-legged vertical jump in basketball requires comprehensive abilities to efficiently carry out ballistic and stretch-shortening cycle movements.
With the drop jump, in which a person jumps off of a stand, lands, and then immediately jumps, and with the repeated rebound jump, in which a person successively and quickly jumps vertically (19,22), a basic jumping index that was calculated based on contact time and jumping height (jumping height/contact time) has been used to assess ballistic stretch-shortening cycle movements (23,24). Many studies on basketball players have analyzed jumping techniques (11,12,26), but there have only been a few studies that measured a jumping index (3).
In the present study, the aforementioned assessment method was applied to assess the abilities to jump higher and shorten the contact time of the running 1-legged vertical jump in an attempt to ascertain determination factors and efficacy. In addition, we compared basic jump performances, in which the subject was asked to jump in different techniques, with the running 1-legged vertical jump performance. These basic jumps were performed without an approach run and were classified by the combination or 2-legged or 1-legged takeoff with deep or shallow knee bending. The hypotheses were that a subject's ability to perform a running vertical jump in basketball could be effectively assessed with the jumping index; that there is a basic jump that is effective in improving both contact time and jumping height, the 2 components of the jumping index in the running 1-legged vertical jump; and that the basic jump is a jumping technique resembling the running 1-legged vertical jump motion.
Experimental Approach to the Problem
Each subject was asked to perform several jumps: a lay-up shot jump (LSJ), in which the subject ran toward the basket and jumped with a 1-legged takeoff for a basketball lay-up shot, and basic jumps in which the subject was asked to jump in different ways. The types of basic jumps were countermovement vertical jump (CMJ), 2-legged repeated rebound jump (TRRJ), and 1-legged repeated rebound jump (ORRJ). The independent variables in this study were maximum jumping height, contact time, and jumping index in LSJ. The dependent variables in this study were maximum jumping height; contact time (except for CMJ); and jumping index (except for CMJ) in CMJ, TRRJ, and ORRJ.
Subjects were 19 male university basketball team players who were selected to play in a national collegiate tournament (32 teams) in Japan in 2006. Their mean (±SD) height was 176.9 ± 7.0 cm, body weight was 68.9 ± 7.3 kg, and age was 19.6 ± 1.3 years. All subjects had played basketball for at least 5 years. The subjects volunteered to participate in this study. The subjects were tested after 1 week in a major collegiate tournament. No subjects were currently suffering any lower-extremity injury that would prevent them from completing the testing jumps. All subjects were informed of the experimental risks and signed an informed consent document prior to the investigation. This investigation was approved by an Institutional Review Board for the use of human subjects.
In LSJ, the subject was placed 6 m from the center of the basket (height: 3.05 m) and was asked to take 2 steps and jump with a 1-legged takeoff for a lay-up without the basketball. In the present study, tests were conducted without the basketball to eliminate various constraint conditions, and this allowed the subjects to fully concentrate on jumping. Additionally, the subjects were asked to run toward the basket so that they could maximize their jumps (7,13-15). All subjects took off on the leg opposite from the hand used for shooting the basketball. The subjects were instructed to imitate a lay-up and jump as high as possible.
In basic jumps, the subjects were asked to perform CMJ and repeated rebound jumps (RRJ) (19,22). The CMJ was the vertical jump from an erect standing position with a preliminary countermovement. In this test, the subjects were instructed to jump as high as possible. The RRJ were repeated vertical jumps with a rebound movement similar to bouncing a ball and were performed with 2 legs (TRRJ) or 1 leg (ORRJ). In this test, the subjects were instructed to jump as fast and as high as possible. Before measurements were taken, the subjects sufficiently practiced these jumps.
Jumping heights and contact times (except for CMJ) were measured using a contact mat/computer system (8,19,24). In each test, the subjects jumped on a contact mat (66 × 100 cm). In LSJ, because takeoff and landing sites markedly differed, 2 mats were placed near the takeoff site and 4 mats were placed near the landing site. The contact mat/computer system read the ON and OFF signals during foot contact on the ground and the flight of the body in milliseconds. Contact, takeoff, and landing times were recorded to calculate contact time (Tcon, sec) and air time (Tair, sec). The contact times for TRRJ, ORRJ, and LSJ were indicated as TRRJtc, ORRJtc, and LSJtc, respectively. Jumping height was calculated using the free-fall formula (H = 1/8 g·Tair2). Furthermore, “g” was gravitational acceleration with a value of 9.81 m/sec2. The jumping heights for TRRJ, ORRJ, LSJ, and CMJ were indicated as TRRJh, ORRJh, LSJh, and CMJh, respectively. Jumping index was calculated by dividing the jumping height by the corresponding contact time (jumping height/contact time) and indicates power. The jumping index for TRRJ, ORRJ, and LSJ were indicated as TRRJindex, ORRJindex, and LSJindex, respectively. These data were immediately displayed and feedback was provided after each trial. Tests were invalid if the feet were off the mats.
In LSJ and CMJ, 3 valid measurements were taken and data from the highest jumps were used (19). In TRRJ and ORRJ, the subjects swung their arms to continuously perform 5 repeated rebound jumps (19,22) and each test was repeated twice. From 10 measurements, the highest jumping index was used for analysis (19).
Numerical data were expressed as mean ± SD. One-way analysis of variance (ANOVA) was used to compare data among the different jumping tests. Items with significant F values were further subjected by Scheffe multiple comparison analysis. Pearson correlation analysis was used to compare parameters. In all analyses, the level of significance was set at p < 0.05. The within-session reliability for each variable was calculated with an intraclass correlation coefficient (LSJh, R = 0.818; LSJtc, R = 0.886; LSJindex, R = 0.861; TRRJh, R = 0.849; TRRJtc, R = 0.797; TRRJindex, R = 0.846; ORRJh, R = 0.718; ORRJtc, R = 0.780; ORRJindex, R = 0.839; CMJh, R = 0.928).
Comparison of LSJ, ORRJ, TRRJ, and CMJ Measurements
Table 1 lists the mean (±SD) for LSJ, ORRJ, TRRJ, and CMJ. The jumping height was the highest LSJh, followed by CMJh, TRRJh, and ORRJh, in that order (p < 0.001). The contact time was the highest TRRJtc, followed by LSJtc and ORRJtc, in that order (p < 0.001). The LSJindex was significantly greater than TRRJindex (p < 0.05), and ORRJindex was significantly smaller than that LSJindex or TRRJindex (p < 0.001).
Interrelationships Among LSJindex, LSJtc, and LSJh
Figure 1 shows the interrelationships among LSJindex, LSJtc, and LSJh. A significant correlation existed between LSJtc and LSJindex (r = −0.700, p < 0.001) and between LSJh and LSJindex (r = 0.678, p < 0.01). However, no significant correlation existed between LSJtc and LSJh (r = 0.041, ns).
Relationship of LSJ to ORRJ, TRRJ, and CMJ in Terms of Jumping Index, Contact Time, and Jumping Height
Figure 2 shows the relationship of LSJ to ORRJ, TRRJ, and CMJ in terms of jumping index, contact time, and jumping height. Regarding jumping index, a significant correlation existed between ORRJindex and LSJindex (r = 0.614, p < 0.01) and between TRRJindex and LSJindex (r = 0.509, p < 0.05). Regarding contact time, a significant correlation existed between ORRJtc and LSJtc (r = 0.472, p < 0.05) and between TRRJtc and LSJtc (r = 0.567, p < 0.05). Regarding jumping height, a significant correlation existed between ORRJh and LSJh (r = 0.570, p < 0.05). However, no significant correlation existed between TRRJh and LSJh (r = 0.305, ns) or between CMJh and LSJh (r = 0.360, ns).
In the present study, we first compared LSJ, a typical running 1-legged vertical jump in basketball, to basic jumps that are generally used to assess jumping abilities (Table 1). The results showed that the LSJh was significantly higher than those for the basic jumps and the LSJindex was also significantly higher. Hence, LSJ was the jumping technique with the highest jumping index. However, LSJtc was significantly longer than that TRRJtc. Aura and Viitasalo reported that the average contact time for the high jump was 177 ms (2), and Stefanyshyn and Nigg reported that the average contact time for the long jump ranged from 150 to 170 ms (18). The average LSJtc was 217.5 ms in the present study, which was shorter when compared to past study results of 230 to 250 ms (18).
The lay-up shot jump index (LSJindex) is a parameter that is calculated based on the contact time (LSJtc) and jumping height (LSJh) of LSJ. As shown in Figure 1, a significant correlation existed between LSJindex and LSJtc and between LSJindex and LSJh. However, no significant correlation existed between LSJtc and LSJh, thus confirming that these 2 variables are mutually independent. These results show that LSJtc represents the ability to shorten the muscle action and LSJh represents the ability to acquire the jumping height, and, as a result, contact time and jumping height are mutually independent abilities. Therefore, when examining LSJ, it is important to separately analyze contact time and jumping height.
In the present study, LSJ was compared to basic jumps (ORRJ, TRRJ, and CMJ) in terms of jumping index, contact time, and jumping height (Figure 2). The results showed that LSJindex correlated more closely to ORRJindex than TRRJindex, but LSJtc correlated more closely to TRRJtc then ORRJtc. Furthermore, a significant correlation was seen in jumping height between ORRJh and LSJh, but not between LSJh and TRRJh or between LSJh and CMJh.
The 2-legged drop jump is a typical reactive strength movement, and this jump is important for improving the running 1-legged vertical jump and assessing jumping abilities (25). The present study clarified that TRRJ is a training technique that is effective in improving LSJtc. However, LSJindex correlated more closely to ORRJindex than TRRJindex and no significant correlation existed between TRRJh and LSJh. The reason for this was that both ORRJ and LSJ required subjects to jump with 1 leg, and when compared to TRRJ, ORRJ more closely resembled LSJ in terms of movement characteristics. In addition, no significant correlation existed between CMJh and LSJh, and the reason for this was that CMJ was a low-intensity movement with a low stretch-shortening cycle, whereas LSJ was a ballistic high-intensity movement with a high stretch-shortening cycle. This suggests that effective training must follow the principle of specificity.
Furthermore, a significant positive relationship existed between ORRJ and LSJ in terms of contact time and jumping height. This indicates that people with quick ORRJ also have quick LSJ and those with high ORRJ height have high LSJ height. Aura and Viitasalo compared the 1-legged drop jump (ODJ) and high jump and reported that because the 2 jumps had different contact times, ODJ was not suited for high jump training (2). When compared to high jump and ODJ, LSJ and ORRJ share more similarities: there is a significant correlation in contact time between LSJ and ORRJ, whereas both high jump and LSJ are 1-legged jumping movements with an approach run; the contact time for LSJ is longer; and the contact time for a rebound jump is significantly shorter when compared to a drop jump (22). Additionally, in the subject with the shortest ORRJtc, the difference between ORRJtc and LSJtc was small (17 ms). These findings suggest that ORRJ is the most effective technique that can improve both contact time and jumping height for LSJ. Furthermore, in vertical jump, the maximum flexion angles for the knee and hip joints for a 1-legged takeoff phase are greater when compared to a 2-legged takeoff phase (20), thus suggesting that the maximum flexion angles for the knee and hip joints for ORRJ are greater when compared to TRRJ. Hence, TRRJ with slight knee bending movements is suited for strengthening the stiffness of the ankle joint (22) and compared to TRRJ, ORRJ is a movement that more fully involves the knee and hip joint muscles.
In the future, it will be necessary to shorten the contact time and improve the jumping height in LSJ and further analyze the relationship of LSJ to ORRJ as a training technique.
The results confirmed that LSJindex is useful for assessing the jumping ability of basketball players using a running 1-legged vertical jump. The LSJ ability consists of 2 independent factors: contact time and jumping height. Therefore, when improving LSJ, it is necessary to train to improve these 2 factors. ORRJ was shown to be an effective basic jump technique in improving both contact time and jumping height in LSJ. These findings are useful for evaluating ability to perform running 1-legged vertical jumps in basketball and examining training techniques to improve ability to perform running 1-legged vertical jumps in basketball.
The authors would like to acknowledge funding support from the National Institute of Fitness and Sports in Kanoya. We would also like to thank the athletes from the National Institute of Fitness and Sports in Kanoya for participating in this project.
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