The sport of basketball is demanding and requires speed, agility, upper and lower body strength, maximal aerobic power, and aerobic endurance. Basketball is a popular sport in the United States. At the high school level, 556,269 boys and 456,967 girls participated in this activity during the 2006–2007 academic year (9). Unfortunately, the benefits of playing may be offset with injuries, and female athletes appear to be at a greater risk than male athletes are (1,9). Specifically, Agel et al. (1) reported a significant difference in the rate of noncontact anterior cruciate ligament (ACL) ruptures over a 13-year period (1990–2002) between female and male collegiate basketball players (0.16 and 0.04 injuries per 1,000 exposures, p < 0.01). Hootman et al. (25) also reported a difference in the ACL injury rate over a 16-year period between female and male athletes involved in collegiate basketball (0.23 and 0.07 per 1,000 athlete exposures, p not available).
To our knowledge, only 1 investigation assessed the effects of a neuromuscular retraining program (Sportsmetrics, Cincinnati Sportsmedicine Research and Education Foundation, Cincinnati, OH, USA) in reducing the rate of occurrence of ACL injuries in female high school basketball players (23). The study included 84 female participants who completed the training program, 189 female participants who did not undergo training, and 225 male control players. The number of player exposures was 4,767 for the trained female group, 10,370 for the female control group, and 13,039 for the male control group. Four noncontact ACL injuries occurred in the female control group, compared with none in the other 2 groups. Untrained female players had significantly more noncontact knee ligament injuries than did the male players (p = 0.03).
Many basketball training programs have been developed to improve player fitness and skill and hypothetically prevent injuries (10,13,17,18,26,31,33,34,43,44). Investigations vary considerably in the selection of subjects, duration of training, exercises and drills performed, and outcome measures. Only one study to date assessed performance indices in female basketball players using the Sportsmetrics training program (44). A small group of female collegiate basketball players obtained significant improvements in hamstring peak torque (p = 0.008), which were not found in the control group of players. Development of hamstrings strength is believed to be one important factor in preventing knee ligament injuries in female athletes (2,21,40).
We initiated Sportsmetrics neuromuscular training for female athletes involved in a variety of sports 15 years ago (23) and noted occasional problems with player compliance with the program. The training consisted of a dynamic warm-up, jump training, strength training, and flexibility. Over time, players and coaches requested that the program be modified to include additional sport-specific exercises and drills designed to improve speed, agility, strength (upper extremity, lower extremity, and core), and aerobic conditioning. In addition, other investigators noted that improved compliance with injury prevention training programs would most likely occur if the programs target performance enhancement and neuromuscular retraining (3,27). Therefore, to increase player compliance and participation, we developed sports-specific programs for competitive female high school players involved in basketball (5), soccer (5), lacrosse, volleyball (36), and tennis (4). These training programs included the essential Sportsmetrics neuromuscular retraining principles previously proven to decrease the rate of noncontact ACL injuries in female athletes, along with other sports-specific exercises and drills. All the athletes who participated were enrolled in prospective studies in which neuromuscular and performance indices were measured before and upon completion of the training program.
For basketball, analysis of games demonstrate the importance of endurance, muscular strength and power, sprint speed, agility, and jumping ability (14,32). The goal of this study was to determine if the Sportsmetrics basketball training program was effective in improving neuromuscular and performance indices, thereby allowing recommendation for the program from both an injury prevention and performance enhancement standpoint. We hypothesized that this program would improve lower limb alignment on a drop-jump test from a valgus to a more neutral alignment, enhance estimated maximal aerobic power (O2max), increase vertical jump height, and improve sprinting speed in high school female basketball players.
Experimental Approach to the Problem
This study was undertaken to determine if a sports-specific training program could improve neuromuscular and performance indices in female high school basketball players. A program was devised, which used the dynamic warm-up, jump training, strength training, and flexibility components from a previously published ACL injury prevention program (5), along with new exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. A battery of tests was conducted to determine the effectiveness of this training program in improving lower limb alignment on a drop-jump test, estimated O2max, vertical jump height, and sprinting speed. Improved lower limb alignment while landing on a drop-jump test is believed by others to decrease the risk of occurrence of a noncontact ACL injury (24), although O2max, vertical jump height, and sprinting speed are essential components of this sport.
The athletes who participated in this study were high school female basketball players. All the subjects underwent a video drop-jump test, a multistage fitness test (MSFT), a countermovement vertical jump test, and an 18-m sprint test before the neuromuscular training program was initiated. The subjects then participated in the program 3 sessions per week on Mondays, Wednesday, and Fridays for 6 weeks. The sessions lasted approximately 90–120 minutes and consisted of a dynamic warm-up, jump training, strength training, speed, and agility drills specific for basketball and flexibility. All the training sessions were supervised by certified Sportsmetrics instructors and were conducted on the schools' basketball court and weight room facilities during the summer off-season or in the fall just before the start of their season. The subjects underwent all of the previously described tests within 1 week of conclusion of the training program in an identical manner as that done before the training program was initiated. All the subjects participated in their high school basketball season upon the completion of the training program.
All testing and training procedures were fully explained, and written informed parental consent was obtained for each subject. The study was approved by an Internal Review Board for use of human subjects. A total of 57 female basketball players (14–17 years of age; height, 170.8 ± 7 cm, range, 160–188 cm; weight, 60.7 ± 10.1 kg, range, 51.6–72.5 kg; mean body mass index 20.3 ± 3.4, range, 17.2–30.3) voluntarily participated in this study. None of the subjects had participated in a formal neuromuscular or resistance training program, but all had at least 1 season of experience. There were no athletes with a history of knee injury or pathology, symptoms of pain, patella instability, or a visible knee joint effusion.
Video Drop-Jump Test
A video drop-jump test was done as previously described in detail (6,36). The subjects performed a drop-jump sequence by first jumping off a box 30.48 cm in height, landing, and immediately performing a maximum countermovement vertical jump. No specific instructions were provided regarding how to land or jump; the subjects were only instructed to land straight in front of the box. This sequence was repeated 3 times. Three images were captured that represented the preland, land, and take-off phases. The absolute centimeters of separation distance between the right and left hips, knees, and ankles was measured, and the distance between the knees and ankles was normalized according to the hip separation distance (Figure 1). The data were also distributed into 3 categories for analysis: ≤60% normalized knee separation distance, 61–80%, and >80%. The reliability of the drop-jump test has been reported previously (36). For the test-retest and within-test trials, the interclass correlation coefficients (ICCs) for the hip, knee, and ankle separation distances were all ≥0.90.
Multistage Fitness Test
O2max was estimated using the MSFT (30,38). The subjects were required to perform a shuttle run back and forth along 20 m, keeping in time with a series of signals on a compact disk by touching the appropriate end line in time with each audio signal. The frequency of the audible signals (and hence running speed) was progressively increased until the subjects reached volitional exhaustion and could no longer maintain pace with the audio signals. O2max was estimated using regression equations described by Ramsbottom et al. (38). The test-retest reliability of the MSFT has been reported by others to be sufficient, with ICCs ≥ 0.90 (20,30,45). The data were also placed into categories of poor, fair, good, and excellent/superior of the estimated O2max for female participants aged 13–19 years as determined by the American College of Sports Medicine (19). The categories indicated by poor represent <31.0 estimated O2max; fair, 31.0–34.9; good, 35.0–38.9; and excellent/superior, ≥39.0.
Vertical Jump Test
The subjects' countermovement vertical jump was measured using a Vertec Jump Training System (Sports Imports, Columbus, OH, USA). First, the standing reach was measured. Then, a countermovement maximum jump with arm swing was performed 3 times and the highest jump obtained recorded. The reliability for the assessment of vertical jump height using the Vertec was reported by others to be excellent, with ICCs of 0.92 (11) and 0.94 (46).
Eighteen-meter Sprint Test
Sprint speed was assessed by an 18-m sprint test. A distance of 18 m was measured on the basketball court with the start and finish lines clearly marked with masking tape or cones. The subjects were instructed to sprint as fast as possible through the finish line, making sure not to slow down before crossing the line. Each athlete completed 1 sprint, and the time was recorded with a digital stopwatch in one-hundredths of a second.
Neuromuscular Retraining Program
The subjects participated in a modified Sportsmetrics Basketball (Cincinnati Sportsmedicine Research and Education Foundation) training program. The training comprised a dynamic warm-up, jump training, and flexibility exercises described previously (5). In addition, strength, agility, acceleration, speed, and endurance drills were added to specifically target the requirements of competitive basketball players (Table 1). All the training sessions were conducted by certified instructors; there were 3 sessions per week (on nonconsecutive days) for 6 weeks, and all were done in the afternoon upon completion of school. Each session lasted approximately 90–120 minutes and was conducted at the schools' basketball court and weight room facilities. The instructors kept logs of all exercises completed during each training session.
The dynamic warm-up was consistent throughout all the sessions and included heel-toe walking, straight leg marching, leg cradle walking, dog and bush walking, and high knee skipping for half a court. In addition, high knees and glut kicks, stride-out running, and all-out sprinting were done for 1 full court.
During the jump training and speed and agility drills, the subjects were instructed and reminded to maintain a neutral overall alignment. Verbal cues were given to keep the knees and ankles hip distance apart and to use exaggerated knee and hip flexion when landing from a jump, decelerating, and cutting. Trainers gave constant feedback on jump-land mechanics as previously described (5). Strength training focused on hamstring, hip flexion/abduction, core, abdominal, and shoulder musculatures to aid in proper lower extremity alignment and muscle recruitment patterns. The subjects performed strength training in a weight room using machines, free weights, a cable system, and body weight exercises. At the end of each session, flexibility exercises were performed that targeted the hamstrings, quadriceps, iliotibial band, hip flexors, gastrocnemius/soleus, deltoid, triceps, pectoralis major, biceps, and low back.
For data that were normally distributed (Kolmogorov-Smirnov test), a 2-tailed paired t-test was used to detect the differences between the 2 test periods. Data that failed the normality test were assessed with Wilcoxon matched-pairs signed-ranks tests. Chi-square analyses were used to compare the distribution of the subjects in the percentile rank subcategories before and after training in the MSFT and in the 3 normalized knee separation distance categories (≤60, 61–80, and >80%) in the drop-jump test. Effect sizes were calculated and interpreted according to Cohen's standards (13). Power and sample size were calculated to evaluate the effect of training on the normalized knee separation distances. With 57 subjects in this study, it was found that this investigation had sufficient power (>90%) to detect significant differences in normalized knee separation distances (at least 15 ± 1%) and in estimated O2max values (at least 5 ± 1) at a level of 0.05. For all comparisons, a level of p ≤ 0.05 was considered to be statistically significant.
In the video drop-jump test, statistically significant increases were found between pretrained and posttrained test sessions on landing in the mean absolute knee separation distance (p < 0.0001), the mean normalized knee separation distance (p < 0.0001), and in the distribution of the subjects in the normalized knee separation distance categories (p < 0.0001, Table 2, Figure 2). Improvement in the normalized knee separation distance was demonstrated in 91% of the subjects.
A statistically significant improvement was found in the mean estimated O2max score (p < 0.0001) and in the difference in the distribution of the subjects in the categories between pretrain and posttrain test sessions (p < 0.0001, Figure 3). Eighty-nine percent of the subjects improved this score.
A significant improvement was found in the vertical jump test (p < 0.0001), as 70% of the subjects increased their scores. However, the effect size was small (0.09). There was no significant improvement in the 18-m sprint test. No subject sustained an injury that resulted in loss of time training or that required formal medical attention. All the subjects attended at least 14 of the 18 training sessions.
This investigation measured the effects of a basketball neuromuscular and performance enhancement training program in high school female athletes aged 14–17 years on lower limb alignment on a video drop-jump test, estimated O2max, vertical jump height, and sprint speed. The training program was unique in that it combined components from a published ACL injury prevention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. The main findings of this study were a significant increase in the mean estimated O2max and improved lower limb alignment on landing from a drop jump. Aerobic fitness is paramount in basketball, because players will experience fatigue as the game progresses, which can negatively affect performance (7). Improvement in lower limb alignment on a drop jump from a valgus position to a more neutral position is believed to be beneficial in preventing noncontact ACL injuries (24,39).
The motivation for our investigation stemmed from the desire expressed by athletes and coaches to broaden the existing Sportsmetrics ACL prevention training program to include speed, agility, and aerobic conditioning geared toward basketball. In addition, other authors have speculated that improved compliance with knee injury prevention training programs would most likely occur if the programs focused on performance enhancement and neuromuscular retraining and we agreed with this approach (3,27). Our study demonstrated excellent athlete participation because 18 players (31%) attended 14–15 sessions, 22 (38%) players attended 15 sessions, and 17 players (30%) attended 17–18 sessions.
In this investigation, 88% of the athletes had ≤60% normalized knee separation distance on landing from a drop jump before training, indicating a distinct valgus lower limb alignment. This lower limb alignment is believed to be a potential risk factor for a future noncontact ACL injury and the International Olympic Committee recommended use of the drop-jump test to identify athletes at-risk for a noncontact ACL injury (39). Stensrud et al. (41) reported that a subjective interpretation of knee control on landing during this test provided a useful screening tool for identifying athletes with poor lower limb mechanics. Studies that analyzed ACL injuries using video analysis of the actual event commonly described a valgus knee position that was present either milliseconds before, after, or at the time of the ligament rupture (8,28,29). After training, only 27% of the subjects in our study continued to show such poor knee separation distances. One study showed that improvements in overall lower limb alignment on the drop-jump test were retained up to 1 year after Sportsmetrics training in a group of high school volleyball players (6). Future studies are required in basketball players to determine if a similar retention effect occurs. The drop-jump video test provides a general indicator of an athletes' lower limb axial alignment in the coronal plane because it shows the position of the hips, knees, and ankles in a single plane during 1 task (37). It is important to note that many noncontact ACL injuries usually occur in side-to-side, cutting, or multiple complex motions in more than 1 plane.
In this study, 52% of the subjects were either in the poor (17%) or fair (35%) MSFT categories before training. Improvements were found in 89% of the subjects and after training, only 14% were in the poor or fair categories. The MSFT has been used in many investigations to determine the cardiovascular fitness levels of children aged 6–19 years (42), junior rugby league players (20), elite junior male basketball players (7,16), average junior-level male basketball players (16), and youth soccer players (45) and is recommended by the American College of Sports Medicine (19) as a valid and reliable method to estimate O2max. We were unable to find any other study that assessed the effects of a neuromuscular and performance intervention training program using MSFT data in female high school basketball players.
Improvements were found in 70% of our subjects for the vertical jump tests; however, the effect size was small, and the increases ranged from 1 to 9.5 cm (mean, 2.3 cm). Chappell and Limpisvasti (10) reported significant increases in vertical jump height in a study consisting of 12 collegiate female basketball players and 18 collegiate female soccer players. The athletes participated in a 15-minute warm-up program that included core strength, single-leg passing, and 3 jumps before each practice during their season. Vertical jump height increased 7%, from 45.1 ± 14.1 to 48.8 ± 13.9 cm (p < 0.001) after training. These results are not comparable with those of this study because they involved Division I collegiate athletes and included soccer players. Athletes who do not improve their vertical jump height may benefit from different plyometric exercises than those used in the program in the current investigation. De Villarreal et al. (15) summarized data from 56 studies that assessed the effects of plyometric training on improving vertical jump height and concluded that a combination of squat, countermovement, and depth jumps was significantly more effective than the use of a single plyometric exercise (p < 0.05) (15). The overall enhancement in vertical jump height after training was 3.90 cm or approximately 7%. Advanced plyometric training does carry the risk of injury or the development of an overuse syndrome. We believe that athletes must first be taught proper jump and landing techniques through the neuromuscular training program described in this investigation before performing advanced plyometrics. In addition, supervision is required to ensure the athlete performs the exercises safely and correctly.
Six other investigations of ACL injury prevention programs (10,26,31,33,43,44) and 2 general injury prevention programs (17,34) designed for female basketball players have been published to date (Table 3). These studies demonstrated success in reducing vertical ground reaction forces during jumping (43) and in improving isokinetic knee flexor peak torque (44); knee flexion angle, knee separation distance, and valgus moments on a rebound jump task (31); static and dynamic balance (33); dynamic lower limb alignment control during a stop jump shot (26); and knee flexion on a drop jump (10). Two of these studies assessed the effects of the Sportsmetrics training program on neuromuscular and performance enhancement factors. Wilkerson et al. (44) conducted this program in 11 female collegiate basketball players during preseason conditioning sessions. After training, a significant increase was measured in hamstrings peak torque at 60°·s−1 (pretrain, 90.81 ± 17.91 N·m and posttrain, 98.12 ± 20.91 N·m, p = 0.008), with every subject showing improvement. Vescovi et al. (43) implemented the plyometric jump retraining portion of Sportsmetrics in 10 collegiate female basketball players 3 times a week for 6 weeks during an intramural basketball league season. Compared with a control group of 10 collegiate female players, the experimental group demonstrated reductions in vertical ground reaction forces during a countermovement jump. Specifically, 8 of the 10 trained athletes showed a mean reduction of 478.8 ± 325.0 N. There was no difference in the absolute change in values between groups for countermovement vertical jump height or other associated kinetic variables. The study was limited by the small sample size and the absence of the strength and flexibility portions of the Sportsmetrics program.
One limitation to our study was that there was no control or comparison group, which will be included in future studies. We did not control for activities athletes may have been involved in before training; however, none had participated in a neuromuscular training program, and none were playing organized basketball at the time the training was initiated. Additional studies are required to determine if this program also reduces the incidence of noncontact ACL injuries during basketball practice and competition. In addition, it remains to be determined if this program results in improved player performance during competition. The program was conducted in female high school basketball players of varying experience levels, and the results may not be applicable to elite or collegiate players. There was no improvement in sprint time; however, this may be because of the use of a digital stopwatch for a short distance. Although a digital stopwatch may be appropriate for tests of longer distances, such as the 200-m sprint as analyzed by Hetzler et al. (22), it may not be sensitive enough to detect significant differences for the 18-m sprint used in our study.
The findings of this study indicate the effectiveness of a new basketball training program in female high school athletes. The program combines components from a previously published ACL injury prevention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. This program may be conducted in the off-season or just before the beginning of the high school basketball season. All training is done on a high school basketball court and weight room. We recommend that coaches and trainers who wish to implement this program conduct the tests that were done in this study to determine the overall effectiveness of the program. Athletes who fail to improve should be encouraged to continue neuromuscular training.
The authors acknowledge Tony Rolinski, Director of Strength and Conditioning for Olympic Sports, University of Notre Dame for the Figure 4 drill, shoot and sprint, and Irish “D” drills; and Bigger Faster Stronger, Inc. (Salt Lake City, UT, USA) for the dot drills.
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Keywords:© 2012 National Strength and Conditioning Association
drop-jump; ACL; lower limb alignment