Journal of Sport Rehabilitation, 2015, 24, 21-30 http://dx.doi.org/10.1123/jsr.2013-0099 © 2015 Human Kinetics, Inc.

www.JSR-Journal.com ORIGINAL RESEARCH REPORT

The Effect of a 3-Month Prevention Program on the Jump-Landing Technique in Basketball: A Randomized Controlled Trial Inne Aerts, Elke Cumps, Evert Verhagen, Bram Wuyts, Sam Van De Gucht, and Romain Meeusen Context: In jump-landing sports, the injury mechanism that most frequently results in an injury is the jumplanding movement. Influencing the movement patterns and biomechanical predisposing factors are supposed to decrease injury occurrence. Objectives: To evaluate the influence of a 3-mo coach-supervised jump-landing prevention program on jump-landing technique using the jump-landing scoring (JLS) system. Design: Randomized controlled trial. Setting: On-field. Participants: 116 athletes age 15–41 y, with 63 athletes in the control group and 53 athletes in the intervention group. Intervention: The intervention program in this randomized control trial was administered at the start of the basketball season 2010–11. The jump-landing training program, supervised by the athletic trainers, was performed for a period of 3 mo. Main Outcome Measures: The jump-landing technique was determined by registering the jump-landing technique of all athletes with the JLS system, pre- and postintervention. Results: After the prevention program, the athletes of the male and female intervention groups landed with a significantly less erect position than those in the control groups (P < .05). This was presented by a significant improvement in maximal hip flexion, maximal knee flexion, hip active range of motion, and knee active range of motion. Another important finding was that postintervention, knee valgus during landing diminished significantly (P < .05) in the female intervention group compared with their control group. Furthermore, the male intervention group significantly improved (P < .05) the scores of the JLS system from pre- to postintervention. Conclusion: Malalignments such as valgus position and insufficient knee flexion and hip flexion, previously identified as possible risk factors for lower-extremity injuries, improved significantly after the completion of the prevention program. The JLS system can help in identifying these malalignments. Level of Evidence: Therapy, prevention, level 1b. Keywords: lower extremity, injuries, injury High risks of injury are registered in volleyball, gymnastics, and basketball.1,2 In these sports, a high rate of jump-landing maneuvers with rapid decelerations and stops occurs.3–6 The studies of Borowski et al7 and Cumps et al4 found that, in basketball, the specific noncontactinjury mechanism that resulted the most frequently in injury was the jump-landing movement. The review of Aerts et al8 highlighted that different modifiable biomechanical and lower-extremity malalignments during jump landing are defined as possible risk factors for injury. Literature shows that individuals who land with less active hip flexion and knee flexion create more stress on Aerts, Verhagen, Wuyts, Van De Gucht, and Meeusen are with the Dept of Human Physiology and Sports Medicine, Vrije Universiteit Brussel, Brussels, Belgium. Cumps is with the Dept of Master of Physical Therapy in Sports, SOMT Stichting Opleidingen Musculoskeletale Therapie, Amersfoort, The Netherlands. Address author correspondence to Romain Meeusen at [email protected].

passive structures such as the ligaments and tendons of the lower extremity.9 Moreover, dynamic valgus of the knee during the jump landing10 is an important predictive parameter for acute lower-extremity injury. Even the ankle joint is an important component within the closed kinetic chain, as a decreased range of motion in dorsiflexion might limit the ability to land safely from a jump.9 There has been less research on the influence of jump-landing kinematics and its relationship with overuse injuries. Similar to the biomechanical risk factors for acute injuries, a jump landing with more hip extension and knee extension has been suggested to be a risk factor for patellar tendinopathy.11 Some studies also clearly indicate that limited ankle flexion12,13 and more ankle pronation14 are risk factors for the development of overuse injuries. Moreover, as literature suggests, gender differences are present in jump-landing technique, with females more susceptible to injuries.15,16 In general, jump-landing technique is measured in laboratory settings. Current laboratory technologies of 3-dimensional recordings of jump-landing movement

21

22  Aerts et al

detect the athlete at risk but are expensive and timeconsuming.10 Therefore, recent attempts are made to develop adequate on-field tools for coaches to implement screening strategies to detect athletes at risk. Those tools, however, only focused on a specific injury10,17 and cannot be used to screen the jump landing to predict athletes at risk for lower-extremity injury.18 Based on the biomechanical risk factors found in the literature, we have designed a jump-landing scoring (JLS) system that is meant to be helpful in the observation of the jumplanding technique in on-field situations in all types of jump-landing sports.19 This instrument is developed as an easily accessible tool for coaches and will enable the evaluation of the jump-landing technique of an athlete outside a laboratory setting. Literature10,20 indicates that a jump-landing technique can be trained and is therefore susceptible for changes. By influencing the biomechanical predisposing factors and malalignments,8 injuries will consequently be prevented.21 For that reason, a program aiming to improve jump-landing technique is potentially an important preventive measure, since it should be able to eliminate multiple risk factors as much as possible. Earlier attempts were made to investigate the effects of injury-prevention programs on lower-extremity kinematics during landing tasks,22,23 in which it was found that neuromuscular and balance training are effective methods for influencing lower-extremity biomechanics. Those studies, however, measured the jump-landing technique in a laboratory setting using expensive equipment.22,23 Furthermore, most available prevention programs are supervised by sports physicians or sports physical therapists,24 yet amateur sports lack the infrastructure and funds to have a sports physician or therapist to permanently supervise such an injury-prevention program. The true effectiveness of available preventive programs in this on-field setting still remains unclear. Hence it is important to provide prevention programs and screening tools that are inexpensive and easily implementable and consequently investigate their effectiveness in on-field settings. The objective of this randomized controlled trial study was to evaluate the effect of a coach-supervised jump-landing prevention program that was effective in the prevention of lower-extremity injuries by altering the jump-landing technique of the athletes25 measured by the JLS system. The jump-landing technique of both male and female athletes was investigated.

Methods Trial Design A randomized controlled trial was conducted at the start of the 2010–11 season and was performed in an on-field setting. The study was conducted in accordance with the ethical institutional rules for human research and with the Declaration of Helsinki for Medical Research involving human participants. Written informed consent was obtained from each athlete. This study is a part of a

broader study,8,19 the complete design of which is published in Aerts et al.19 During the study period there were 2 fixed times, at preintervention and after 3 months (postintervention), at which the athletes’ jump-landing technique was assessed. At preintervention all athletes completed a questionnaire on demographic data, previous injuries, sports history, and current sports participation.26 In addition, exposure hours and lower-extremity injuries were continuously registered during the entire 2010–11 basketball season.

Participants The participating subjects (N = 243) were athletes from basketball teams of the second and third national divisions and first and second regional (Flanders, Belgium) divisions of the Flemish basketball competition. We excluded athletes if they had not mastered the Dutch language or had an injury to the lower extremity before the intervention. Based on a power analysis, 24 teams of the 110 eligible Flemish teams were randomly assigned using computerized randomization.19 After this selection, the teams were randomized to a control group (CG) or an intervention group (IG) (Figure 1). Randomization and group allocation (1:1) took place before teams were contacted. If an allocated team was not willing to participate, the team was replaced with another team from the backup randomization list. This backup randomization list was provided to guarantee the required number of teams based on power analysis. This procedure was exactly the same for the IG and the CG. The CG was unaware of an existing IG and vice versa. This was done to avoid motivation bias, known as the Hawthorne effect.27

Interventions A personal visit by one of the involved researchers (sports physiotherapists) with each of the coaches was organized to inform them of the prevention program. During this meeting, the coaches of the intervention teams received a DVD with specific information on the program (pictures, videos, and instructions) on how to correctly instruct and perform the exercises. In addition, we provided a poster to the coaches with pictures of the exercises of the jumplanding program and handouts with written instructions. Both the IG and the CG were instructed not to alter their normal training amount or training strategy. Teams of the IG received, in addition to their regular training routine, a prevention program that had to be carried out during their warm-up twice a week, lasting 5 to 10 minutes per session. The prevention program (Table 1) aimed to improve the athletes’ jump-landing technique and lasted 3 months.19,25 In the first month the exercises focused on basic techniques such as squats, lunges and side-to-side jumps. In the second month, fundamental exercises such as tuck jumps, squat jumps, 1-leg jumps, and jumps on unstable ground were trained. Thereafter, in the performance phase, more-difficult and sport-specific exercises were given, such as maximal jumps and running

Intervention on Jump-Landing Technique  23

Figure 1 — Flowchart of selection procedures and the number of players and teams finally participating in the study. Abbreviations: T0, preintervention; T1, postintervention.

and cutting movements. The prevention program is based on the literature, more specifically on prevention programs aiming to prevent lower-extremity injuries.22,23 To perform the prevention program no extra equipment was needed, because in every gym the required equipment, such as benches and balls, was available. The researchers were appointed to weekly supervise whether all exercises of the prevention program were performed.

Outcome Measures The involved researchers asked the athletes to perform 3 separate maximal vertical jumps, which were recorded simultaneously on 3 high-definition cameras (Sony HDV 1080i; 60 Hz) in 2 different planes. The cameras were placed in the front and at both sides of the athlete at equal distances (280 cm) and at 100 cm high. During the trial, the only instruction given to the participants was to perform a 2-footed standing maximal countermove-

ment jump with emphasis placed on jumping as high as possible. It was important that both the takeoff and landing of the participants occurred in the square marked on the ground. No further instructions or feedback was provided. The participants performed the jumps with shoes but without socks. The rest of the outfit consisted of Spandex shorts and top for the female athletes, while the male athletes were bare-chested and also wore Spandex shorts. The recordings of the jumps (preintervention and postintervention) were all analyzed with the JLS system by the experienced data analyst, who was blinded to group allocation. In this procedure, Darttrainer was used to process the videos, which made it possible to freeze images, calculate angles, and detect alterations in lowerextremity mechanics.28 Preintervention and postintervention, jump-landing technique of the overall, male, and female athletes was measured using the JLS system. The JLS system consists of 35 different criteria measured in frontal and lateral

24  Aerts et al

Table 1  Overview of the Jump-Landing-Technique Program Week

Technique, month 1

Fundamentals, month 2

Performance, month 3

1

Cocontractions, 10 L + R

Lying position, 15

X-hops, 6 cycles L + R

Wall squat, 10 L + R

Pelvic bridge, 10 s

Hop-hop-hold, 8 L + R

Lateral jump and hold, 8 L + R

Repeated tuck jumps, 10 L + R

Mattress jumps, 30 s

Front lunges, 10

Squat jump, 10

Single-leg 90°,a 8 L + R

Step-hold, 8

Jump single-leg hold, 8

Max squat jumps-hold, 10 L + R

Cocontractions, 10 L + R

Pelvic-bridge single-leg, 10

Crossover-hop-hop-hold, 8 L + R

Squat, 10 L + R

Prone-bridge hip–shoulder flexion, 10 L+R

Single-leg 4-way hop-hold,a 3 Cycles L+R

Step-hold, 8 L + R

Side-to-side tuck jump, 10 s

Single-leg 90° ball,a 8 L + R

Walking lunges, 10

Lateral hop and hold, 8 L + R

Step, jump up, down, vertical jump, 5L+R

Lateral jump and hold, 8

Hop and hold, 8

Max squat jumps-hold, 10

2

3

4

bridge,a

10 L + R

Single-leg 4-way hop-hold ball,a 4 Cycles L + R

Squat, 10

Single-leg pelvic

Lateral jump and hold, 8 L + R

Prone-bridge hip extension, 10 L + R

Single-leg 180°, 10 L + R

Single tuck jump with soft landing, 10 L + R

Side-to-side tuck jumps, 10 L + R

Jump, jump, jump, vertical jump, 10 s

Lunge jumps, 10 s

Lateral hops, 10 s

Mattress jumps, 40 L + R

Lateral jumps, 10

Double-leg 90°, 8 L + R

Running, jump down 1-legged, jump, 8

Squat jumps, 10

Single-leg pelvic-bridge ball, 10 L + R

Single-leg 180°, 10 L + R

Lateral jumps, 10 s

Prone-bridge hip-opposed shoulder flexion, 10 L + R

Jump, jump, jump, vertical jump, 15 L+R

Double tuck jump, 8 L + R

Lateral hops with ball, 10 s

Running, jump down 1-legged, jump, 10

Broad jump, 10

Single-leg lateral hop-hold, 5 L + R

Layup,b 10

Scissor jumps, 8

Single-leg 90°, 8 L + R

Height jump,b 10

Note: Training sessions were held twice a week, with 10-min sets, 1-min rest between exercises. Abbreviations: L, left; R, right. a

Exercise on the mattress. b Sport-specific jumps for basketball, can be adjusted depending on the sport.

planes.19 Thirteen of these criteria evaluate the hip, knee, and ankle angles and distance between knees during the jump-landing movement. These kinematic variables were determined at initial contact and maximal knee flexion. Since a force plate was not used, initial contact was visually determined as the first frame in which the feet or toes touched the ground. Maximal flexion was determined as the frame where the athletes showed greatest knee-flexion angle. Range of motion (ROM) was calculated as the degree of movement that occurred in the joint. Other alignments such as distance between the knees during landing, valgus position, and alignment of the knees and toes were also examined. These remaining 22 criteria are scored with “present” (1) or “not present” (0). Positioning joints so that they are in a proper straight or parallel position is considered alignment. All variables of the JLS system are described in detail in previous research19 and are defined in the literature as being possible injury risk factors.8 Analysis show a high to moderate intrareliability

and interreliability (.90 ≥ r > .50; P < .05) of the different variables. The higher the score of the jump-landing technique measured with the JLS-system, the worse the jump-landing technique. The difference in the JLS system score after the intervention between the IG and CG (male and female) was determined. The cutoff values to indicate sufficient lower-extremity-flexion angles, based on literature,10,12,14 were used in the development of the JLS system. The averaged cutoff angles were determined as 20°, 20°, and 70° at initial contact for hip, knee, and ankle plantar flexion, respectively, and 40°, 50°, and 10° at maximal flexion for hip, knee, and ankle dorsiflexion. Lower degrees of ankle, knee, and hip flexion were determined as being riskier.

Sample Size The jump-landing prevention program was developed to prevent lower-extremity injuries. The power analysis

Intervention on Jump-Landing Technique  25

was therefore carried out for the main outcome variable, lower-extremity-injury incidence. We considered a difference of 50% in the incidence of lower-extremity injuries between the IG and CG after a follow-up of 1 season to be clinically relevant. The prevalence of lowerextremity injuries in basketball in Flanders is about 78% per season.1 Therefore, a total of 34 subjects per group are needed to detect the intended difference of 50% in the incidence of lower-extremity injuries, with a power of 90% and an alpha of 5%. Assuming a dropout rate of about 20%, a total of 82 athletes are needed to detect a potentially clinically relevant effect of the intervention. However, as teams serve as the unit of randomization, a cluster effect should be taken into account. Therefore, an intracluster correlation coefficient of 20% was considered, resulting in a total of 220 athletes from 24 teams that needed to be included at baseline.

and between preintervention and postintervention were determined using the Mann-Whitney U (P < .05).

Results Participants and Baseline Data A total of 116 subjects (63 in CG, 53 in IG) out of 243 athletes were measured both preintervention and postintervention (Figure 1). A total number of 51 dropouts (29 men, 22 women) in the CG and 76 (42 men, 34 women) in the IG are registered. Table 2 gives an overview of the baseline data for the IG, the CG, and the dropouts. No heterogeneity was observed for demographic data, between the IG and CG, or for the dropout compared with the participants.

Jump-Landing Technique

Statistical Analyses All jump-landing movements preintervention and postintervention were performed 3 times. The second jump landing was used to perform the statistical analysis. Previous data on the consistency of consecutive jump landings show that all variables had a high to good consistency (.98 ≥ r > .70) and a significant correlation (P < .05). The statistical analyses were performed on the male and female groups separately. To examine the homogeneity for all demographic data, an independent-samples t test (P < .05) was used. Lower-extremity flexion angles were defined as 0° being indicative of “neutral” anatomic position. Therefore, a negative ankle angle indicates dorsiflexion. Possible effects of the intervention program on the angles during the jump landing were determined by repeated-measures ANOVA (normally distributed data) or the Mann-Whitney U test (nonnormally distributed data) with a significance level set at .05. To determine the difference between IG and CG postintervention for the 22 nominal variables, a chi-square (χ2) analysis was performed. Differences between preintervention and postintervention were also analyzed with a χ2 analysis (P < .05). Eventually, we converted all criteria to nominal variables to determine the JLS system score. Differences in the scores of the JLS system between groups

Men.  The kinematic data in male athletes showed signif-

icant interaction effects of time × group and significant time effects preintervention to postintervention (Table 3). A significant interaction effect was found for kneeseparation distance. More male athletes normalized their knee-separation distance postintervention. However, at both measurements the average distance between knees was not significant between the measurements. In addition, a significant interaction effect was found for maximal hip flexion, maximal knee flexion, hip active ROM, and knee active ROM during landing. This interaction effect shows that the IG and CG changed in different ways, with the IG showing a significant improvement in technique. In addition, the IG significantly improved their maximal hip flexion (left +14.1° and right +11.5°; P < .05) and left-knee flexion (left +6.4°; P < .05) over time, whereas the CG showed no significant changes. In addition, a significant time effect for left- and right-hip flexion and knee flexion at initial contact was found. For these variables, both groups show similar significant positive changes preintervention to postintervention. Significant differences for alignment were also found. After the completion of the jump-landing prevention program, significantly fewer male athletes of the

Table 2  Demographic Data of the Subjects, Mean ± SD Group Intervention group Control group

Gender (n)

Control group dropouts

Length (cm)

Weight (kg)

Body-mass index (kg/cm2)

Male (27)

24.7 ± 4.9

189.1 ± 7.3

84.9 ± 10.3

23.72 ± 2.6

Female (26)

23.12 ± 5.8

173.7 ± 6.1

65.9 ± 9.7

21.78 ± 2.6

Male (31)

26.8 ± 5.4

189.7 ± 8.3

87.6 ± 9.4

24.34 ± 2.1

23 ± 3.9

174.3 ± 6.9

64.2 ± 8.0

21.1 ± 1.8

Female (32) Intervention group dropouts

Age (y)

Male (29)

25.7 ± 4.9

193.3 ± 8.6

96.3 ± 14.8

25.6 ± 2.5

Female (22)

21.3 ± 5.3

172.9 ± 6.3

62.3 ± 9.1

20.8 ± 2.5

Male (42)

25.1 ± 6.7

190 ± 9.7

88.0 ± 14.9

24.1 ± 2.6

Female (34)

20.2 ± 4.3

172.7 ± 6.1

63.1 ± 8.3

21.1 ± 2.0

Table 3  Lower-Extremity Angles (°) of Male and Female Intervention Group (IG) and Control Group (CG), Mean ± SD Preintervention

Postintervention

n

Left limb

Right limb

Left limb

Right limb

  knee-flexion IC

IG = 27

15.8† ± 6.5

16.4† ± 8.6

19.1† ± 7.1

18.9† ± 6.9



CG = 31

15.2† ± 6.7

13.9† ± 5.5

19.7† ± 8.6

17.8† ± 7.6

Male

  hip-flexion IC

IG = 27

12.6† ± 7.6

14.0† ± 6.7

16.2† ± 8.2

17.8† ± 8.8



CG = 31

12.7† ± 7.7

12.0† ± 8.9

15.3† ± 9.4

16.4† ± 9.5

  ankle-flexion IC

IG = 27

48.8 ± 9.3

43.8 ± 11.0

49.0 ± 10.8

46.6 ± 10.4



CG = 31

51.2 ± 10.5

47.0 ± 8.2

60.2 ± 10.9

50.2 ± 9.3

  maximal knee flexion*

IG = 27

57.0† ± 10.4

56.5 ± 12.2

63.4† ± 15.7

61.1 ± 14.3



CG = 31

57.9 ± 12.3

57.1 ± 11.3

60.6 ± 11.0

56.1 ± 11.1

  maximal hip flexion*

IG = 27

39.4† ± 19.2

44.0† ± 19.3

53.5† ± 24.7

55.5† ± 21.5



CG = 31

41.7 ± 16.1

42.2 ± 19.9

40.9 ± 18.7

41.9 ± 17.4

  maximal ankle flexion

IG = 27

–4.6 ± 6.3

–3.4 ± 7.6

–9.3 ± 5.7

–4.6 ± 7.3



CG = 31

–10.3 ± 9.0

–6.7 ± 8.7

–6.5 ± 5.7

–4.8 ± 5.9

  knee ROM*

IG = 27

41.2 ± 8.3

40.1 ± 12.2

44.3 ± 12.9

42.2 ± 12.5



CG = 31

42.7 ± 11.3

43.2 ± 9.8

40.9 ± 11.2

38.3 ± 8.4

  hip ROM*

IG = 27

26.7 ± 15.1

30.0 ± 15.6

37.3 ± 19.2

37.7 ± 17.6



CG = 31

29.0 ± 12.4

30.2 ± 16.0

25.6 ± 16.2

25.5 ± 16.7

  ankle ROM

IG = 27

44.1 ± 8.5

40.4 ± 11.1

39.7 ± 11.2

42.4 ± 9.3



CG = 31

40.9 ± 11.5

40.3 ± 10.8

53.7 ± 49.8

45.4 ± 9.5

Female   maximal knee-flexion IC*

IG = 26

20.8 ± 12.1

20.7 ± 8.0

23.4‡ ± 7.7

22.4‡ ± 9.0



CG = 32

20.8† ± 8.0

14.1† ± 9.4

11.3†‡ ± 6.4

9.6†‡ ± 8.9

  hip-flexion IC*

IG = 26

16.1 ± 10.5

18 ± 8.6

21.4‡ ± 10.3

23.4‡ ± 8.7



CG = 32

13.4 ± 9.9

12.7 ± 8.3

8.2‡ ± 6.3

8.3‡ ± 9.6

  ankle-flexion IC*

IG = 26

36.9‡ ± 10.9

30.3 ± 8.5

35.4 ± 12.1

30 ± 13.8



CG = 32

21.9†‡ ± 10.0

22.3† ± 9.9

38.6† ± 9.6

40.4† ± 10.0

  maximal knee flexion*

IG = 26

57.4 ± 13.2

53.1 ± 11.3

62.7‡ ± 9.9

58.1‡ ± 11.5



CG = 32

54.0† ± 10.7

53.7† ± 12.4

39.8†‡ ± 7.7

37.3†‡ ± 7.6

  maximal hip flexion*

IG = 26

37.0 ± 14.5

37.3 ± 9.9

46.3‡ ± 15.4

48.2‡ ± 14.7



CG = 32

31.5 ± 15.2

33.2 ± 12.6

23.7‡ ± 9.0

22.1‡ ± 8.9

  maximal ankle flexion*

IG = 26

–3.6 ± 6.4

–7.4 ± 4.8

–6 ± 6.8

–9.9 ± 6.2



CG = 32

–11.8 ± 5.1

–12.3 ± 7.0

–5.5 ± 6.1

–7.2 ± 7.2

  knee ROM *

IG = 26

36.6 ± 14.3

32.3 ± 10.4

39.3‡ ± 10.2

35.7 ± 13.7



CG = 32

33.2 ± 12.3

39.6† ± 11.9

28.5‡ ± 9.5

27.7† ± 11.1

  hip ROM*

IG = 26

20.9 ± 11.6

19.3 ± 8.5

24.9‡ ± 11.7

24.8‡ ± 15.8



CG = 32

18.1 ± 12.6

20.5 ± 10.8

15.5‡ ± 8.8

13.8‡ ± 12.2

IG = 26

40.4 ± 10.7

37.7 ± 10.2

41.3 ± 14.2

39.9 ± 12.3

CG = 32

33.7† ± 9.1

34.5† ± 10.1

44.1† ± 9.7

47.6† ± 10.7

  ankle ROM*

Abbreviations: IC, initial contact; ROM, range of motion. *Significant interaction effect of time and group (P < .05). †Significant difference (P < .05) between preintervention and postintervention. ‡Significant difference (P < .05) between CG and IG.

26

Intervention on Jump-Landing Technique  27

IG performed a jump landing with right genu valgus at takeoff. Women.  The kinematic data in female athletes also showed significant interaction effects of time × group, significant time effects, and significant differences between CG and IG. A significant interaction effect was found for hip, knee, and ankle flexion at initial contact (Table 3). Also, an interaction effect was found for maximal hip flexion, maximal knee flexion, maximal ankle flexion, hip active ROM, knee active ROM, and ankle active ROM during landing. This interaction effect indicates that the IG and CG changed in different ways, with the IG showing significantly better results. In addition, the CG significantly worsened their maximal knee flexion (left –14.2° and right –16.4°; P < .05) and left-knee flexion at initial contact (left –9.5°; P < .05) over time, whereas the IG showed no significant changes. Although no interaction effect was found, there was a significant time effect for knee-separation distance. Both groups normalized their knee-separation distance over time. Furthermore, at postintervention significant differences were detected between IG and CG for maximal hip flexion, maximal knee flexion, hip active ROM, knee active ROM, hip flexion, and knee flexion at initial contact. Side-to-side differences were found preintervention for maximal ankle flexion, whereas at postintervention, those side-to-side differences were not present. Also, in the female athletes influences on alignment were found. Significantly fewer female athletes of the IG performed a jump landing with left genu valgus during landing and genu valgus of both limbs during takeoff after the prevention program than preintervention.

JLS Score After the completion of the prevention program, male athletes of the IG significantly improved their JLS score

over time (from 17.4 ± 4.6 to 13.7 ± 3.2), whereas the male CG showed no improvement (from 14.9 ± 4.1 to 14.2 ± 3.8) (Figure 2). Although no significant improvement was found, JLS scores at postintervention were significantly different between female groups, with lower scores in their IG than their CG (IG 16.9 ± 4.4 and 15.3 ± 3.5 and CG 15.9 ± 4.4 and 16.9 ± 3.0, respectively, preintervention and postintervention).

Discussion The main purpose of this study was to determine the effect of a coach-supervised prevention program, originally established to prevent lower-extremity injuries, on the jump-landing technique. The effectiveness of the prevention program in reducing the incidence of lower-extremity injuries was already proven in a convergent study.3 That study showed that the risk of a lower-extremity injury was significantly lower in the IG than in athletes in the CG (hazard ratio = 0.40 [95% CI: 0.16–0.99]).25 These results show that the injury-prevention program was effective in preventing injuries. Moreover, literature suggests that there is a relationship between injuries and jump-landing technique.9,10 Therefore we wanted to investigate the influence of the prevention program on jump-landing technique measured by the JLS system. Interaction effects were found for maximal hip and knee flexion and hip and knee active ROM for the male and female athletes. Furthermore, interaction effects were found for ankle active ROM and for hip, knee, and ankle flexion at initial contact in female athletes. Overall, athletes in the IG landed with a significantly less-erect position than those in the CG. Blackburn and Padua29 found that athletes who introduced more hip flexion into their jump-landing technique simultaneously increased maximal knee flexion during landing. Furthermore, limited hip-flexion motion in combination with reduced knee

Figure 2 — The mean jump-landing-scoring (JLS) system score of the intervention group (IG) and control group (CG) at preintervention and postintervention. *Significant difference between IG and CG at P < .05.

28  Aerts et al

active motion reduces the ability of the lower extremity to absorb the impact forces9,30 and increases the risk of lower-extremity injuries such as anterior cruciate ligament injuries10 or patellar tendinopathy.31 In addition, our results are in agreement with the findings of Myer et al,23 who found that plyometric training and specific balance training have a positive influence in lower-extremity flexion, suggesting that our prevention program can alter lower-extremity-flexion movement and thus prevent lower-extremity injuries. Furthermore, literature32 states that athletes who performed a jump landing with limited lower-extremity flexion, increased knee-valgus angles, increased kneeadductor moments, increased vastus lateralis activity, and decreased energy absorption at the knee and hip compared with athletes who perform a jump landing with larger flexion angles have an increased risk of lower-extremity injury, suggesting that both frontal- and sagittal-plane lower-extremity biomechanics are important. This means that intervention programs should focus not only on valgus position during the jump-landing movement but also on sagittal lower-extremity biomechanics. As Noyes et al33 mentioned before, landing in a varus or valgus position is a less-stable position for the knee and is related to increased injury occurrence. This proves the importance of performing a jump-landing movement with sufficient active lower-extremity flexion and lowerextremity alignment. Although no significant interaction effect was found between the IG and CG regarding valgus position, our results show that significantly fewer athletes in the IG performed a jump landing in valgus position postintervention, probably due to the improvement in the lower-extremity sagittal-plane kinematics. Literature34,35 also suggests an important influence of knee-separation distance on knee-valgus position. We detected a significant interaction effect for kneeseparation distance in male and female athletes. However, the CG also normalized their knee-separation distance postintervention. No other significant differences were found regarding alignments. The male IG showed significant improvement of the JLS score preintervention versus postintervention. Although no significant improvement over time was found, JLS scores at postintervention were significantly different between female IG and CG (P < .05). A possible explanation is that the statistical power is not sufficient to detect significant differences in the female athletes. Post hoc analysis showed that 31 athletes were needed per group to detect a significant difference in the JLS score. This criterion was not met in the female population. Furthermore, different studies show that kinematic differences exist between female and male athletes for knee valgus and hip and knee flexion during different high-impact movements.16,36 Male athletes seem to demonstrate less excessive malalignment of the lower extremity and are therefore more likely to have improved their JLS score. In addition, our results showed that the female CG JLS score declined at postintervention. Barendrecht et al37 recommended a neuromuscular training program of

20 minutes twice a week for 10 weeks to improve landing kinematics and single-leg stability in both male and female handball players. Players with higher initial valgus angles would benefit most from neuromuscular training. Perhaps female athletes in the CG had not received adequate neuromuscular training and therefore their JLS score was lower postintervention. The cutoff values to indicate sufficient lower-extremity-flexion angles, based on literature,10,12,14 probably need revision once more studies are performed on this topic. Most studies have only determined the difference between injured and uninjured athletes instead of determining the predictive value. However, several alterations in lower-extremity angles and alignments did manifest changes in the JLS score. Not only is the attained score important, but also whether several separate variables could be altered with the prevention program. A strength of our study was that the CG was unaware of an existing IG and vice versa, so the Hawthorne effect was limited.27 Another strength is that our prevention program was previously proven to be effective in the prevention of lower-extremity injuries. Furthermore, it was easily implementable and only basic equipment was needed to perform the exercises that the coaches found to be important.25 A limitation was the high dropout rate (IG n = 43, CG n = 63) due to the fact that coaches did not follow the exercise program because of lack of interest or time and absence of athletes during postintervention measurements. Nonetheless, the demographic data of the dropouts and the participating athletes were homogeneous. More detailed information on the data of the applicability of the jump-landing prevention program were reported in 2013.25 Another limitation of this study was that, as mentioned before, an improvement in the JLS score was limited due to ceiling effects of different variables, meaning that several individuals had no room for improvement, and therefore no significant changes could be detected. Still, most athletes who were able to improve their results did show an improvement. However, the JLS system is capable of detecting differences in variables such as knee flexion, hip flexion, and sagittal shoulder–knee alignment, which are identified as risk factors in literature.8 The goal of our JLS system was to be practical to use and implement by coaches in on-field situations. Therefore, in the development of the JLS system we used biomechanical parameters and converted them to well- and predefined variables clearly understandable for coaches (translated to nominal variables). Future research can focus on adapting the JLS system to include solely the predictive risk factors. Frontal-plane knee-angle projections probably comprise several 3-dimensional lower-limb joint rotational components. McLean et al38 reported significant correlations between peak 2-dimensional and 3-dimensional frontal-plane knee angles during full-speed cutting. Also, Mizner et al39 found that the 2-dimensional analysis of knee-separation distance had favorable rater reliability and accounted for a high

Intervention on Jump-Landing Technique  29

variance of 3-dimensional knee-abduction angle and knee-abduction moment, which are determined as risk factors for ACL injuries.10

Conclusion When summarizing our results, we conclude that several variables such as knee valgus and lower-extremity flexion, which are identified as risk factors for lower-extremity injuries, can be influenced by our prevention program. Jump-landing training not only decreases the potential biomechanical risk factors for lower-extremity injury but also can provide additive performance-enhancement effects.40 Our previous study25 showed that the prevention program had a positive influence on injury occurrence, suggesting a positive relationship between jump-landing technique and injury prevention. The prevention program can thus help improve lower-extremity kinematics and alignment during a jump-landing movement. Coaches should be able to evaluate the jump-landing technique of their athletes. More specifically, they should be aware of the consequences of insufficient lower-extremity flexion and malalignment during jump landing and should instruct their athletes correctly. The JLS system can help in evaluating these variables. Financial Disclosure and Conflict of Interest We affirm that we have no financial affiliation or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript.

Acknowledgments This study was financially supported by the Flemish Government through the establishment of the policy Research Center Sports, Youth and Culture. The authors thank all the athletes and persons responsible for a successful participation on a voluntary basis. The study protocol was accepted by the local ethical committee of the Vrije Universiteit Brussel (B.U.N. B14320071963), and a trial registration number was requested (NTR2560).

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The effect of a 3-month prevention program on the jump-landing technique in basketball: a randomized controlled trial.

In jump-landing sports, the injury mechanism that most frequently results in an injury is the jump-landing movement. Influencing the movement patterns...
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