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Study design
The present study was a quasi-experimental design due to the presence of the control group and also an intervention in the experimental group.
Participants
The population included 30 female basketball players (n = 30, age = 15.50 ± 1.52 years, height = 1.62 ± 0.06 cm, weight = 55.15 ± 9.65 kg, BMI = 20.69 ± 2.80 kg/m2, leg length = 85.46 ± 3.69 cm, sports history = 3.73 ± 1.56 years) with DKV defects. The sample size was determined to be 30 by purposive sampling using G*Power software with a desired power of 0.50, an alpha of 0.05, and an effect size of 0.75. This effect size was comparable to previous research reporting changes in landing mechanics after neuromuscular training with dual cognitive tasks [20].
Randomization.
Randomization was performed by an independent investigator unfamiliar with the testing protocol using a random allocation rule. The letters A and B were identified as markers for random groups assignment and were placed in sealed opaque envelopes in a box. Another researcher opened envelopes and proceeded with training according to the group assignment. These letters were numbered randomly selected and placed one after the other. Thus, the subjects were divided into two groups A (experimental = 15) and B (control = 15). Group allocation was concealed using an opaque envelope until after athletes had been enrolled in the study to minimize potential bias.
Furthermore, the present study was a single-blind study in which only the researchers knew which intervention the participants were receiving and the subjects did not know which study group they were in until the study was over. The pre-test lasted for 1 week. To prevent injury, the subjects were asked to perform an initial warm-up before doing the pre-test. After the pre-test, the experimental group underwent STOP-X training, in addition to their usual training. In that time, the subjects of the control group performed their usual exercises. After 8 weeks, the post-test was conducted, which lasted for 1 week. Afterwards, the collected data were analyzed.
Eligibility criteria.
The inclusion criteria consisted of 14- to 19-year-old females with a knee valgus angle greater than 12° during single-leg landing (SLL) [21, 22], a minimum of 3 years of training experience, a regular training routine (at least three training sessions per week), no history of lower extremity injuries in the past six months leading to functional or structural limitations or lower extremity surgery leading to changes in normal alignment, and the absence of spine-related and upper extremity musculoskeletal disorders. Otherwise, the exclusion criteria consisted of noncooperative subjects in the pretest or posttest, failure to complete the training program for any reason, absence of more than three exercise sessions or two consecutive sessions [23], pain or injury during exercise, and unwillingness to continue cooperation. This research was performed under controlled and identical conditions for subjects in a safe environment at the Qazvin Basketball Club. Once selected, the participants signed an informed written consent form, including explanations about the steps, objectives, and research participation conditions. Ethical considerations were followed in this research, and the code of ethics (ID IR.GUILAN.REC.1402.015) was obtained from the Ethics Committee in Biomedical Research (ETHICS), Guilan University. This study adhered to CONSORT guidelines for randomized controlled trials and had been registered in the Iranian Registry of Clinical Trials (ID: IRCT20231230060574N1, on 04/01/2024). subjects’ allocation and dropouts were remarked at the study flowchart (Fig. 1).
Outcome measurement
Single-leg landing test.
This study screened and determined the DKV using the SLL test, which demonstrated a reliability of 0.87 [24]. To perform this test, the subjects dropped directly down off a 30-cm-high box onto a mark 30 cm from the box, made landfall on the dominant leg and held the position. The participants then stood in a balanced position (stance) near the edge of the box so that the dominant leg was suspended (heel in contact with the edge of the box). A digital video camera (with external memory) was placed on a tripod at the height of the subject’s knee at a distance of 230 cm from the box in the frontal view. Three successful trials were recorded for each subject. The mean angles of the three trials above were used in the final analysis. The knee valgus angle of the dominant leg was then measured using the Kinovea software package (reliability = 0.98) [25]. A frame-by-frame analysis of the video images demonstrated that the complete landing image is the frame where the subject is at the lowest height (i.e., maximum knee flexion). The angle subtended between the lines formed between the markers at the ASIS and middle of the tibiofemoral joint and that formed from the markers on the middle of the tibiofemoral joint to the middle of the ankle mortise was recorded as the valgus angle of the knees [21, 26]. The identified markers were located in three areas: the ASIS of the landing leg, the center of the patella, and the center of the ankle mortise. The normal knee valgus angle was in the range of 5–12° for females during the SLL test [21, 22]. Females with knee valgus angles greater than 12° during SLL were included in this study as those with DKV. Harrington et al. suggested that 2D video kinematics have a reasonable association with what is being measured with 3D motion capture [24].
Static balance test.
Static balance was evaluated using the Bass–Stick test, which records how long a person can stand for 60 s on a 2.5-cm wooden block without touching the ground. This test was performed three times on the dominant leg, and the best result was considered the static balance test score [27]. Test-retest reliability was reported to be 0.91 [28].
Dynamic balance test.
To perform the dynamic balance test, the true leg length (from the ASIS to the distal portion of the medial malleolus) was measured to normalize the data and compare the subjects. Additionally, the dominant leg was evaluated using the ball-kicking test. This research employed the Y-balance test (YBT) to evaluate dynamic balance. Y-Balance Test Kit was also used to evaluate this test. Before the test, each subject performed the test three times as a practice to minimize the learning effect. After that, the subject rested and performed the test three times with dominant leg. The participants were asked to stand in the center of their directions, place themselves on the dominant leg, reach the other leg, return to the normal position on both legs, and maintain their position for 10–15 s before the next trial. All trials in a single direction had to be completed sequentially clockwise or counterclockwise before proceeding in the next direction. The subjects were asked to touch the farthest possible point in any given direction with their toe. The reach distance was defined as the distance from the contact point to the center in centimeters. The difference between the average balance scores (YBT) in each direction was measured separately using Eq. (1). The validity of the YBT was reported to be 0.85–0.93 [29]. Also, there was moderate to high quality evidence demonstrating that the YBT is a reliable dynamic neuromuscular control test with Intra-rater reliability ranged from 0.85 to 0.91 [30]. The normalized average of three repetitions was recorded as the score. The effort was repeated in the event of the following situations: hands being separated from the hip, using the reaching leg to bear weight, moving the supporting leg and losing balance. To calculate the total score of the dynamic balance test, the measurements of all three directions were added together and divided by three times the length of the dominant leg.
$$ \mathbf{S}\mathbf{c}\mathbf{o}\mathbf{r}\mathbf{e}=\frac{\mathbf{r}\mathbf{e}\mathbf{a}\mathbf{c}\mathbf{h} \mathbf{d}\mathbf{i}\mathbf{s}\mathbf{t}\mathbf{a}\mathbf{n}\mathbf{c}\mathbf{e} }{\mathbf{l}\mathbf{e}\mathbf{g} \mathbf{l}\mathbf{e}\mathbf{n}\mathbf{g}\mathbf{t}\mathbf{h}}\times 100$$
Intervention
Knee injury prevention training program (STOP-X program)
Based on the results of medical research, STOP-X has been developed as a prevention concept that can reduce the risk of serious knee joint injuries, which includes programs that can be integrated into normal training. The prevention strategy consisted of several elements, including teaching injury mechanisms, correcting dangerous movement patterns, balance exercises, neuromuscular training for muscular coordination, and hip stabilization exercises [31]. The STOP-X program consisted of running, balance training, a jump-landing pattern, and strength training for 25–40 min for eight weeks (three times per week). Although the program can be used integrally for warm-up, athletes with DKV can run it to correct their defects and reduce the incidence of knee injuries by up to 27% and ACL injuries by up to 51% [11]. The program started with simple exercises, and the difficulty level of individual exercises increased over time. The STOP-X program comprises a variety of proven injury recovery programs, including the Henning program, the Vermont Alpine Knee injury program, the FIFA 11 + program, the Monica Santa Injury program, the Oslo Handball injury program, and the aerial program from German handball injury [31, 32]. The aforementioned training program is presented in Table 1. After the variables were determined during the pretest, the subjects in the experimental group performed the STOP-X program for eight weeks as warm-ups at the beginning of the basketball exercises. In contrast, the control group simply performed routine warm-up, including running, stretching, warm-up with a ball at the beginning of the basketball exercises with the same time schedule. Another point is that the routine warm-up program in the control group lacked strength, balance, stability and performance exercises to have the ability to influence the landing mechanics of the athletes, while the STOP-X training include these items.
Statistical analysis
To assess the normality of data distribution and homogeneity of variances, Shapiro-Wilk and Levene’s tests were used, respectively. Descriptive statistics were calculated for all variables, and mean, and standard deviation (SD) were reported. Independent samples t-test was applied to compare the demographic characteristics of the two groups. Then, according to the research design, Two-factor ANOVA test 2 (group: experimental, control) × 2 (time: pre-test, post-test) with a group x condition interaction was used to analyze the within and between group evaluation over the eight-week STOP-X training. If a significant interaction effect was found between factors, post hoc analyses (paired t-test) with Bonferroni adjustment for pairwise comparisons were applied. Within-group factor (pre-test to post-test) as the main effect of time and between-group as the main effect of the group were considered. Percentage changes from the pre-test to the post-test were calculated. Effect sizes (ES) using partial eta squared were calculated to increase the analysis power. Effect sizes were classified as small (0.01), moderate (0.06), and large (0.14) [33]. A modified intention to treat analysis based on the complete case method was used. In this method, since one person was randomly removed from each control and experimental group, they were excluded from the study. The analysis was performed only on those who completed the pre-test and post-test. Findings were analyzed at a significance level of 95%, with a statistical significance of (p < 0.05), and performed using IBM SPSS software (SPSS, version 26, Chicago; IL).
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