Normalized Knee Separation Distance Research Articles

CHANGE IN KNEE SEPARATION DISTANCE IN ADOLESCENT ATHLETES AFTER A 6-WEEK NEUROMUSCULAR TRAINING PROGRAM

Background:Existing neuromuscular injury prevention programs have relied principally on lower extremity strengthening, agility, cutting and landing technique to improve jump landing mechanics in order to prevent non-contact knee ligament injuries.Purpose:To determine whether a 6-week neuromuscular training program emphasizing core (back & hip) strengthening and dynamic balance exercises can significantly improve normalized knee separation distance (nKSD) during a standard counter-movement jump landing maneuver.Methods:Fourteen adolescent athletes (11 boys, 3 girls, ages 12-15) volunteered to undergo a 2 day/week, 6-week off-season training program. On the first day of training, the athletes underwent assessments that included 2 trials of a counter-movement jump from a 40cm platform. The tests were recorded using a video camera in the frontal plane. Using Dartfish motion analysis software, knee separation distance (KSD) was measured as the distance (cm) between the femoral condyles at the lowest point of the jump landing, and intertrochanteric distance (ITD) as the distance (cm) between the femoral trochanters. Normalized knee separation distance was computed as nKSD = KSD/ITD. The training program focused on three progressions; increasing difficulty of core strengthening exercises, balance exercises, and agility drills. One-hour training sessions were subdivided as follows; 5 min dynamic warm-up, 10 min stretching, 10 min body weight core exercises, 15 min balancing exercises, 10 min dumbbell core exercises, 15 minute agility drills, 5 min of rest/hydration breaks. The athletes repeated the counter-movement jump test at the end of the 6 weeks.Results:There was a significant improvement (t = 2.740, p = 0.017) in nKSD between post-test (0.789 + 0.372) and pre-test (0.683 + 0.323)Conclusion:A 6-week neuromuscular training program focused on core strengthening and balance significantly improved jump landing mechanics which may reduce the risk of knee ligament injury.

Intra- and interrater reliability of subjective assessment of the drop vertical jump and tuck jump in youth athletes

ObjectivesTo investigate intra- and interrater reliability of the subjective assessments of filmed DVJ and TJA in youth male and female soccer players and to compare subjective assessment of the DVJ with two-dimensional movement analysis. DesignCross-sectional study. Participants115 soccer players (66 boys, 49 girls) mean age 14 ± 1 (range 13–16) years. Main outcome measuresKnee control during landing phase of DVJ was assessed using a 3-graded scoring scale. TJA was assessed according to ten criteria using a dichotomous grading scale. Subjective assessment of DVJ was compared with calculation of normalized knee separation distance (NKSD). ResultsIntrarater reliability for DVJ was substantial to almost perfect (kappa 0.72 rater 1; 0.85 rater 2). Interrater reliability was substantial to almost perfect (kappa from 0.68 to 0.83). The TJA total score intrarater reliability was ICC 0.59 for rater 1 and 0.90 for rater 2. Interrater reliability ranged from ICC 0.51 to 0.60. There were between-group differences in mean NKSD during DVJ for players rated as 0, 1 and 2, but within-group variability was large. ConclusionAssessment of DVJ and TJA in youth athletes was rater dependent. Players with subjectively assessed reduced or poor knee control had smaller normalized knee separation distance in DVJ.

Effectiveness of a home-based re-injury prevention program on motor control, return to sport and recurrence rates after anterior cruciate ligament reconstruction: study protocol for a multicenter, single-blind, randomized controlled trial (PReP)

BackgroundAlthough anterior cruciate ligament (ACL) tear-prevention programs may be effective in the (secondary) prevention of a subsequent ACL injury, little is known, yet, on their effectiveness and feasibility. This study assesses the effects and implementation capacity of a secondary preventive motor-control training (the Stop-X program) after ACL reconstruction.Methods and designA multicenter, single-blind, randomized controlled, prospective, superiority, two-arm design is adopted. Subsequent patients (18–35 years) with primary arthroscopic unilateral ACL reconstruction with autologous hamstring graft are enrolled. Postoperative guideline rehabilitation plus Classic follow-up treatment and guideline rehabilitation plus the Stop-X intervention will be compared. The onset of the Stop-X program as part of the postoperative follow-up treatment is individualized and function based. The participants must be released for the training components. The endpoint is the unrestricted return to sport (RTS) decision. Before (where applicable) reconstruction and after the clearance for the intervention (aimed at 4–8 months post surgery) until the unrestricted RTS decision (but at least until 12 months post surgery), all outcomes will be assessed once a month. Each participant is consequently measured at least five times to a maximum of 12 times. Twelve, 18 and 24 months after the surgery, follow-up-measurements and recurrence monitoring will follow. The primary outcome assessement (normalized knee-separation distance at the Drop Jump Screening Test (DJST)) is followed by the functional secondary outcomes assessements. The latter consist of quality assessments during simple (combined) balance side, balance front and single-leg hops for distance. All hop/jump tests are self-administered and filmed from the frontal view (3-m distance). All videos are transferred using safe big content transfer and subsequently (and blinded) expertly video-rated. Secondary outcomes are questionnaires on patient-reported knee function, kinesiophobia, RTS after ACL injury and training/therapy volume (frequency – intensity – type and time). All questionnaires are completed online using the participants’ pseudonym only.Group allocation is executed randomly. The training intervention (Stop-X arm) consists of self-administered home-based exercises. The exercises are step-wise graduated and follow wound healing and functional restoration criteria. The training frequency for both arms is scheduled to be three times per week, each time for a 30 min duration. The program follows current (secondary) prevention guidelines.Repeated measurements gain-score analyses using analyses of (co-)variance are performed for all outcomes.Trial registrationGerman Clinical Trials Register, identification number DRKS00015313. Registered on 1 October 2018.

Reliability of a field-based drop vertical jump screening test for ACL injury risk assessment

Objectives: There is an epidemic of anterior cruciate ligament (ACL) injuries in youth athletes. Poor neuromuscular control is an easily modifiable risk factor for ACL injury, and can be screened for by observing dynamic knee valgus on landing in a drop vertical jump test. This study aims to validate a simple, clinically useful population-based screening test to identify at-risk athletes prior to participation in organized sports. We hypothesized that both physicians and allied health professionals would be accurate in subjectively assessing injury risk in real-time field and office conditions without motion analysis data and would be in agreement with each other. Methods: We evaluated the inter-rater reliability of risk assessment by various observer groups, including physicians and allied health professionals, commonly involved in the care of youth athletes. Fifteen athletes age 11–17 were filmed performing a drop vertical jump test. These videos were viewed by 242 observers including orthopaedic surgeons, orthopaedic residents/fellows, coaches, athletic trainers (ATCs), and physical therapists (PTs), with the observer asked to subjectively estimate the risk level of each jumper. Objective injury risk was calculated using normalized knee separation distance (measured using Dartfish, Alpharetta, GA), based on previously published studies. Risk assessments by observers were compared to each other to determine inter-rater reliability, and to the objectively calculated risk level to determine sensitivity and specificity. Seventy one observers repeated the test at a minimum of 6 weeks later to determine intra-rater reliability. Results: Between groups, the inter-rater reliability was high, κ = 0.92 (95% CI 0.829–0.969, p < 0.05), indicating that no single group gave better (or worse) assessments, including comparisons between physicians and allied health professionals. With a screening cutoff isolated to subjects identified by observers as “high risk”, the sensitivity was 63.06% and specificity 82.81%. Reducing the screening cutoff to also include jumpers identified as “medium risk” increased sensitivity to 95.04% and decreased the specificity to 46.07%. Intra-rater reliability was moderate, κ = 0.55 (95% CI 0.49–0.61, p < 0.05), indicating that individual observers made reproducible risk assessments. Conclusions: This study supports the use of a simple, field-based observational drop vertical jump screening test to identify athletes at risk for ACL injury. Our study shows good inter- and intra-rater reliability and high sensitivity and suggests that screening can be performed without significant training by physicians as well as allied health professionals, including: coaches, athletic trainers and physical therapists. Identification of these high-risk athletes may play a role in enrollment in appropriate preventative neuromuscular training programs, which have been shown to decrease the incidence of ACL injuries in this population.

Physician And Non-physician Inter- And Intra-observer Reliability Of A Field-based Drop Vertical Jump Screening Test For ACL Injury Risk

Objectives:There is an epidemic of ACL injuries in pediatric and adolescent athletes. Poor neuromuscular control is an easily modifiable risk factor for ACL injury, and can be screened for by observing dynamic knee valgus on landing in a drop-vertical jump test. This study aims to validate a simple, clinically useful population-based screening test to identify at-risk athletes prior to participation in organized sports. We evaluated the inter- and intra-rater reliability of risk assessment by various observer groups, including physicians and non-physicians, commonly involved in the care of youth athletes.Methods:The screening involves observers watching a simple drop vertical jump in sports field conditions, without the use of additional analytic equipment. 15 athletes age 9-17 were filmed performing a drop vertical jump test. These videos were viewed by 242 observers including orthopaedic surgeons, residents/fellows, coaches, athletic trainers (ATC), and physical therapists (PT), with the observer asked to subjectively estimate the risk level of each jumper. Analytical objective injury risk was calculated using normalized knee separation distance (measured using Dartfish, Alpharetta, GA), based on previously published studies. Risk assessments by observers were compared to each other to determine inter-rater reliability and to the objectively calculated risk level to determine sensitivity and specificity. 71 observers repeated the test at a minimum of 6 weeks later to determine intra-rater reliability.Results:Overall, between groups (ATCs, attending physicians, coaches, residents/fellows, and PTs), the inter-rater reliability was high, κ = 0.92 (95% CI 0.829-0.969, p<0.05), indicating that no one group gave better (or worse) answers, including comparisons between physicians and non-physicians. With a screening cutoff of only jumpers identified by observers as “high risk”, the sensitivity was 63.06% and specificity 82.81%. Reducing the screening cutoff to also include jumpers identified as “medium risk” increased sensitivity to 95.04% and decreased the specificity to 46.07%. Intra-rater reliability was substantial, κ = 0.55 (95% CI 0.49-0.61, p<0.05), indicating that individual observers made reproducible risk assessments.Conclusion:This study supports the use of a simple, field-based observational drop vertical jump screening test to identify athletes at higher risk for ACL injury. Among those who could potentially be involved in this screening process, our study shows good inter- and intra-rater reliability and high sensitivity, and can be performed without significant training by coaches and athletic trainers in addition to healthcare professionals. Identification of these high-risk athletes may play a role in enrollment in appropriate preventative neuromuscular training programs, which have been shown to decrease the incidence of ACL injuries in this population.

Real-time feedback during drop landing training improves subsequent frontal and sagittal plane knee kinematics

BackgroundAlthough neuromuscular training featuring visual feedback may benefit modification of anterior cruciate ligament injury-risk linked knee kinematics, wide-spread clinical intervention has been limited to date. This study evaluated the effects of a Microsoft Kinect-based feedback system for modification of drop vertical jump knee kinematics traditionally consistent with predisposition to non-contact anterior cruciate ligament injury in female athletes. We hypothesized that a four-week feedback training protocol would increase peak knee flexion angle and frontal plane valgus-correlated knee separation distance during drop jump landing performance. MethodsTwenty-four female athletes were randomly divided equally into control or Kinect-based feedback groups. Subjects were pre-screened for peak knee flexion angle and minimum knee separation distance during drop landing and later performed twenty 31cm drop landings three days per week for four weeks. The feedback group received Kinect-based visual feedback, while controls did not. Kinematics were re-assessed immediately following the end of the training period. FindingsThe feedback group increased peak knee flexion and experienced a greater improvement in peak knee flexion. The feedback group improved normalized knee separation distance with greater improvement in post-training peak knee separation distance as compared with controls. InterpretationKinect-based feedback training significantly improved drop vertical jump knee kinematics associated with non-contact anterior cruciate ligament injury. The Kinect-based feedback approach demonstrates promise for mitigating non-contact anterior cruciate ligament injury predisposing knee biomechanics in female athletes within the clinical environment.

A Training Program to Improve Neuromuscular and Performance Indices in Female High School Soccer Players

The purpose of this study was to determine if a sports-specific anterior cruciate ligament injury prevention training program could improve neuromuscular and performance indices in female high school soccer players. We combined components from a published knee ligament intervention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic fitness. We hypothesized that this program would significantly improve neuromuscular and athletic performance indices in high school female soccer players. The supervised 6-week program was done 3 d·wk(-1) for 90-120 minutes per session on the soccer fields and weight room facilities in area high schools. In phase 1, 62 athletes underwent a video drop-jump test, t-test, 2 vertical jump tests, and a 37-m sprint test before and upon completion of the training program. In phase 2, 62 other athletes underwent a multistage fitness test before and after training. There were significant improvements in the mean absolute knee separation distance (p < 0.0001), mean absolute ankle separation distance (p < 0.0001), and mean normalized knee separation distance (p < 0.0001) on the drop-jump, indicating a more neutral lower limb alignment on landing. Significant improvements were found in the t-test (p < 0.0001), estimated maximal aerobic power (p < 0.0001), 37-m sprint test (p = 0.02), and in the 2-step approach vertical jump test (p = 0.04). This is the first study we are aware of that demonstrated the effectiveness of a knee ligament injury prevention training program in improving athletic performance indices in high school female soccer players. Future studies will determine if these findings improve athlete compliance and team participation in knee ligament injury intervention training.

A Training Program to Improve Neuromuscular and Performance Indices in Female High School Basketball Players

The purpose of this study was to determine if a sports-specific training program could improve neuromuscular and performance indices in female high school basketball players. We combined components from a published anterior cruciate ligament injury prevention program for jump and strength training with other exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. We hypothesized that this sports-specific training program would lead to significant improvements in neuromuscular and performance indices in high school female basketball players. Fifty-seven female athletes aged 14-17 years participated in the supervised 6-week program, 3 d·wk(-1) for approximately 90-120 minutes per session. The program was conducted on the basketball court and in weight room facilities in high schools. The athletes underwent a video drop-jump test, multistage fitness test, vertical jump test, and an 18-m sprint test before and upon completion of the training program. All the subjects attended at least 14 training sessions. After training, a significant increase was found in the mean estimated VO2max (p < 0.001), with 89% of the athletes improving this score. In the drop-jump video test, significant increases were found in the mean absolute knee separation distance (p < 0.0001) and in the mean normalized knee separation distance (p < 0.0001), indicating a more neutral lower limb alignment on landing. A significant improvement was found in the vertical jump test (p < 0.0001); however, the effect size was small (0.09). No improvement was noted in the sprint test. This program significantly improved lower limb alignment on a drop-jump test and estimated maximal aerobic power and may be implemented preseason or off-season in high school female basketball players.

Knee Separation Distance and Lower Extremity Kinematics During a Drop Land: Implications for Clinical Screening

Excessive knee valgus during dynamic tasks is thought to contribute to lower extremity overuse and traumatic injuries. Clinically, assessments of frontal-plane knee motion typically include measures of the distance between the knees during landing. However, it is not clear how this clinical assessment relates to knee-abduction angle or how it is influenced by the position of the lower extremities in the transverse and frontal planes. To determine whether normalized knee separation distance (NKSD) is a predictor of knee-abduction angles and to assess the influence of lower extremity transverse-plane and frontal-plane angles on NKSD during a drop land. Cross-sectional study. Motion analysis laboratory. Twenty-five healthy female athletes. The frontal-plane distance between the 2-dimensional coordinates of markers over the greater trochanters (intertrochanteric distance), lateral femoral epicondyles (knee separation distance), and lateral malleoli (stance width) bilaterally was calculated during a drop land. The knee separation distance was normalized by intertrochanteric distance (NKSD). Concurrently, 3-dimensional lower extremity transverse-plane and frontal-plane kinematics were obtained. We assessed NKSD, stance width, and bilateral average knee and hip transverse plane and frontal-plane angles and ankle frontal-plane angles. Linear regression was used to determine the association between NKSD and bilateral average knee frontal-plane angles. Stepwise multiple regression was used to identify the best predictors of NKSD during the drop land. After we controlled for stance width, NKSD explained 52% of the variance in the knee frontal-plane angle. When we took lower extremity kinematics into account, after controlling for stance width, the average hip frontal-plane angle was the best predictor of NKSD, explaining 97% of the variance. Although NKSD is a predictor of knee-abduction angle, frontal-plane hip angle and stance width are strongly related to NKSD. Caution must be taken when interpreting NKSD as knee abduction.

A Training Program to Improve Neuromuscular Indices in Female High School Volleyball Players

The purpose of this study was to determine if a sports-specific training program could improve neuromuscular indices in female high school volleyball players. We combined components from a previously published knee ligament injury prevention intervention program for jump and strength training with additional exercises and drills to improve speed, agility, overall strength, and aerobic conditioning. We hypothesized that this sports-specific training program would lead to significant improvements in neuromuscular indices in high school female volleyball players. Thirty-four athletes (age 14.5 years ± 1.0) participated in the supervised 6-week program, 3 d·wk(-1) for approximately 90-120 minutes per session. The program was conducted on the school's volleyball court and weight room facilities. The athletes underwent a video drop-jump test, multistage fitness test, vertical jump test, and sit-up test before and after training. A significant increase was found in the mean VO2max score (p < 0.001), where 73% of the athletes improved this score. A significant improvement was found in the sit-up test (p = 0.03) and in the vertical jump test (p = 0.05), where 68% of the athletes increased their scores. In the drop-jump video test, significant increases were found in both the mean absolute knee separation distance (p = 0.002) and in the mean normalized knee separation distance (p = 0.04), indicating improved lower limb alignment on landing. No athlete sustained an injury or developed an overuse syndrome during training. This program significantly improved lower limb alignment on a drop-jump test, abdominal strength, estimated maximal aerobic power, and vertical jump height and may be implemented in high school female volleyball programs.

Benefits of Neuromuscular Training Program for Knee Injury Prevention and Perfromance Enhancement in High School Female Basketball Players

PURPOSE: Various training programs have been developed for female athletes to improve neuromuscular deficiencies in order to reduce the incidence of knee ligament injuries. We developed a program for high school female basketball players designed to improve both lower limb alignment on landing from a drop-jump, as well as speed, agility and cardiovascular capacity. Thus, the purpose of this study was to investigate the effectiveness of a comprehensive neuromuscular training program on landing mechanics and selected sports-specific performance parameters in high school female basketball players. METHODS: Fifty-nine female high school basketball players aged 13 to 17 participated in a supervised 6-week neuromuscular training program. A previously published program was used, with the addition of exercises/drills to improve speed, agility, strength, and cardiovascular capacity. A battery of tests were administered before and after the training program including a video-recorded drop-jump test, multi-stage fitness test, vertical jump, and 20-yard dash test. RESULTS: Athlete compliance with training was high, as all participants attended at least 15 of the 18 training sessions. The aerobic capacity (V̇o2max) showed significant increase (34.1 ± 4.3 pre-train and 39.6 ± 7.1 ml/kg/min post-train, p < .0001), with 53 athletes demonstrating improved scores. Improvements were also found in the drop-jump test for the normalized knee separation distance (42.7 ± 16.5 pre-train and 76.0 ± 19.6 post-train, p < .0001) and the mean absolute separation distance (cm) of knees on landing (17.7 ± 7.2 pre-train and 31.7 ± 10.5 post-train, p < .0001). Further, the vertical jump performance improved from pre- to post-training (14.1 ± 2.7 pre-train and 16 ± 3.7 inches post-train, p < .0001) as well as the 20-yard dash times (3.53 ± .3 pre-train and 3.45 ± .45 post-train, p = .0374). Before training, 51 of the athletes demonstrated poor overall lower limb alignment (with less than 60% of knee separation distance) during landing compared to only 8 after training. Practical Applications: While implementing a program in an attempt to reduce the risk of frequently occurring ACL-injuries in female basketball players, it may be advantageous to combine traditional neuromuscular re-training on landing mechanics with sports-specific performance enhancement training program. This appears to result in more optimal outcome by providing not only a reduction in the risk of serious knee injuries, but also an overall improvement in athletic performance. CONCLUSIONS: This neuromuscular training program is effective in improving both the lower limb alignment during landing activity, thus reducing the risk of knee injuries, and performance parameters of maximal aerobic capacity, vertical jump height, and the 20-yard dash time in high school female basketball players.

The Drop-Jump Video Screening Test: Retention of Improvement in Neuromuscular Control in Female Volleyball Players

A valgus lower limb alignment is commonly documented during noncontact anterior cruciate ligament injuries. We previously developed a videographic drop-jump test to measure overall lower limb alignment in the coronal plane as a screening tool to detect such an abnormal (valgus) position on landing. A neuromuscular retraining program developed for female athletes was shown to be effective in improving lower limb alignment on this test immediately after completion of training. What remained unknown was whether these improvements would be retained for longer periods of time. Therefore, this study was undertaken to determine if these improvements in overall lower limb alignment would be retained up to 1 year after the training. Sixteen competitive, experienced female high-school volleyball players underwent the video drop-jump test and then completed the neuromuscular retraining program. The program consisted of a dynamic warm-up, jump training, speed and agility drills, strength training, and static stretching and was performed 3 times a week for 6 weeks. The athletes repeated the drop-jump test immediately upon completion of training and then 3- and 12-months later. Significant improvements were found in the mean normalized knee separation distance between the pre and posttrained values for all test sessions (p < 0.01). Immediately after training, 11 athletes (69%) displayed significant improvements in the mean normalized knee separation distance that were retained 12 months later. Five athletes failed to improve. The video drop-jump test, although not a risk indicator for a knee ligament injury, provides a cost-effective general assessment of lower limb position and depicts athletes who have poor control on landing and acceleration into a vertical jump.

Assessment of Lower Limb Neuromuscular Control in Prepubescent Athletes

Background Although neuromuscular indices have been extensively studied in adolescents and adults, limited data exist for prepubescent children. Hypothesis No differences exist between prepubescent boys and girls in lower limb strength, symmetry on single-legged hop testing, and limb alignment during drop-jump testing. Study Design Cross-sectional study (prevalence); Level of evidence, 1. Methods The authors tested 27 female and 25 male athletes who were aged 9 to 10 years and matched for both body mass index and years of organized sports participation. In a drop-jump screening test, the distance between the right and left hips, knees, and ankles was measured as an indicator of lower limb axial alignment in the coronal plane. The distance between the knees and ankles was normalized by the hip separation distance. Quadriceps and hamstrings strengths were measured isokinetically at 180 deg/s. Lower limb symmetry was determined from 2 single-legged hop function tests. Results Boys demonstrated greater mean absolute and normalized knee and ankle separation distances on the drop-jump test. Even so, 76% of boys had a normalized knee separation distance of 60% or less of the hip separation distance, as did 93% of girls, indicating a distinctly valgus alignment. There were no differences between the sexes in quadriceps and hamstrings peak torques, hamstrings/quadriceps ratio, time to peak torque, total work, or lower limb symmetry values. Conclusions A high percentage of the prepubescent athletes studied had a distinctly valgus lower limb alignment during the drop-jump test and a lack of lower limb symmetry during the hop tests. These same indices have been hypothesized to increase the risk for knee ligament injuries in older athletes. Neuromuscular training may be needed to address these issues in children.

The Drop-Jump Screening Test

Background A valgus lower limb alignment has been noted during noncontact anterior cruciate ligament injuries. A video dropjump test can indicate an athlete's ability to control lower limb axial alignment in the coronal plane. Hypotheses Female athletes have decreased knee separation distances on landing and acceleration; male athletes have a neutrally aligned lower limb position. A neuromuscular training program will significantly increase knee separation distance in female athletes. Study Design Cohort study; Level of evidence, 2. Methods The authors tested 325 female and 130 male athletes aged 11 to 19 years. The distance between the hips, knees, and ankles was measured during a drop-jump test. The separation distance between the knees and ankles was normalized by the hip separation distance. A neuromuscular training program (Sportsmetrics) was completed by 62 female athletes, and their jump-landing characteristics were reexamined. Results A marked decrease in knee separation distance was found on takeoff in 80% of female athletes and in 72% of male athletes. There was no difference between male and female athletes in the normalized knee and ankle separation distance during the landing and takeoff phases. The knee separation distance on landing was 23 ± 9 cm in the female athletes and 22 ± 8 cm in the male athletes. The normalized knee separation distance was 51% ± 19% in the female athletes and 51% ± 15% in the male athletes. After training, statistically significant increases were found in the female athletes in the knee separation distance on landing (29 ± 8 cm, P<. 0001) and in the normalized knee separation distance (68% ± 18%, P<. 0001). The trained female athletes had significantly greater knee separation distance and normalized knee separation distance than did the males (P<. 0001). Conclusions The majority of untrained female and male athletes demonstrated a valgus alignment appearance on the video test. After neuromuscular training, female athletes had improved knee separation distances and a more neutral lower limb alignment on landing and takeoff.