Background Non-contact anterior cruciate ligament (ACL) injuries often occur during rapid decelerations and change-of-direction tasks. Although most high-intensity movements in team sports follow curved trajectories, the biomechanical consequences of curvilinear deceleration remain unclear. This study examined whether curved decelerations increase frontal-plane knee loading associated with ACL injury risk compared with straight-line tasks. Methods Twelve healthy, recreationally active males performed three maximal deceleration tasks in randomized order: (1) straight-line sprint and deceleration (Straight:Straight), (2) curved sprint with straight-line deceleration (Curved:Straight), and (3) curved sprint with curved deceleration (Curved:Curved). Three-dimensional motion capture and embedded force plates were used to compute center of mass (COM) velocity, peak external knee abduction moment (KAM), resultant ground reaction force (GRF), and frontal-plane moment arm. Repeated-measures ANOVAs with Bonferroni-corrected post-hoc tests assessed differences across tasks. Results COM velocity prior to deceleration was similar across tasks (P = 0.36). Peak KAM was significantly greater during Curved:Curved compared with both Curved:Straight (P = 0.007, dz = 1.13) and Straight:Straight (P = 0.036, dz = 0.87). The resultant GRF did not differ significantly between tasks (P = 0.056), whereas the frontal-plane moment arm was significantly longer in Curved:Curved (P = 0.004, dz = 1.04). Conclusion Curved deceleration, independent of approach trajectory, increased knee joint loading through longer frontal-plane moment arms despite comparable entry velocities. These findings identify curvilinear deceleration as an underexplored game situation that may contribute to non-contact ACL injury mechanisms and support the inclusion of curved braking drills in athlete screening and injury mitigation programs.

In the Olympic snowboard halfpipe discipline, rotation is the key indicator of trick difficulty encouraging riders to perform multiple tricks involving a high amount of rotation in their runs. Therefore, this study explored the predictive capacity of angular velocity and airtime on the amount of rotation using deterministic models based on the performance parameters of the Men's Final at the Beijing 2022 Olympic Winter Games. IMU data and video recordings were used to determine the biomechanical performance parameters of 122 tricks performed by 12 riders with random intercept models being employed to develop the aforementioned deterministic models. The ratio between angular velocity and airtime at frontside/switch frontside was greater than 4:1, and at backside/switch backside it was close to 5:1. The coefficient of determination overall indicated a high level of fit, providing significant standardised estimates for all performance parameters investigated. The results showed that, regardless of the direction of rotation, angular velocity was the key performance indicator for increasing the amount of rotation, while airtime showed a comparably small influence. These results are important for coaches and riders in teaching and learning new skills as they indicate to focus more on rotation initiation than increasing jump height.

The assessment of passive metatarsophalangeal joint (MPJ) quasi-stiffness is of growing importance for both athletic performance optimization and clinical monitoring in patient populations. To deepen our understanding and facilitate broader data collection, there is a need to develop a portable device for measuring passive MPJ quasi-stiffness that can be employed in training facilities and clinical settings. Therefore, we designed a portable, pneumatically driven test device to determine the passive quasi-stiffness of the MPJ. The aim of the present study was to investigate the within-day and between-day test-retest reliability of the device. A total of 19 healthy subjects participated in the study. Passive MPJ quasi-stiffness was assessed at three time points: two measurements were conducted on the same day (within-day reliability), and a third measurement was performed on a different day within the same week (between-day reliability). A standardized protocol ensured identical conditions across all three test sessions. The results of the intra-rater intraclass correlation coefficient (ICC (3,1)) comparing passive MPJ quasi-stiffness indicated excellent test-retest reliability for both within-day measurements (ICC = 0.999, 95% CI: 0.99-0.99, p < 0.001) and between-day measurements (ICC = 0.993, 95% CI: 0.98-0.99, p < 0.001). Bland-Altman analysis revealed minimal systematic bias. These findings demonstrate that the standardized protocol and the custom-made device used in this study provide highly reliable results. Its portability, combined with its ease of use and reliability, makes it highly practical for sports and in clinical settings.

INTRODUCTION:Ulcer formation poses a serious clinical problem and has been associated with muscle function and tissue loss in diabetic feet and increased plantar peak pressures during walking. Reduced intrinsic and extrinsic foot muscle strength has been considered to increase the plantar peak pressure at the most affected metatarsal region. We aimed to investigate if a targeted strength training of the toe flexor muscles 1) enhances muscle strength and volume in the diabetic foot, and 2) improves plantar pressure distribution during walking in diabetic patients. RESEARCH DESIGN AND METHODS:Fourteen non-ulcerated diabetic patients performed a monitored toe flexor strength training at 70% of the maximal voluntary isometric contraction on a custom-made dynamometer for eight weeks. The maximal plantarflexion moment at the metatarsophalangeal joints on the dynamometer, the intrinsic foot muscle volume and the plantar pressure distribution during walking were quantified before and after the intervention. RESULTS:Right and left maximal plantarflexion moments increased significantly by 62% (p < 0.001) and 49% (p < 0.001), the intrinsic muscle volume increased by 6.4% (p = 0.018) and the peak pressures decreased at the second (p < 0.001) and lateral (p < 0.01) metatarsal region each by 11% following the training. CONCLUSIONS:Muscle function and tissue loss in diabetic feet can be counteracted by a targeted strength training program. Improved toe flexor muscle strength reduces plantar peak pressure at common ulceration sites.

Ankle injuries are among the most common injuries in sports. Kemler et al. have reported intermediate rates in Dutch children but rising substantially in adolescents (15-24 y). The aim of this study was to investigate the influence of the manually applied external loads on ankle movement during simulated physical examination. Computational simulations of the AnteriorDrawerTest (ADT), TalarTiltTest (TTT) and MedialSutalarGlide (MSG) Test were performed. A computational model was developed in AMS v.6.0.4. (AnyBody Technology A/S, Denmark). The model included 3D representations of tibia, fibula, talus and calcaneus, obtained from CT scans of a specimen. The tibia was fixed in space, with one translational DOF between tibia and fibula in the mediolateral direction. ISB recommendations were followed to construct the tibial and calcaneal reference frames, while the talar reference was aligned with the tibia's. Ankle ligaments were included into the model using anatomical atlases and pictorial essays (Golano et al., 2010). A contact model was defined for the representations of the articular surfaces between adjacent bones. The contact force between the articular surfaces was computed in respect to the penetration volume using the FDK solver within AMS. Anterior force was 80 N anteriorly for ADT simulation, inversion moment was 6 Nm for TTT, and MSG forces were 80 and 150 N at varied contact points. Three ankle integrity scenarios were compared: all ligaments intact (IN), no ATFL and no ATFL + CFL. Foot flexion (DP) was varied from −20–20°. Application point of the ADT and TTT simulations (left) and the selected application points for the MSG simulations (right). Tibia reference frame (blue), talus (green) and calcaneus (red). Displacements for MSG simulations was 0.1-2 mm laterally, coupled to inversion of 0.6-5.8° depending on force application location. For TTT, calcaneal inversion of talus and calcaneus ranged arount 5–10° and increased to over 40° with ruptured ATFL and CFL. Further results to be presented. The proposed model demonstrated biomechanical behavior consistent with clinical observations. These results provide suggestions for the application and interpretation of the physical examinations tests. Such models are useful for interpretation and potential adaptations of such tests for injured ankles of young athletes, whos joint composition is not fully matured.

Since functional clinical gait analysis was first established in the 1990s, numerous studies have proven it's worth in surgical decision making particularly in children with cerebral palsy. From a health care perspective, an increase of surgical volume in paediatric sports medicine has been reported. Limitations are given by the simplicity of the biomechanical models, mainly providing joint kinematics and net joint loading, but no detailed information on, e.g., load distributions within a joint across muscles within a muscle group. Recently researchers and engineers have developed more detailed musculoskeletal (MSK) models allowing to take individual anatomy into account. Individualised MSK models will provide deeper insights into musculoskeletal loading, in particular in children and patient groups with compromised function. Modern imaging technology, machine learning, automated segmentation and their integration into advanced MSK modeling will provide opportunities for biomechanists, engineers and clinicians to colaborate on a new level. Several modeling platforms are in use already with continuous refinements widening the applicability of these models. The prospects lie on an improved understanding of individual anatomy on the load distribution in joint structures. Further, the interaction of the musculoskeletal system with external devices, like orthoses, can be improved. Last, the approach allows for more realistic predictions of surgical outcomes which is desireable in particular in children. In this presentation, the evolvement of MSK modeling will be illustrated with examples from previous publications, on calf muscle function in CP, on the biomechanics of symptomatic snapping hip, the influence of ankle orthotics on ankle joint mechanics, the assessment of knee loading in for injury risk screening in adolescents and a study simulating surgical outcomes based on predicted osteotomy angles. While these examples are taken from studies of different anatomical areas they will serve to derive a conceptual overview and set the scene for this symposium.

A standard clinical CT scan of the hip joint provides only partial femoral morphometrics due to its limited field-of-view and hence is useless for extracting anatomical measures of the entire femur that may become useful in retrospective studies and applied research, such as improving musculoskeletal models. This study used a statistical shape modelling approach to automatically determine seven anatomical measures of the femur from limited field-of-view 3D imaging. A shape model of the full femur was built from a training sample of 50 adult cadaveric CT images and used to predict anatomical measures from full and simulated limited field-of-view segmentations of the training group and a test group (n = 17). The predictive nature of shape modelling allowed for the extraction of additional distal measures not available in limited field-of-view imaging, with no significant difference between full and limited field-of-view input for both femur groups. The predictions of femoral neck-shaft angles were the most accurate (error < 1%), while the other measure predictions had lower errors ranging between 5% and 10%. The presented pipeline offers a technique to automate anatomical landmark extraction from CT imaging and can robustly predict additional anatomical measures not the original scan, increasing the applicability of limited field of view imaging.

Video analyses of ACL injury situations in change-of-direction tasks suggest an elevated injury risk during flatfooted or rearfoot landing. While loading in each individual plane of the knee can contribute to injury, combined loading seems to be the most likely mechanism. This study investigated if knee joint moments are related to the foot strike angle in pre-planned and unplanned handball-specific sidestep cuts performed by n = 51 female handball players. Canonical correlation analysis (CCA) with the foot strike angle at initial ground contact serving as the predictor variable was performed on the knee joint moment vector field (Mxyz). In both conditions, the foot strike angle was related to Mxyz. Subsequently, post-hoc tests were conducted using CCA for moment couples (Mxy, Mxz, Myz) and linear regression for individual moment components. Results revealed that traditional analyses focusing on individual planes only partially explain the observed relationships, particularly during the unplanned cutting condition. Given the time periods in which correlations exist, this study shows that manipulating the foot strike angle has the potential to reduce multi-plane knee loading associated with ACL injury, while limiting analyses to individual planes might underestimate the potential to mitigate ACL injury risk.

OBJECTIVES:Neuromuscular activation and peak external knee abduction moments (pKAM) are risk factors for anterior cruciate ligament injuries during sidestep cutting. This study aimed to: 1) compare thigh muscle activity between preplanned and unplanned sidestep cuts, 2) assess rank correlations of mean thigh muscle pre-activity in both cuts, 3) investigate the relationship between pKAM and thigh muscle activity in 31 experienced female handball players. METHODS:Four-component (vastus medialis, vastus lateralis, semitendinosus, biceps femoris) electromyogram vector fields were compared from 100 ms before ground contact until toe-off using Statistical Parametric Mapping. Spearman's rank correlation coefficient was used to assess rank correlations of mean pre-activity of individual muscles between cuts. Relationships between pKAM and the four-component electromyogram vector fields were assessed using Canonical Correlation Analysis. RESULTS:Four-component muscle activity differed before ground contact and push-off, mostly due to activity differences in muscle pairs. Individual analyses showed lower vastus medialis activity in unplanned cuts right before ground contact. High pre-activity rank correlations were found for vastus medialis and lateralis, moderate for semitendinosus, and none for biceps femoris between preplanned and unplanned cuts. Canonical correlation analyses indicated no relationship between muscle activity and pKAM. CONCLUSION:The knee might be more vulnerable to injury in unplanned tasks due to lower muscular pre-activity. Muscle activity does not vary with pKAM, suggesting passive structures must absorb higher loads with increasing pKAM. Differences in vastus medialis pre-activity and inconsistencies in biceps femoris pre-activity ranking highlight areas for targeted neuromuscular training to better protect the knee against external loads.

Background: Sports with blind or severely visually impaired people requires specific support. For alpine skiing the needed support is commonly given by a human guide. The aim of the current study was to investigate if there are differences between common guiding strategies in regard to the skiers’ body posture and orientation on the skis. Methods: An Intertial Motion Capture System (IMS) MVN Link with 17 motion trackers was utilized to measure the position of the CoM in relation to the feet for 18 participants in total. The conditions ‘Front Guide’ (FG) and ‘Rear Guide’ (RG) were compared. Results: It was found that the visually impaired skiers showed a significantly greater forward lean for FG compared to the condition RG. Conclusions: The FG position appears to be superior a) regarding an appropriate posture on the ski which is assumed to be beneficial for readiness and alertness in most situations of alpine skiing and b) as a safety measure as most knee injuries result from a backward lean position. The results should be considered for the future choice of the guiding strategy and for guidelines in ski schools, clubs and associations.

In snowboard freestyle, rotation is the key indicator of trick difficulty, encouraging riders to perform tricks with more rotation. In many cases, snowboarders learn and practice tricks using training tools such as trampolins and/or landingbags before they transfer this tricks on-snow. It has not yet been scientifically investigated which movement parameters are primarily responsible for the acquisistion of increasingly difficult cork tricks. Hence, the aim of this study was to investigate the influence of each theoretically defined performance parameter on the amount of rotation using deterministic models for halfpipe and kicker tricks, separated for the direction of rotation, performed on a trampoline with a bounce board. Kinematic motion tracking was used to determine biomechanical performance parameters of 157 corks performed by 15 riders, and random intercept models were used to develop deterministic models. The results show that regardless of the discipline and direction of rotation, angular velocity, take-off velocity and the moment of inertia are key performance indicators to increase the amount of rotation. The coefficient of determination showed a high goodness-of-fit and the standardized estimate was highly significant for all investigated performance parameters. These results are important for coaches and riders to teach and learn new skills.

Background Non-contact anterior cruciate ligament injuries during sidestep cutting typically occur rapidly after contact between the foot and the ground with little time for athletes to correct movement patterns. Technique feedback aiming at safe posture at initial ground contact might prove valuable in reducing frontal plane knee joint loading. Objective To assess the immediate effects of individualized technique feedback during sidestep cutting on selected technique variables and peak external knee abduction moments. Design Interventional study. Setting Biomechanical laboratory. Participants 48 adolescent female elite handball players. Interventions Players performed three preplanned handball-specific sidestep cuts on each leg while 3D biomechanics were recorded. Following these cuts, players received tailored technique feedback on their foot strike angle, knee valgus angle, or vertical impact velocity based on cut-off values drawn from an existing data set. If multiple technique variables exceeded their cut-off, variable selection was based on its established relation with performance. Following feedback, three more cuts on each leg were performed. Main Outcome Measurements Peak external knee abduction moment and selected technique variables. Results Feedback aimed at pronounced forefoot landings and reduced knee valgus angles improved technique immediately (+12.7°, p < .001, Figure a and +1.5°, p = .022, Figure b, respectively) and reduced peak external knee abduction moments (-13.4%, p = .003, Figure d and -17.1%, p = .020, Figure e, respectively). Feedback aimed at reduced vertical impact velocities improved technique immediately (-19.0%, p = .010; Figure c); however, peak external knee abduction moments were unaffected (p = .328; Figure f), owing to the variable's unclear relation with technique and therefore lowest priority and smallest sample size. Conclusions Individualized feedback can induce sidestep cutting technique changes immediately, thereby successfully decreasing peak external knee abduction moments and potentially injury risk. Improving technique without sacrificing performance might prove attractive to coaches and players alike.

OBJECTIVE: To compare knee abduction moment (KAM) magnitudes between a generic 180° pivot turn (modified 505 change-of-direction test; m505) and a handball-specific sidestep cut, and to assess ranking consistency. Additionally, to examine the resultant ground reaction force (GRF) and its frontal plane moment arm to the knee to comprehend their contributions to KAM. STUDY DESIGN: Observational laboratory study. METHODS: High-level female handball players (n = 45) performed the m505 and handball-specific sidestep cut. Resultant GRF, its frontal plane moment arm to the knee, and KAM were obtained and subsequently compared between the tasks. Rank correlation coefficients were employed to assess if variables of both tasks are related. RESULTS: Peak KAM was similar for the m505 and the sidestep cut (1.79 (0.95 – 3.53) Nm/kg vs. 1.64 (0.34 – 3.60) Nm/kg; rB = .25; p = .14). The ranking of the players' peak KAM differed substantially ( rS = 0.26, p = .084), suggesting that different tasks could classify the same player with different injury risk. The m505 generated lower resultant GRF (24 ± 4 N/kg, 95% CI [23, 24] vs. 33 ± 9 N/kg, 95% CI [31, 35]; d = 1.30; p < .001) but longer frontal plane moment arms (7.8 ± 1.8 cm, 95% CI [7.3, 8.4] vs. 5.4 ± 1.5 cm, 95% CI: [5.0, 5.8]; d = 1.36; p < .001) than the sidestep cut. CONCLUSION: A difference in individual ACL injury risk assessment depending on movement type was revealed. While KAM magnitudes were similar across direction-change tasks, player rankings differed. The contributions of resultant GRF and frontal plane moment arms to peak KAM varied between tasks, underscoring the importance of task-specific and individualized injury prevention.

Background Sidestep cutting technique is highly individual and has been shown to influence knee joint loading. However, studies assessing whether individualized technique feedback improves technique and ACL injury-relevant knee joint loads instantly in a sport-specific task are lacking. Purpose To determine the instant effects of individualized augmented technique feedback and instructions on technique and the peak external knee abduction moment (pKAM) in a handball-specific sidestep cut. Additionally, to determine the effects of technique modifications on the resultant ground reaction force and its frontal plane moment arm to the knee joint center. Study Design Controlled laboratory cohort study Methods Three-dimensional biomechanics of 48 adolescent female handball players were recorded during a handball-specific sidestep cut. Following baseline cuts to each side, leg-specific visual and verbal technique feedback on foot strike angle, knee valgus motion, or vertical impact velocity using a hierarchically organized structure accounting for the variables’ association with performance was provided. Subsequently, sidestep cuts were performed again while verbal instructions were provided to guide technique modifications. Combined effects of feedback and instructions on technique and pKAM as well as on the resultant ground reaction force and its frontal plane moment arm to the knee joint center were assessed. Results On average, each targeted technique variable improved following feedback and instructions, leading to instant reductions in pKAM of 13.4% to 17.1%. High inter-individual differences in response to feedback-instruction combinations were observed. These differences were evident in both the adherence to instructions and the impact on pKAM and its components. Conclusion Most players were able to instantly adapt their technique and decrease ACL injury-relevant knee joint loads through individualized augmented technique feedback, thereby potentially reducing the risk of injury. More research is needed to assess the retention of these adaptations and move towards on-field technique assessments using low-cost equipment. Level of Evidence: Level 3

(1) Background: Alpine skiing, with its long history, has experienced numerous innovations and developments on all levels ranging from technology to fashion over the past 120 years. However, teaching approaches for beginners remained quite consistent for many decades and are mainly grounded in experience. The One-Ski-Method (OSM) is an alternative approach to the predominant snowplow (SP) method with the strategy to initially experience and acquire the elementary positions and actions on one ski in order to subsequently transfer these to two skis. The aim of the study was to compare the effects of the SP and the OSM by assessing the position of the ski via load distribution sensors. (2) Methods: A total of 33 participants were groupwise randomly assigned to the two methods and tested via load insoles on the first and the fifth day on a moderate slope for six turns. Between the two measurements, the groups were instructed according to the SP or the OSM methods, respectively. The data were analyzed via Matlab and SPSS. (3) Results: The OSM group showed a significantly greater forefoot load than the SP group (p = 0.029). The SP group developed a greater rearfoot loading from pre- to post testing. (4) Conclusions: The findings make it perceivable that OSM learners acquire a beneficial specific position on the ski due to the exercises of the OSM.

Background Anterior cruciate ligament injury (ACL) prevention programs lack game specificity, and the effect on knee loading and movement technique during sport-specific cutting tasks has rarely been investigated. Objective To determine the effect of a handball-specific ACL injury prevention program in reducing knee joint loading and optimizing cutting techniques. Design Pre-posttest control group design. Setting Biomechanical laboratory. Participant 40 young female elite handball players were assigned to an intervention (INT) group (n = 20) and a control (CON) group (n = 20). Interventions Players performed handball-specific fake-cuts while 3D biomechanics were recorded before (T0) and after nine weeks (T1). The INT performed neuromuscular training, including hip and calf muscle strength exercises and handball cutting technique training, focusing on forefoot landing and avoiding knee valgus. Mixed rANOVAs (group x time) were conducted. Main Outcome Measurements The external peak knee abduction moment (KAM). We furthermore assessed knee valgus angle at initial ground contact, foot strike angle, as well as cutting angle and approach speed. Results Both groups reduced KAM from T0 to T1 (Table, Figure). The knee valgus angle was similar between groups and unchanged over time. Both groups adapted a forefoot landing from T0 to T1. Both groups decreased the approach speed but increased their cutting angle from T0 to T1. There were no interaction effects, indicating similar changes over time in both groups. Conclusions The handball-specific prevention program failed to reduce KAM in the INT. A longer intervention period or different intervention content might be required to induce reductions in KAM and further improve the cutting technique.

BACKGROUND:Lateral ankle sprains are one of the most common injuries in indoor and court sports. Self-reports and case studies have indicated that these injuries occur via both contact and noncontact injury mechanisms typically because of excessive inversion in combination with plantarflexion and adduction of the foot. Video-based documentation of the injury mechanism exists, but the number of cases reported in the literature is limited.PURPOSE:To retrieve and systematically analyze a large number of video-recorded lateral ankle injuries from indoor and court sports, as well as describe the injury mechanism, injury motion, and injury pattern across different sports.STUDY DESIGN:Cross-sectional study; Level of evidence, 3.METHODS:A total of 445 unique video-recorded lateral ankle sprain injuries were retrieved from indoor and court sports of broadcasted levels of competition. The videos were independently analyzed by 2 different reviewers. Outcomes included classification of the injury mechanism according to the International Olympic Committee consensus guidelines, primary and secondary motions of ankle joint distortion, and documentation of the fixation point (fulcrum) around which the foot rotates.RESULTS:Overall, 298 (67%) injuries were direct contact, 113 (25%) were noncontact, and 32 (7%) were indirect contact incidents. Direct contact injuries were especially prevalent in basketball (76%), handball (80%), and volleyball (85%), while noncontact injuries dominated in tennis and badminton (96% vs 95% across both). Inversion (65%) and internal rotation (33%) were the primary distortion motions, with the lateral forefoot (53%) and lateral midfoot (40%) serving as the main fulcrums. Landing on another player's foot was the leading cause of injury (n = 246; 55%), primarily characterized by inversion (79%) around a midfoot fulcrum (54%). The noncontact and indirect landings on floor (n = 144; 33%) were primarily characterized by a distortion around a forefoot fulcrum (69%).CONCLUSION:Two of 3 ankle sprains from online video platforms were direct contact injuries, with most involving landing on another player's foot. The distortion motion seems to be related to the injury mechanism and the fixation point between the foot and the floor. The injury mechanisms varied greatly between sports, and future studies should clearly differentiate and investigate the specific injury mechanisms.

In snowboard freestyle disciplines, the amount of rotation is commonly determined as the sum of rotations around all board axes and is the most important indicator of the trick difficulty across all snowboard freestyle disciplines. Based on the type of rotation, tricks can be classified as flatspins, corks and flips. It is not yet known whether the type of rotation of a trick can influence the actual amount of rotation. Therefore, the aim of this study was to determine the amount of deviation, defined as difference between measured and assumed amount of rotation as a function of trick classification, using kinematic motion analysis. The amount of deviation was positive for flatspins (median: 21 degrees; min: -4 degrees; max: 49 degrees) and negative for corks (median: -25 degrees; min: -89 degrees; max: 12 degrees) and flips (median: -28 degrees; min: -94 degrees; max: 13 degrees). Our results demonstrate that there are ways of execution where riders perform corks and flips with a shortcut and flatspins with a detour. This should be taken into account by judges, coaches and riders. Further research is needed to investigate how the shortcut can be influenced.