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Original Research

Biomechanical Differences of Multidirectional Jump Landings Among Female Basketball and Soccer Players

Taylor, Jeffrey B.1,2; Ford, Kevin R.1; Schmitz, Randy J.2; Ross, Scott E.2; Ackerman, Terry A.3; Shultz, Sandra J.2

Author Information
Journal of Strength and Conditioning Research: November 2017 - Volume 31 - Issue 11 - p 3034-3045
doi: 10.1519/JSC.0000000000001785
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Abstract

Introduction

Of women's high school team sports, basketball and soccer have among the highest rates of general lower extremity and anterior cruciate ligament (ACL) injuries (19). Although both sports possess relatively high risks of injury, women's basketball players experience higher rates of ACL tears from a noncontact mechanism than women's soccer players (1) and are more likely to experience severe concomitant injuries (13). Although this suggests a critical need for ACL injury prevention programs in women's basketball players, these programs are more commonly administered and reported to be substantially more successful in women's soccer populations (26,28,32). Current ACL injury prevention programs are administered as nonspecific, “one size fits all” training regimens, with minimal regard for sport differences in movement strategies, activity demands, mechanism of injury, or the way athletes may respond to a neuromuscular preventive training program. Likely, a combination of these factors may help elucidate why ACL injury prevention programs have been more successful in soccer than basketball and can help with the design of future sport-specific programs.

To date, limited research has compared movement strategies between basketball and soccer players. Of these few studies, basketball players are reported to perform jump landings with higher vertical ground reaction forces over a shorter timeframe than soccer players, while soccer players exhibit higher forces during cutting maneuvers (8). These differences are important, considering athletes who experience ACL injuries land with 20% higher ground reaction forces than noninjured athletes (17). In addition, basketball players have been reported to exhibit greater levels of frontal plane motion during single-leg landings than soccer players (27), which has also been prospectively identified to be significantly larger in athletes who subsequently tear their ACL (17). Although these studies indicate that women's basketball players exhibit higher-risk movement strategies than soccer players during some athletic tasks, these comparisons have been limited to analyses of jump landing activities performed predominantly in the sagittal plane, using tasks such as drop vertical jumps (DVJs) and single-leg drop landings (8,27). Previous research indicates that lower extremity biomechanics change as the movement plane and direction of movement change (37,38) and that movement strategies during sagittal plane activities do not predict movement strategies employed during other tasks (20,22). Considering that both basketball and soccer are multidirectional sports that require a large frequency of movements outside the sagittal plane, strictly sagittal plane tasks may not provide a comprehensive view of high-risk biomechanics in these athletes. As such, biomechanical analyses of activities outside the sagittal plane may be particularly important in women's basketball players, because they more often perform lateral movements than sagittal plane movements (25) and more often perform lateral movements than soccer players over the course of a standard competition (3).

A more detailed analysis of the difference in fundamental movement strategies between basketball and soccer players during a variety of jump landings in and out of the sagittal plane is necessary to understand the reason for poor success of ACL injury prevention programs in women's basketball players and to move forward with future sport-specific injury prevention programs. Therefore, the purpose of this study was to better characterize hip and knee biomechanics (peak joint angles, joint excursions, external joint moments, and energetics) between competitive female basketball and soccer players during a standard double-leg screening test in the sagittal plane and during double- and single-leg jump landing tasks in the frontal plane. Based on previous biomechanical analyses of sagittal plane activities (8), we hypothesized that basketball players would generate higher hip and knee joint moments and stiffness measures than soccer players. Furthermore, we anticipated that these relationships would be more prevalent during frontal than sagittal plane and single- than double-leg jump landings.

Methods

Experimental Approach to the Problem

This study was part of a larger injury prevention study that identified neuromuscular changes after an ACL injury prevention program. The current analyses used a cross-sectional design to identify differences in lower extremity biomechanics (dependent variables) between athletes participating in basketball and soccer (independent variable).

Subjects

Ninety-nine female athletes participated in the study (Table 1). To be included, participants were required to (a) be middle and high school athletes between age 13 and 19 years, (b) consider basketball or soccer as their primary sport, (c) be fully cleared to participate in sports, and (d) have no lower extremity injury at the time of testing. Potential participants were excluded if they reported a lower extremity surgery within the past 6 months or had been previously diagnosed with a vestibular, balance, or cardiac disorder. Participants were enrolled in the study after providing written informed parental consent, and participant assent on forms approved by the institutional review boards at the primary author's institutions. Ten athletes who participated in the study were excluded from this analysis because they had actively participated in both basketball and soccer during the previous academic year, leaving a total of 89 single-sport participants (age 13–18 years, n = 40 basketball, n = 49 soccer) in this study. A power analysis was performed for the main aim of this study, revealing that 80 participants were required to obtain adequate power for the repeated measures design to analyze between sport differences. Thus, with 89 participants, this study had sufficient power for its cross-sectional design.

Table 1.
Table 1.:
Mean ± SDs of anthropometric and sport history variables.*

All participants were tested during their off-season yet were still practicing with their teams. Each athlete completed an electronic questionnaire utilizing REDCap electronic capture tools (14) to determine the athlete's sport history, including the number of years, months per year, and days per week that they typically participate in their primary sport.

Procedures

Instrumentation

Each subject was instrumented for 3-dimensional analysis with 43 retroreflective markers on their trunk, pelvis, and upper and lower extremities as has been previously published (38). To standardize footwear, all participants donned laboratory-provided athletic footwear not specific to either sport (adidas adipure 360.2; Adidas, Beaverton, OR, USA). After instrumentation, a static trial in anatomic neutral stance was collected to determine each subject's neutral alignment and anatomically define each body segment, by which subsequent biomechanical measures were referenced. Three-dimensional motion data, sampled at 200 Hz, were collected with Cortex software (version 5; Motion Analysis Corporation, Santa Rosa, CA, USA) using a 14-camera system (Eagle cameras; Motion Analysis Corporation). Kinetic data, sampled at 1,200 Hz, were collected by dual, in-ground, multiaxis force plates (AMTI, Watertown, MA, USA), such that each force plate collected data from a single leg.

Jump Landing Tasks

Because the main focus of this study was to identify potential reasons for higher injury risk and reduced efficacy of ACL injury prevention programs in basketball players, only the biomechanics of jumping and landing were analyzed. A ball was placed directly over the force plates at the participant's maximal vertical jump reach to encourage maximal effort during each trial. (11) This height was determined by having participants perform 3–5 repetitions of a maximal effort double-leg countermovement jump before testing. Participants then completed 3 trials of 5 different jump landing tasks in a random order (Figures 1 and 2): (a) DVJ, (b) double-leg forward jump and maximum countermovement jump in the sagittal plane (SAG-DL), (c) single-leg forward hop and maximal countermovement hop in the sagittal plane (SAG-SL), (d) double-leg lateral jump and maximum countermovement jump in the frontal plane (FRONT-DL), and (e) single-leg lateral hop and maximum countermovement hop in the frontal plane (FRONT-SL). The DVJ is the gold-standard jump landing screening task used in clinical practice and research and has evidence that the biomechanical movement patterns it elicits may be predictive of ACL injury (17). The other 4 tasks were selected based on their good-to-excellent reliability and day-to-day performance consistency (38), and their basketball-specific demands that are consistent with the single-leg and frontal plane jump landings that occur during competition and at the time of ACL injury (4,23,25). Each participant performed 1–3 practice trials of each jump landing, until the subject was comfortable with the task and the investigator deemed the performance adequate. After the practice trials, each task was performed 3 times, while lower extremity biomechanics were recorded for analysis. To avoid fatigue, athletes were given self-selected rest intervals ranging from 10 to 20 seconds between jumps and 60–90 seconds between tasks, resulting in a total of 27 jumping trials over an average of 13 minutes. In addition, we calculated the coefficient of variation of vertical jump height performance during 3 trials of the DVJ, finding that the average was less than 3% (maximum = 8.4%), which indicated minimal signs of fatigue.

Figure 1.
Figure 1.:
Sagittal-plane jump landing tasks used in this study, including the beginning and landing phases of the drop vertical jump (A and B), double-leg forward jump and maximum countermovement jump in the sagittal plane (C and D), and single-leg forward hop and maximal countermovement hop in the sagittal plane (E and F).
Figure 2.
Figure 2.:
Frontal-plane jump landing tasks used in this study, including the beginning and landing phases of the double-leg (A and B) and single-leg (C and D) lateral hop and maximum countermovement hop in the frontal plane.

The DVJ was performed with the participant standing on top of a 31-cm box with their feet spaced 35-cm apart. Participants were instructed to drop straight down, land evenly on both feet, and immediately perform a maximal-effort double-leg countermovement jump, reaching for the target with both hands. For the SAG-DL task, participants started at a distance equal to their leg length (greater trochanter to lateral malleolus) away from the front edge of the force plates. Participants were then instructed to jump forward with both feet, aiming to land symmetrically with each foot on a separate force plate, and immediately perform a maximal countermovement jump, reaching up for the target with both hands. Similar methods were used for the SAG-SL task, although the subject was positioned at a distance equal to one-half of their leg length away from the force plates and were asked to hop off a single-leg, land on the same leg, and immediately perform a maximal countermovement hop, attempting to reach the target with the contralateral hand. The contralateral upper extremity was used as the reaching arm because it most resembled athletic movements of multidirectional jumping sports. The SAG-SL task was performed 3 times on each leg in a randomized order.

The FRONT-DL task was a lateral jump with double-leg landing and immediate maximal countermovement jump. The subject was positioned, such that they were straddling a line placed at a distance equal to one-half of their leg length away from the lateral edge of the nearest force plate. The subject was then instructed to keep their trunk facing forward and jump laterally, such that each foot landed simultaneously on a separate force plate, and immediately perform a maximal countermovement jump, reaching for the target with both hands. Similar techniques were used for the FRONT-SL task. Subjects were again placed at a distance equal to one-half of their leg length away from the closest force plate, standing on their outside leg. The subject was instructed to hop to the middle of the second force plate (located 36 cm plus one-half of leg length away), land on the opposite limb, and immediately perform a maximal countermovement hop, reaching toward the target with the hand contralateral to the landing limb.

Limb Dominance

Considering that the dominant limb is most often injured (5), lower extremity biomechanics from each subject's dominant limb were used for analysis. The definition of limb dominance may vary between sports, especially considering the different sport-specific demands associated with basketball and soccer. Thus, rather than using the standard definition based on kicking leg preference, limb dominance was defined in this study based on performance during a triple hop for distance test, as performance hopping tests have been reported to best identify limb asymmetries (12). Participants were instructed to perform 3 consecutive maximal forward hops on the same limb without hesitation. One to 3 practice trials were given (self-selected) on each leg, and the next 3 subsequent test trials were recorded by measuring the distance from the starting line to the point of toe contact on completing the third hop. The order of limbs was counterbalanced for each subject. Trials were repeated if the participant lost balance or contacted the ground with their opposing leg at any instance throughout the test. Three trials on each leg were recorded, and the leg which produced the longest maximal hop was subsequently defined as the dominant limb.

Data Analysis and Reduction

Biomechanical data were processed in Visual3D (Version 5; C-Motion, Inc., Rockville, MD, USA) with custom MATLAB (Version 8.0; The Mathworks, Natick, MA, USA) code. Hip joint centers were calculated using the Bell method (2), and the knee and ankle joint centers were calculated as the centroid position of the medial and lateral femoral epicondyles and malleoli, respectively. Joint angle and moment data were subjected to a low-pass fourth-order Butterworth filter with a cutoff frequency of 12 Hz. Hip flexion, adduction, and internal rotation and knee extension, adduction, and internal rotation were reduced as positive motions.

Kinematic variables of interest were peak angles for hip flexion, adduction, and internal rotation, and knee flexion, abduction, and internal and external rotation and joint excursions for hip flexion, adduction, and internal rotation and knee flexion, abduction, and internal and external rotation. Joint excursions were calculated by subtracting the angle at initial contact (first point that vertical ground reaction force surpasses 10 N) from the peak angle during the landing phase (initial contact to maximal descent of the center of gravity). Kinetic variables included peak external moments (hip flexion, adduction, and internal rotation and knee flexion, abduction, and internal and external rotation) that were normalized to height and mass (N·m/m·kg). Joint energetics, including sagittal-plane hip and knee energy absorption and torsional joint stiffness, were also analyzed. To calculate energy absorption, net joint powers for each time point were first calculated (normalized joint moment × joint angular velocity) separately for hip and knee flexion. The area under the negative portion of the joint power curve was defined as the energy absorption that occurred by the hip and knee extensors (J/[N·m]; reported as positive values for interpretation). Torsional joint stiffness was calculated as the change in sagittal-plane net moment divided by joint excursion during the landing phase at both the hip and the knee (N·m/[N·m·degrees]). These biomechanical variables were selected based on their potential to contribute to injurious mechanics at the time of ACL injury in female athletes (4,15,18,23,33,35). Mean values of all successful trials for each task were calculated and used in statistical analyses. Trials were excluded if the athlete did not land on the intended force plate or if tracking markers were covered and unidentifiable during a trial, which accounted for less than 5% of trials in this study. To enable visual comparisons of the sport differences during each task, ensemble curves of select variables were generated in MATLAB by normalizing each variable to the duration of ground contact during the task.

Statistical Analyses

Anthropometric differences between basketball and soccer players were identified using independent t-tests. Then, 4 separate multivariate analysis of variance models were performed to test for differences in the following: (a) peak angles, (b) excursions, (c) joint moments, and (d) energetics between basketball and soccer players for each task. Multivariate statistical significance was analyzed using Wilk's Lambda followed up with post hoc pairwise comparison using independent t-tests as appropriate. Cohen's d effect sizes were calculated for all significant biomechanical differences between basketball and soccer players. Statistical significance was set a priori for all analyses at α = 0.05.

Results

Descriptive anthropometric and activity history data are reported in Table 1. Although there was no significant difference in age between basketball and soccer participants (p = 0.83), basketball players were taller (p < 0.001), heavier (p < 0.001), and had higher body mass index (p = 0.01). Basketball players had fewer years of experience participating in their sport than soccer players (p < 0.001), but there were no differences in current training volume (p > 0.05).

Biomechanical Comparisons

Mean values and SDs of all hip and knee kinematic, kinetic, and energetic data are reported for each jump landing task in Tables 2 and 3.

Table 2.
Table 2.:
Mean ± SDs of kinematic variables for each jump landing task for BB and SOC players.*
Table 3.
Table 3.:
Mean ± SDs of kinetic variables for each jump landing task for BB and SOC players.*

Kinematics

There were no significant differences between sports in peak kinematic variables for any of the double-leg landings (DVJ: λ = 0.91, p = 0.32; SAG-DL: λ = 0.91, p = 0.40; FRONT-DL: λ = 0.86, p = 0.08); however, significant differences were identified during single-leg landings (SAG-SL: λ = 0.83, p = 0.03; FRONT-SL: λ = 0.75, p = 0.001), where basketball players landed with greater peak hip flexion angles during the SAG-SL (p = 0.04, d = 0.45) and lesser hip adduction angles during the FRONT-SL (p < 0.001, d = 0.82) task.

Sport differences in total joint excursion were identified during each jump landing task (DVJ: λ = 0.84, p = 0.04; SAG-DL: λ = 0.80, p = 0.01; SAG-SL: λ = 0.79, p = 0.006; FRONT-DL: λ = 0.80, p = 0.009; FRONT-SL: λ = 0.76, p = 0.002). These differences were predominantly found in sagittal-plane joint motions (Figure 3), where basketball players went through less hip flexion during the DVJ (p = 0.047, d = 0.43), SAG-DL (p = 0.002, d = 0.69), FRONT-DL (p < 0.001, d = 0.82), and FRONT-SL (p = 0.03, d = 0.48) tasks and less knee flexion during the SAG-DL (p = 0.002, d = 0.70), SAG-SL (p = 0.003, d = 0.65), FRONT-DL (p < 0.001, d = 0.80), and FRONT-SL (p = 0.01, d = 0.56) tasks. Basketball players also went through greater relative knee external rotation during the DVJ (p = 0.05, d = 0.42) and internal rotation during the SAG-SL (p = 0.05, d = 0.43) than soccer players. In the FRONT-SL task (Figure 4), basketball players (in addition to less hip and knee flexion already noted) went through more hip internal rotation (p = 0.003, d = 0.67), knee external rotation (p = 0.001, d = 0.76), and less knee internal rotation (p = 0.005, d = 0.62) than soccer players.

Figure 3.
Figure 3.:
Ensemble curves of (A) hip and (B) knee flexion angles for each jump landing task. SAG-DL = double-leg forward jump and maximum countermovement jump in the sagittal plane; SAG-SL = single-leg forward hop and maximal countermovement hop in the sagittal plane; FRONT-DL = double-leg lateral jump and maximum countermovement jump in the frontal plane; FRONT-SL = single-leg lateral hop and maximum countermovement hop in the frontal plane.
Figure 4.
Figure 4.:
Ensemble curves of frontal and transverse plane angles and moments at the hip and knee during the single-leg lateral hop and maximum countermovement hop in the frontal plane task. abd = abduction; add = adduction; IR = internal rotation; ER = external rotation.

Kinetics

No significant differences in joint moments were found during double-leg landings (DVJ: λ = 0.90, p = 0.29; SAG-DL: λ = 0.90, p = 0.27; FRONT-DL: λ = 0.86, p = 0.09), yet significant differences were identified during the SAG-SL (λ = 0.85, p = 0.05) and FRONT-SL (λ = 0.75, p = 0.001) tasks. Specifically, during the SAG-SL task, basketball players had greater hip internal rotation (p = 0.02, d = 0.55) and knee abduction (p = 0.02, d = 0.47) moments and greater knee abduction (p = 0.003, d = 0.76), less hip adduction (p = 0.001, d = 0.71) and less knee external rotation moments (p < 0.001, d = 0.78) during the FRONT-SL task than soccer players (Figure 4).

Energetics

Significant differences in hip and knee energetics were identified during the FRONT-DL task (λ = 0.77, p < 0.001), such that basketball players absorbed less energy at their hip (p < 0.001, d = 0.94) and exhibited greater stiffness at the hip (p < 0.001, d = 0.80) and knee (p = 0.001, d = 0.67) than soccer players. No significant differences in energetics were identified during the DVJ (λ = 0.91, p = 0.10), SAG-DL (λ = 0.89, p = 0.055), SAG-SL (λ = 0.96, p = 0.42), or FRONT-SL (λ = 0.91, p = 0.09) tasks. A summary table depicting biomechanical differences between basketball and soccer players is found in Table 4.

Table 4.
Table 4.:
Summary table showing biomechanical differences between basketball and soccer players.*†‡

Discussion

Both women's basketball and soccer have relatively high ACL injury rates (19), but basketball players may be more at risk for noncontact injuries (1), and current prevention programs have been much less successful at reducing the risk of ACL injury in women's basketball (26,32,39). Because ACL injury prevention programs are designed to improve neuromuscular strategies to reduce high-risk movements, the poorer success of these programs in basketball suggests that either the training program is less effective at modifying high-risk biomechanics in basketball than soccer players or that women's basketball and soccer players employ different biomechanical profiles and may need sport-specific training to address these distinct movement strategies. Our findings indicate that it may be the latter, as we observed a number of fundamental differences in movement strategies between female basketball and soccer athletes, with the largest biomechanical differences identified during the most basketball-specific activity (FRONT-SL) because of its frontal plane and single-leg demands.

Our results indicate that soccer players tend to land with an overall more protective biomechanical strategy than basketball players. Specifically, basketball players consistently landed more stiffly, with less hip and knee flexion excursion, and during some tasks were more likely to land with greater hip internal rotation and knee external rotation angles and greater knee abduction moments (KAMs), which are commonly considered elements of dynamic knee valgus. These sport-specific biomechanical differences were more pronounced when the intensity and complexity of the task increased from double- to single-leg and sagittal to frontal plane activities. These findings expand on previous work that has reported larger forces (8) and knee valgus measures (27) during standard sagittal-plane jump landings in women's basketball compared with those in soccer players.

Shallow knee and hip flexion angles have been implicated as a risk factor for ACL injury (4,15,36). In our study, basketball players consistently displayed a stiffer landing strategy regardless of the task, but this difference approached 10° less hip and knee flexion motion during the FRONT-DL task. This may place basketball players at higher risk for ACL injury, because observational video analyses have reported that up to 90% of injured female athletes land with less than 30° of knee flexion at initial contact and exhibit relatively low knee flexion excursions from initial contact to the estimated onset of ACL rupture (7,23,29). This is also consistent with cadaveric and in vivo studies of ACL strain that report increased strain on the ACL between 0 and 30° of knee flexion (6,34). Although shallow knee flexion angles and excursions have been reported at the time of ACL injury, no study has prospectively linked this movement strategy during a screening test to risk of subsequent injury. However, because of the evidence supporting stiff-legged landings as a potential mechanism for ACL injury (17,29), our results indicate that basketball players may be at higher risk of injury during jump landing activities. Although ACL injury prevention programs already focus on increasing knee flexion and landing softly (24), sports medicine professionals may need to place greater emphasis on these strategies when training basketball players.

Although hip and knee joint excursions tended to be less in all tasks in female basketball players, sport differences in peak angles, moments, and energetics were mostly limited to frontal plane movements and single-leg landings. Previous studies comparing basketball and soccer players have only tested athletes during sagittal-plane jump landings. Using a DVJ, Cowley et al. (8) reported larger and shorter times to peak vertical ground reaction forces in basketball players, but minimal differences in kinematics or joint moments were identified between the 2 sets of athletes. Munro et al. (27) were limited to 2-dimensional analysis and used a single-leg drop landing, as opposed to a hop, although they were able to identify differences in frontal-plane projection angles. Our study provides a more comprehensive biomechanical comparison of basketball and soccer athletes, which may begin to elucidate why injury prevention programs are less successful in basketball athletes. Frontal plane movements, such as lateral shuffling, occur more frequently than running in women's basketball (25). In addition, basketball players often land asymmetrically (10,16), and because of the physical nature of the sport, are often perturbed before landing, potentially influencing their risk for injury (23). Thus, while most biomechanical analyses of injury risk and the adaptations after ACL injury prevention programs use standard double-leg tasks, our results indicate that a more comprehensive screen, including more complex tasks that incorporate frontal plane and single landings, is crucial in future investigations of populations that include women's basketball players.

Of all the jump landing tasks used in this study, the DVJ has the most evidence supporting its use for ACL injury risk screening (17), yet the FRONT-SL task was able to best discriminate between the biomechanical differences of basketball and soccer players. Although this task has not yet been validated, it has been shown to be a reliable task that provides additional complementary information to standard double-leg landings in the sagittal plane that may help create a more complete biomechanical profile (38). It also may be a task more representative of what occurs at the time of ACL injury. ACL injuries have been linked to single-leg ground contact, decelerating movements and change of directions (4,18,23), but the plane of movement has not been specifically studied. Observational video analyses of injured athletes have reported that athletes at the time of injury have tended to land with and stay in more hip abduction (27–30°) and ipsilateral lateral trunk lean (11°) than matched controls (4,18). While the reason for hip abduction in these cases is unknown, these values may suggest that the athletes were abducting their hip to widen the base of support in anticipation of a frontal plane change of direction. While these data again suggest that investigating the biomechanics of frontal plane landings may be extremely important during future injury risk studies, further exploration into diagonal and multiplanar hops may also be warranted.

Kinematically, the combination of less sagittal-plane hip and knee flexion excursion and greater transverse plane motion that was evident in women's basketball players is indicative of motions typically associated with dynamic lower extremity valgus, which may increase their risk of ACL injury. Consistent with this premise, basketball players had greater KAMs than soccer players during single-leg tasks, which has been reported to be predictive of ACL injury risk, albeit produced during a DVJ (17). Consistently landing with a stiff knee, in relatively low hip and knee flexion excursions, and higher KAM during these tasks may in part contribute to the heightened risk of noncontact ACL injury in basketball players, especially because basketball requires more frequent single-leg jump landings and frontal plane movements than soccer (3,25). Because ACL injury prevention programs emphasize sagittal plane movements and double-leg landings (39,40), they may not provide the appropriate stimulus to improve high-risk biomechanics during frontal-plane single-leg activities that is necessary to reduce risk in female basketball players. While basketball players often train to increase performance in the frontal plane (i.e., quickness in lateral shuffling), our results suggest that additional technique training and feedback may be warranted to increase knee and hip flexion angles and promote frontal and transverse plane hip and knee stability during these types of motions.

Adolescent female basketball players seem to have high-risk movement strategies during jump landings, hence the large proportion of ACL injuries that occur during landing (31). However, one might expect basketball players to exhibit superior biomechanics during jumping because of the high demands present in the sport. One explanation may be their anthropometric characteristics. Female basketball players are taller and heavier than soccer players, and they may not possess adequate strength to coordinate their longer segments' lengths and larger mass. This may be especially true of those athletes who may have experienced a rapid growth spurt during their adolescent years. One other factor may be years of sport experience. Our basketball players had less experience in their sport than soccer players and may have not yet adapted to the demands of the game.

Although our data suggest that women's basketball players may land with more at-risk movement strategies, it does not diminish the risk that women's soccer players face during competition. While basketball players landed with a stiffer movement pattern, including lower hip and knee flexion peak angles and excursion values, it is interesting to note that the ensemble curves presented in Figures 3A, B indicate that soccer players landed with lower hip and knee flexion angles at initial contact across a majority of tasks. Because ACL injuries typically occur within 40 milliseconds of ground contact (21), biomechanical findings at initial contact may be a better reflection of the high-risk movement strategies associated with the ACL injury mechanism. In addition, past evidence shows that soccer players seem to be more at risk during cutting activities (9), which this study does not address. As such, sport-specific injury prevention programs that emphasize optimizing biomechanics during multiplanar double- and single-leg jump landings in basketball players and cutting soccer players deserve more attention.

The tasks used in this study can be reliably performed and have the potential to provide complementary information to standard screening tasks (38). However, other than the DVJ, these tasks are yet to be validated as effective prospective screening tools for ACL injury risk. Future research is needed to study the predictive ability of one or a combination of these tests to identify athletes at risk for subsequent ACL injury. Potentially using another validated tool, such as the Landing Error Scoring System, would help solidify the biomechanical differences reported in this study (30). In addition, this study was limited to characterizing biomechanical differences during more basketball-specific tasks to help explain differences in injury rates and the success of ACL injury prevention programs in these 2 sports. Although basketball consists of more jumping and frontal plane activities than soccer, soccer too has sport-specific demands, including cutting and change of direction, which are more prevalent than basketball. Thus, while this study now illustrates the biomechanical differences during jump landings, it did not analyze biomechanical sport differences during cutting activities, which may further help describe sport-specific biomechanical profiles.

Practical Applications

This study provides important practical value for sports medicine clinicians. Data indicate that basketball and soccer players exhibit distinct biomechanical profiles during a variety of movement tasks, with the largest differences appearing during tasks with more specificity to basketball than soccer, suggesting the need for greater consideration of the distinct sport demands and movement strategies when implementing rehabilitation, screening, or injury prevention programs. Specifically, basketball players may need a stronger emphasis placed on softer landing strategies to reduce forces and limit ACL strain that occurs at shallow knee flexion angles. In addition, basketball players may benefit from dedicated technique training during single-leg and frontal-plane jump landings. While basketball-specific training that incorporates movements outside the sagittal plane is prevalent during rehabilitation and return to sport procedures (41), this type of training has previously been lacking ACL injury prevention programs that typically use a nonspecific, “one size fits all” approach that does not account for these fundamental differences in movement strategies.

Acknowledgments

No funding was received for this work.

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Keywords:

sport-specific; frontal plane; single-leg; injury risk

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