The standardized jump-landing task consists of 2 segments: (1) subject jumps down from box and lands on ground and (2) subject immediately jumps vertically upward as high as possible. 

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... knee valgus moments during a drop-landing task were at an increased risk of sustaining an ACL injury. 19 Although knee valgus angle and moment are identified as risk factors for ACL injury, this does not imply that isolated knee valgus is the primary ACL injury mechanism because isolated knee valgus does not facilitate sufficient load to injure the ACL without first causing medial collateral ligament injury. 7,15,28-30 Rather, knee valgus occurring in combination with other ACL loading mechanisms, such as anterior tibial shear force, may generate significant ACL loading between knee flexion angles of 0 ° and 40 ° . 28 The presence of faulty movement patterns in addition to knee valgus likely contributes to an elevated risk of noncontact ACL injury. Women have a higher incidence of ACL injury relative to men performing the same activities. 18 Thus, gender differences in sagittal plane and transverse plane motions at the hip and knee are also hypothesized to be potential risk factors for ACL injury. Potential risk factors in these planes include decreased knee flexion angle, 11,27,34 increased anterior tibial shear force, 12 decreased hip flexion angle, 11,25,26,34 increased hip internal rotation angle, 11 and increased knee internal rotation angle 31 during dynamic activities. To identify subjects at high risk for ACL injury it is necessary to have a standardized tool for detecting the presence of multiple high-risk movement patterns. The Landing Error Scoring System (LESS) is an inexpensive clinical assessment tool that we developed to provide a standardized instrument; it uses 2 standard video cameras for identifying potentially high-risk movement patterns (“errors”) during a jump-landing maneuver. Laboratory- based motion analysis systems are undoubtedly the gold standard for investigating biomechanical risk factors. However, because of time and cost constraints they are an impractical means to perform large-scale mass screenings with the goal of identifying subjects with high-risk movement patterns. To be feasible, a clinical assessment tool for high-risk landing mechanics should be brief, easily imple- mented as part of a large-scale team-screening session, and should provide a valid and reliable measure of landing biomechanics. We developed the LESS to meet this need. The purpose of this study was to investigate the con- current validity and reliability of the LESS. Laboratory- based 3-dimensional motion analysis was used as the gold standard against which we assessed the validity of the LESS. We hypothesized that the LESS would be able to distinguish between subjects with different joint kinematics and kinetics in the sagittal, frontal, and transverse planes of motion. In addition, we hypothesized that women (who are at higher risk of ACL injury) would have worse LESS scores compared with men. We collected LESS data on 2691 subjects who were incoming freshmen at the 3 large US military academies to compare 2 motion analysis systems: a sophisticated laboratory system (gold standard) and an inexpensive field analysis system (LESS) using 2 commercial video record- ers. Each subject was analyzed simultaneously with the laboratory and field motion analysis systems. The kinematic and kinetic measures from the 3-dimensional motion analysis were used as the gold standard to assess the validity of the LESS. We also examined whether the LESS varied by gender, and established the intrarater and interrater reliability of the LESS using multiple raters for a subset of 50 subjects. This study uses data from the first 2 years of enrollment in the JUMP-ACL (Joint Undertaking to Monitor and Prevent ACL Injury) study, a prospective study of biomechanical risk factors for ACL injury. There were 2691 participants (men: N = 1655, height = 178.29 ± 7.12 cm, weight = 77.54 ± 12.34 kg; women: N = 1036, height = 165.94 ± 6.63 cm, weight = 63.12 ± 7.88 kg) included in this study. Participants were incoming freshmen at the 3 largest US military academies who were deemed fit to participate in a physically demanding military training program and were preparing to participate in competitive collegiate or recreational varsity sports. Previous knee injury was not an exclusion criterion for participation in this study, but participants had to be healthy and free of orthopaedic injury at the time of testing. All subjects signed an informed con- sent form approved by multiple internal review boards before entering the JUMP-ACL study. Data were collected during July/August 2005 and July/August 2006. The LESS data (inexpensive field analysis using 2 standard video cameras) and 3-dimensional motion analysis (gold standard) were collected simultaneously during a jump-landing task. The jump-landing task incorporated vertical and horizontal movements as participants jumped from a 30-cm high box to a distance of 50% of their height away from the box, down to a force platform, and immediately rebounded for a maximal vertical jump on landing (Figure 1). During task instruction, emphasis was placed on subjects jumping as high as they could once they landed from the box. Subjects were not provided any feedback or coaching on their landing technique unless they were performing the task incorrectly. After task instruction, the subject was given as many practice trials as needed (typically 2) to perform the task successfully. A successful jump was characterized by (1) jumping off of both feet from the box; (2) jumping forward, but not vertically, to reach the force plate below; (3) landing with the entire foot of the dominant lower extremity on the force plate; (4) landing with the entire foot of the nondominant lower extremity off the force plate; and (5) completing the task in a fluid motion. After task instruction and practice jumps (typically 2), electromagnetic tracking sensors were attached and digiti- zation of the local segments and joint centers occurred. Participants performed 3 successful trials of the jump- landing task. Total testing time, including setup, was typically 5 minutes or less per subject. System (LESS). Two standard video cameras (DCR-HC38 MiniDV Handycam Camcorder, Sony Electronics, San Diego, California) captured a frontal plane and sagittal plane view of each subject as he or she performed the testing procedures. Figure 2 shows the specifications of the camera setup. The LESS score is simply a count of landing technique “errors” on a range of readily observable items of human movement. A higher LESS score indicates poor technique in landing from a jump; a lower LESS score indicates bet- ter jump-landing technique. There are 17 scored items in the LESS. Table 1 (see online Appendix 1 for this article at provides opera- tional definitions and scoring details for each item. One set of items addresses lower extremity and trunk positioning at the time of initial contact with the ground (items 1-6). A second set of items assesses errors in positioning of the feet (items 7-11) and are scored at initial ground contact (item 11), at the time the entire foot is in contact with the ground (items 7 and 8), and between the time of initial contact and maximum knee flexion (items 9 and 10). A third set of items assesses lower extremity and trunk movements between initial contact with the ground and the moment of maximum knee flexion angle (items 12-14) or the moment of maximum knee valgus angle (item 15). Finally, 2 “global” items address overall sagittal plane movement and the rater’s general perception of landing quality (items 16 and 17). Operationally, each test jump is videotaped (using 2 “off-the-shelf ” camcorders) from both front and side views. The 2 videos are replayed at a later date and the LESS is scored during replay using pause and rewind controls. To simplify the scoring process, the rater focused on a designated “test leg,” typically defined as the dominant leg. (We use the question, “Which leg do you refer to kick a ball with?” to establish leg dominance.) A trained rater requires 3 to 4 minutes to score 3 jump-landing trials per subject. The LESS scoring sheet is machine-readable and was created using TeleForm software (Cardiff, Vista, California). Training materials and scoring sheets can be downloaded at www.unc.edu/sportmedlab/less. Laboratory-based Motion Analysis. A Flock of Birds (Ascension Technologies, Inc, Burlington, Vermont) electromagnetic motion analysis system controlled by Motion Monitor software (Innovative Sports Training, Inc, Chicago, Illinois) was used to assess lower extremity kinematics at a sampling rate of 144 Hz. A nonconductive force plate (model 4060-NC, Bertec Corporation, Columbus, Ohio) was used to collect ground-reaction forces. Force plate data were collected synchronously with the kinematic data at a sampling rate of 1440 Hz. Previous research has reported that electromagnetic tracking systems provide accurate 2,35 and reliable 2 data for 3-dimensional movement of body segments and joints. Electromagnetic sensors were placed on the subjects’ skin over the L5 spinous process, lateral aspect of the thigh, and anteromedial aspect of the proximal tibia. Data indicating the orientation and position of each sensor relative to a standard range transmitter were conveyed back to a personal computer. Each sensor was placed over an area of the least muscle mass to minimize potential sensor movement and was secured using double-sided tape, pre- wrap, and athletic tape. Six bony landmarks were digitized with the end point of a stylus on which a fourth receiver was mounted. The 6 bony landmarks were the medial and lateral condyles of the femur, medial and lateral malleoli of the ankle, and left and right anterior superior iliac spine of the pelvis. Medial and lateral malleoli and femoral condyles were digitized to determine the ankle joint center and knee joint center, respectively. Left and right anterior superior iliac spine were digitized to determine the hip joint center of rotation using ...